E P I Z O O T I O L O G Y

 

   PRINCIPLES AND METHODS

 

 

 

 

 

 

 

 

 

 

    Prof.MVDr Václav K o u b a, DrSc.

 

                                    

 

 Prague 2008

 

 

 

 

 

 

 

 

 

 

 

 

 

                        P R E F A C E

 

 

    The objectives of modern action-oriented epizootiology education/training consist in achievement that the learners:

 

    will know the characteristics of health importance of animal populations, etiological agents and environment, sources and ways of transmission of etiological agents, infection and epizootic processes, influencing factors, diseases common to man and animals and consequences of animal population health and diseases;

 

    will be able to trace disease outbreaks, investigate, analyze, monitor and survey animal population health situation, elaborate strategy and identify measures for animal population health protection and recovery, investigate outbreaks and apply effective measures, elaborate and organize animal health programmes and evaluate their results.

 

    Epizootiology principles and methods are applicable on any specific health and disease of any animal population species, herd, flock and group at any place, time and level.The structure of the textbook is based on three main components - principles of animal population health/disease processes, diagnostic/analytic methods and practical preventive and control methods.

 

   The theoretical study must be combined with practical field training under the real or simulated conditions. Practical  activities start and end in the field and the main criterion is final result  at the grass-root level of animal populations.

 

    The textbook represents important component of a set of teaching and self-study materials for undergraduate and postgraduate courses. Examples of successful practical application of the epizootiology principles and methods can be found also in http://vaclavkouba.byl.cz. In order to facilitate the training and problem solutions a special software EPIZOO has been developed for health/disease analyzing, planning and problem solution at animal population level.

 

 

 

               Prof.MVDr Vaclav K o u b a , DrSc. *)

 

-------------------                     

*) Former:

Chief, Animal Health Service, Food and Agriculture Organization of the United Nations (FAO), Rome; Veterinary Public Health Expert, World Health Organization (WHO), Geneva; Informatics Expert, International Office of Epizootics (OIE), Paris; Editor-in-Chief, global FAO/OIE/WHO Animal Health Yearbook; Member of Education Committee, World Veterinary Association (WVA), Madrid; National Chief Epizootiologist and Technical Director of Veterinary Services, Prague; Professor of Epizootiology, University of Veterinary Sciences, Brno; Visiting Professor of Havana, Mexico City, Kosice and Prague University

            

 

                       TABLE OF CONTENTS

                                                                                                    

 

                                                                                                    

1. Epizootiology: definition, objectives, objects

           and methods

 

2. Animal population and its characteristics  of                           epizootiological importance

 

3. Animal population disease resistance

 

4. Animal population health and disease

 

5. Animal population collective health

 

6. Animal population morbidity and mortality

 

7. Animal population epizootiological structure                     

8. Etiological agents of animal population diseases

 

9. Sources of biological etiological agents

 

10. Transmission of biological etiological agents

 

11. Natural environmental factors

 

12. Interaction animal-etiological agent-environment

 

13. Epizootic process

 

14. Animal population disease nidality

 

15. Diseases common to man and animals

 

16. Economic and social factors influencing epizootic          process 

 

17. Consequences of animal population health and     

        diseases

 

18. Investigation of epizootiological situation

 

19. Epizootiological information system

 

20. Analysis of epizootiological situation

 

21. Epizootiological monitoring and surveillance

 

22. Epizootiological theory, experiments and studies

 

23. Epizootiological strategy and measures

 

24. Active creation of animal population health

 

25. General preventive measures in animal population

 

26. Protection of animal population specific health

 

27. Epizootiological protection of country territory              

 

28. Animal population general health recovery

 

29. Animal population specific health recovery

 

30. Measures against diseases common to man and animals                                                    

31. Epizootiological sanitation

 

32. Planning of epizootiological measures

 

33. Organization of epizootiological activities

 

34. Results and efficiency of epizootiological programmes                                                   

 

B i b l i o g r a p h y

 

A n n e x : Selected epizootiological indicators

 

 

 

 

 


 

 

 

 

1.    EPIZOOTIOLOGY: DEFINITION, OBJECTIVES, OBJECTS AND METHODS

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1.1  Epizootiology definition:

 

     Epizootiology is the science which studies origin, frequency, distribution, development and extinction of animal health and disease at populations, herds and flocks levels as well as causes and influencing factors and based on their analyses defines the methods for creation, protection, improvement and recovery of collective health by reducing, eliminating and eradicating common diseases.

 

     Notes: Name is from Greek: epi=upon; zoon=animal. Syn.: veterinary epidemiology, animal epidemiology, animal population medicine, etc.

 

1.2  Epizootiology objectives

 

a)  Only healthy animal populations, herds and flocks create the conditions for effective and wholesome production, for the protection of human population against diseases from animals, for desirable animal exploitation and welfare. The main objective of epizootiology is to provide the methods contributing as much as possible to these conditions.

 

b)  Following groups of objectives can be distinguished:

 

-   to create actively diseases free animal populations, herds, flocks, groups and territories;

-   to protect infectious diseases free populations, herds, flocks, groups and territories against the introduction of these diseases;

-   to protect non-infectious diseases free populations, herds, flock and groups against etiological agents and factors causing these diseases;

-   to protect human population against diseases transmissible from animals;

-   to improve and recover the health of animal populations, herds, flocks and groups;

-   to reduce, eliminate and finally eradicate specific mass diseases of animals following the order of priorities and respecting feasibility aspects.

 

1.3  Epizootiology objects

 

a)  The main objects of epizootiology are    

- animal populations, herds, flocks and groups

- etiological agents and factors of mass diseases

- environmental factors

        and their interactions determining the origin, development and extinction of animal health and diseases.

These three main objects are called "epizootiological triad".

 

b)  Epizootiology studies

 

aa) animal population characteristics of epizootiological importance such as species and categories structure, functions, ethology, development, resistance and susceptibility, collective health, morbidity, mortality etc.;

 

bb) etiological agents and  their complexes from the point of view of their characteristics of epizootiological importance such as specificity, pathogenity, tenacity, sources, ways of transmission, etc.;

 

cc) environmental factors and their complexes influencing animal populations and etiological agents as well as their interactions;

 

dd) interactions between animal population and etiological agents under different external influences being reflected in collective health, morbidity and mortality, epizootic processes and their characteristics including the nidality as well as in the biological, economic, public health and social consequences;

 

c) Epizootiology covers the population health and disease processes related to any species of animals, to any species of etiological agents and to any influencing environmental factors.

 

1.4  Epizootiology methods

 

a)  Diagnostic methods reveal the epizootiological reality detecting healthy and diseased animals, groups, herds, flocks and populations, etiological agents and their sources and influencing environmental factors in space and time.

 

b)  Descriptive methods consist of the collection, compilation and processing results of the diagnostic activities, available data on animals, etiological agents and external factors.

 

c)  Analytical methods are based upon the results of epizootiological investigations and relevant data processing making possible the evaluation of the true epizootiological situation and its development. The analyses are the bases for decision making on epizootiological strategy, programmes and measures.

 

d)  Statistical methods applying essentially the principles of probability calculations are necessary for processing and interpretation of data of epizootiological importance. The backbone of these methods is the complex of epizootiological indicators.

 

e)  Experimental methods are used for the confirmation of the epizootiological hypotheses and for new methods development and testing.

 

f)  Theoretical methods are based mainly upon the generalization of scientific finding and practical experience as well as modelling and simulation of epizootic processes.

 

g)  Action field methods for creation, protection, improvement and recovery of collective health by reducing, eliminating and eradicating common diseases.

    

 

1.5  Epizootiology division

 

a)  General epizootiology concerns the study of the origin, development and extinction of animal population general (crude) health and general (crude) morbidity as well as the common factors and principles related to general epizootiological strategy and measures. It studies general methodologies applicable on any specific animal health and disease(s).

 

b)  Special epizootiology concerns the study of the origin, development and extinction of animal population specific health and specific diseases as well as the factors and principles related to specific epizootiological strategy and measures. It studies specific methodologies applicable on particular health and diseases.

 

c)  Epizootiology can be divided according to other criteria such as:

 

- transmissibility of etiological agents (epizootiology of transmissible diseases, epizootiology of no-transmissible diseases);

- etiological groups and complexes;

- animal species and categories;

- environmental factors;

- characteristics and phases of epizootiological processes;

- space and time;

- diagnostic procedures (e.g.,sero-epizootiology, clinical epizootiology);

- genetic aspects, molecular biology, etc.

 

1.6  Epizootiology relations to other sciences

 

a)  Epizootiology studies the reality, formulates theories and principles related to mass phenomena in animal population health and disease influencing many other scientific branches. On the other hand it is supported by a series of knowledge and methods of other scientific branches creating interdisciplinary approach and facilitating the synthesis of all relevant aspects for epizootiological diagnosis, analysis and actions. The health/disease mass phenomena are based on individual animals' phenomena which represent integral components of the populations and their characteristics.

 

b)  From the methodological point of view, the human epidemiology is the closest scientific branch. Both have many common principles of study and measures. Homo sapiens belongs from biological point of view also to animal kingdom. Study of diseases common to man  and animals and the measures taken against them which should be perfectly coordinated to achieve common objectives.

 

c)  Among the other related scientific branches belong: biology, zoology, morphology, physiology, immunology, haematology, reproduction, genetics, ethology, etiology, microbiology, parasitology, entomology, toxicology, traumatology, pathology, clinical 'propedeutics', preventive medicine, internal medicine, pharmacology, ecology, animal husbandry, nutrition, zoohygiene, food hygiene, food technology, climatology, geography, statistics, economics, sociology, etc.

 

 

 


 

 

 

2. ANIMAL POPULATION AND ITS CHARACTERISTICS OF EPIZOOTIOLOGICAL IMPORTANCE

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2.1  Introduction

 

  Animal population and its characteristics and dynamics create the background upon which health and disease processes develop. Animal population development changes, horizontal and vertical movements influence significantly the location, development and dynamics of population health and disease.

 

2.2  Population numbers, species and categories

 

a) First step in analyzing animal population is to identify their size in a given space and time. Number of animals represents the basic denominator for the majority of health and disease epizootiological indicators.

              

   Note: Animal population at epizootiological risk is often the denominator in measurement of disease frequency relative indicators.

 

b) The total number of animals can be subdivided according to species (or group of species), categories (breed, strain, sex, age, weight, physiological, genetic and nutritional status, yielding, etc.), territorial and time distributions, etc.

 

2.3  Space aspects

 

a) Space aspects create the framework for disease space distribution and propagation and their analysis.

 

b) Location requires to identify the places according to geographical, ecological, organizational and administrative structures using relevant statistical data and territory maps.

 

c) Density (dispersion) represents the number of animals per one surface measure unit (km2, ha, etc.) in a given territory. Concentration represents the number of animals per one space unit of breeding/production establishment (stable, farm, ranch, etc.). For this purpose there is a need for data on the number, size and distribution of herds, flocks, farms, ranches, zones, etc. using clear-cut definitions.

 

       On the other hand the average value of surface or space measure units per one animal (e.g. stocking rate - ha/animal, m2/animal) is also of epizootiological importance. Increasing animal density and concentration create better conditions for transmissible diseases propagation and vice versa.

 

d) Fluctuation of wild animal populations density reflects in fluctuation of many diseases with natural nidality. Some of them need for their propagation a minimal (critical) value of susceptible animals density (e.g. rabies in fox population).

 

2.4 Time aspects

 

a) Time identification is a must to avoid misunderstanding when evaluating any aspects of animal populations. It must be considered that the number and characteristics of animal populations are changing continuously.

 

b) The number of animals must be distinguished according to time factors: existing at a moment, during a period or in average.

 

c) Duration of the existence of animals is used in other group of epizootiological parameters based on "animal-time" units needed for certain types of morbidity rates.

 

2.5  Ethological behaviour

 

   Ethological behaviour of animal population such as intra and inter-species relations, cooperation, commensalism, mutualism, competition, predacity etc. is of particular epizootiological importance in wild animals.

 

2.6  Animal population dynamics

 

a) Animal populations, herds, flocks and groups are characterized also by permanent changes, development and horizontal/vertical movement influencing the dynamics of animal health and disease.

 

b) Animal population development has different forms. Among them belong genetic, age, morphological, physiological, resistance/susceptibility and ethological changes contributing to the infinite variation of animal disease pictures, courses, and impacts. Among the development criteria can be mentioned: age (at weaning, at a given weight, at first parturition, at market maturity, etc.), weight (weight at birth, at weaning, total litters weight at birth, at a given age, market weight, initial and final weight in feedlots, etc.), growth rate (weight gain to weaning, daily or total live weight gain, rate of gain, etc.).

 

c) Changing number of animals in population can be expressed in following indicators: chronological time series, comparative indexes (current and/or chain), average of changing numbers during sub-periods, seasonality, changing number in reproduction and/or production cycle, tendency (linear, cyclic, ascending, descending, continuing), etc.      A measure of population numeric growth (without migration) comprises addition of new born animals to the population and subtraction of deaths (natural and artificial).

 

d) Horizontal movement of population is characterized by the number of moved (transferred) animals, direction (origin and destination places), distance and velocity (duration). A particular role has international export/import having caused the introduction of many so called "exotic diseases" into specific disease free countries. In wild animals an important role has the migration which could be within the local environment or within major territorial framework up to intercontinental one.

 

e) Vertical movement is  characterized by continuing replacement of one generation by a new one. Following criteria are used: viability index (new born/dead ratio), replacement rate (new born/total number), survival rate (numbers at end/beginning), etc. This movement facilitates the transmission of many infectious diseases from elder generation to a new one within reproduction and production cycles. For reproduction  process evaluation following criteria (indicators) are used: fertility (new born/females of reproduction age), natality (new born/total number), weaned rate (weaned/new born), conception rate, gestation length, parturition intervals, service period, etc.

 

2.7  Production systems and other external factors

 

a) Animal population characteristics, development and dynamics are influenced by different external factors such as breeding, production, marketing and slaughter systems as well as by different ecological factors. Each of them creates different conditions for the origin, development and results of animal diseases.

 

b) Among the breeding and production systems are: primitive natural breeding, extensive breeding and production in pastures, intensive breeding and production, production of industrial type as well as mixed systems. Among other factors belong: concentration, specialization, type and grade of exploitation, technology based on grazing or foraging or other feeding system, confined or non-confined systems, type of mating, genetic programme, hygiene, grade of exposition to wild animals, mechanization, management, grade of commercialization, etc.

 

c) Organization and structure of breeding and production have also the influence on animal health/disease.  Organization with open system requiring to introduce animals from other localities facilitates the introduction of diseases. This is not the case in closed system  being self-sufficient and without a need to introduce animals.

 

d) Marketing systems define the modes and ways of selling animals and their products creating the routes for their movement and places of their concentration (market places) which represent also the routes and concentration of many animal diseases.

 

e) Animal populations are integral parts of respective ecosystems. Therefore following factors must always be taken into consideration: atmospheric (climate, air temperature, rainfall, etc.), geospheric (soil, geomorphological relief, etc.), hydrospheric (water distribution, arid zones, humid zones, etc.) and biospheric (flora, fauna). The biocenosis where the relationship among animals is linked by food chains defines the variety of animals and their populations structures in a particular area.

 

    Note: More information in chapters 11 and 16.    

 


 

 

 

3. ANIMAL POPULATION DISEASE RESISTANCE.

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3.1 Introduction

 

a) Animal population disease resistance is represented by the collective body mechanisms which interpose barriers to the progress of invasion or multiplication of infectious agents or to damage by their toxic products in animals at population and herd/flock levels. The collective resistance is based upon  the resistance mechanisms of individual animals creating a defense complex of animal population.

 

b) Animal population disease resistance (lack of susceptibility) contributes often decisively to the restriction up to interruption of etiological agents circulation and thus to the restriction or interruption of the epizootiological chain, i.e. epizootic process.

 

c) Resistant animals possess specific protective antibodies or cellular immunity as a result of previous infection or immunization, or is so conditioned by such previous specific experience as to response adequately with production of antibodies sufficient to prevent clinical disease following exposure to the specific infectious agents.

 

d) Susceptible animals do not possess sufficient resistance against particular etiological agents to prevent contracting a disease if or when exposed to these agents.

 

e) Immunity is relative. An ordinarily effective protection may be overwhelmed by an excessive dose of the infectious agents or via an unusual portal of entry; may also be impaired by immune-suppressive drug therapy or concurrent disease.

 

f) Degree of specific resistance varies according to the type of etiological agents and their immunizing capacity, the dose of infection, the antibody-forming capacity of the animals, etc.

 

3.2 Factors of general resistance

 

a) General (non-specific) resistance is based on a series of morphological and physiological barriers creating defense lines.  Primary defense serves to hinder or prevent the passage of etiological agents into the animal tissue. Secondary or parenteral defenses deal with such agents which have managed to enter the tissue in spite of primary defense of the animal organism.

 

b) Cutaneous system.  Before the tissue of the body can be reached one of the epithelial coverings, skin or mucous membranes must be penetrated. These integuments, the skin particularly, serve as effective physical and chemical barriers. The sweat contains anti-microbial substances reducing up to destroying many pathogenic microorganisms.

 

c) Mucous membranes are protected by the mucus trapping small particles, including microbial pathogens and exposing them to lysozyme and local antibodies such as immunoglobulin in respiratory secretions and faeces. In the digestive tract mucus gathers into masses which are then carried through the canal with its content. In the respiratory tract most of etiological agents are either coughed up or swept up into the pharynx by the action of the ciliated epithelium and swallowed. Protective role have also mucous membranes secretions and excretions of the conjunctiva, urinary tract, vagina, stomach, intestines, etc.

 

d) Among parenteral defense belong substances such as lysozyme,   properdin, interferon and the complex of phagocytosis and reticulo-endothelial system (RES).

 

   More information see in immunology textbooks.

 

3.3 Inherent specific resistance

 

a) Inherent specific resistance (natural innate immunity) is an ability to resist disease independent of antibodies or of specifically developed tissue response; it commonly resides in anatomic or physiologic characteristics of the host and may be genetic or acquired, permanent or temporary. This resistance is more often genetic in origin and is not dependent on previous contact with etiological agents by the individual or its parents.

 

b) Species-related differences vary greatly  in their resistance to etiological  agents  whether  infectious   or  non‑infectious. Monohostal infections are known only in one species (e.g. equine infectious anaemia in horses). Polyhostal infections are known in many species (e.g. salmonellosis, tuberculosis,etc.).

 

c) Breed-related differences in resistance. Some breeds  may adapt better to certain environments while others fail to  thrive under  similar  conditions. (E.g., the breed N'dama is much more resistant against trypanosomiasis than other breeds).

 

d) Age-related differences in response to infectious diseases may be due to maternal antibodies, previous exposure, etc. (E.g. gastrointestinal and respiratory diseases are in calves with much higher frequency than in adult cattle).

 

e) Physiological and production stages. All animals go through several stages  throughout  their  lives  which  may  be  associated  with  increased  risk  of  disease occurrence. (E.g. in general, the higher producing cows are more likely to develop mastitis due to reduced resistance) than the low producing animals.

 

f) Differences of individuals. Many individual animals under the same conditions and exposure to etiological agents do not become diseased at all when other animals of the same species, category and age can under the same conditions and exposure  become diseased. Physiological and anatomic factors resulting  in  conformational  differences may  be  risk  factors for disease. (E.g. dairy  cattle with  large udders are at greater risk of developing chronic mastitis).

 

3.4  Acquired specific resistance

 

a) Acquired specific resistance (immunity) is a result of previous exposure to an antigen - a natural pathogen or foreign substance for the host. Antigen is a substance (protein, polysaccharide, glycolipid, tissue transplant, etc.) that is capable of inducing specific immune response. Induction of antigen may be by the invasion of infectious organisms, immunization, inhalation, ingestion, etc.

 

b) Immunity is the resistance usually associated with possession of antibodies having a specific action on the microorganism concerned with a particular infectious disease or on its toxin.

 

c) Specific immunity is a state of altered responsiveness to a specific substance acquired through immunization or natural infection. For certain diseases this protection lasts for the life of the individual.

 

d) Passive immunity is conferred by antibodies produced by another host and acquired naturally by a new born from its mother - maternal transfer (via the placenta  before birth,  the colostrum just after birth, via the egg yolk in birds and reptiles) or artificially by administration of an antibody-containing preparation (convalescent or hyperimmune serum, or immune globulin). This immunity is of brief duration (days to month).

 

e) Active immunity is the resistance developed in response to stimulus by an antigen (infecting agent or vaccine) and usually characterized by the presence of antibodies produced by the host.  Active immunity is attained either naturally by infection with or without clinical manifestations, or artificially by inoculation of fractions or products of the infectious agent or of the  agent itself in killed, modified or variant form. (See chapter 26). Active immunity depends on cellular immunity which is conferred by T-lymphocyte sensitization, and humoral immunity which is based on B-lymphocyte response. Active immunity following infection or immunization can last for several months,  years  or even lifelong, depending on the agent or immunogen administered.

 

  Individual immunity is relative and not absolute. It depends on the nature of the agents (particularly their virulence and  invasiveness), the dose of the infectious agents, the route  of infection, the environment and physiological condition  of  the host.

 

f) Antibodies are protein molecules formed by exposure to a "foreign" or extraneous substance, e.g. invading microorganism responsible for infection, or active immunization. They may also be present as a result of passive transfer from mother to new born animal, via immune globulin, etc. Antibodies have the capacity to bind specifically to the foreign substance (antigen) that elicited its production, thus supplying a mechanism for protection against infectious diseases.

 

g) Herd immunity differs from individual host immunity in that the former is dependent on the composition of the population, i.e. on the proportion of infected, incubating, diseased, convalescent, vaccinated, recovered and susceptible animals, and on the presence of alternative hosts and carrier animals within the herd.  Since these proportions are dynamic, herd immunity can vary considerably over time, while host immunity usually is present or absent and remains fairly stable over time, particularly in the case of actively acquired immunity.

 

   The value of herd immunity depends also on  the population dynamics, (number of births, deaths, removals and additions) as well as on the degree of contact between individual animals.  Herd immunity level of  70‑80%  may well provide  the degree of  resistance needed to prevent epizootic occurring.

 

h) The graduation from susceptibility to resistance lead to a weak to strong inhibition of multiplication of the infectious agents which have got through. The maximum possible defense capacity is resistance which excludes the animal from epizootiological chain formations. The distribution of susceptible or resistant individuals with their transition forms, consequently, has a decisive influence on the development of epizootiological chains. Many susceptible animals lead to a rapid or even explosive development of these chains through favourable contact possibilities between etiological agents and the individuals. Conversely, an epizootiological chain formation can be weakened or completely extinguished if a larger part of the population is not susceptible, thereby causing the chance of contact between etiological agents and susceptible animals to become very limited.

 

3.5 Animal population resistance structure and indicators

 

a) Population structure according to resistance degree is composed of resistant animals, susceptible animals and animals resistance-indifferent.

 

b) For their measuring following indicators are mainly used: resistant animals rate as the proportion of these animals in total number and susceptible animals rate as the proportion of these animals in total number.  In concrete cases time factor must be respected, i.e. these general rates to be expressed as prevalence or incidence. See chapter 20.

 

c) Other useful indicator is immunized animals rate (vaccination  coverage of population)  which  could  be  combined  with  herds  or  territory vaccination  coverage. The immune‑effectiveness of vaccines used should be always taken into consideration.

 

 

 

 

 

 

 

 

 


 

 

 

4. ANIMAL POPULATION HEALTH AND DISEASE DEFINITIONS

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a) To use principal epizootiological characteristics, such as animal population collective health and morbidity in a uniform and comparable form, there is a need for clear cut definitions of these phenomena. The definitions of the limits between the animals considered as healthy (non-affected) and diseased (non-healthy, affected, sick, ill, etc.) are of particular importance.

 

b) The general definitions of animal population health and disease depend on the concepts of understanding. There are many different criteria based on biological, economical, public health and social aspects. Within the biological criteria are differences among epizootiological, clinical, morphological, microbiological, serological, parasitological, etc. aspects. The animal considered as healthy from one aspect can be considered as non-healthy  from other aspect. The problems are quite complicated if we consider that this criteria can be applied in combined form.

  

c) Unfortunately, until today does not exist any internationally accepted and used general definition of animal health and disease. Therefore, in the literature many different definitions can be found.  (E.g. the health is a state of dynamic balance in which an individual's or group's capacity to cope with all the circumstances of living is at an optimum level).

 

d) In human medicine for disease is understood any deviation or interruption of the normal structure or function of any part of an organ or functional group of organs that is manifested by symptoms and signs and for health the state of optimal physical, mental, and social well-being and not merely the absence of disease (WHO).

 

e) There are different approaches to general definitions of animal population health and disease depending on the position of the evaluating specialists. There are often differences evaluating the same animals and their groups, herds, flocks and populations between the state and private veterinarians, between specialists of importing and exporting countries, etc. The animal considered as healthy by one specialist can be considered as non-healthy by other one.

 

f) From practical point of view the most important aspect is that which respects first the interest and welfare of human society. This anthropocentric approach means to use first the criterion of animal population utility for the man. However, the other criteria such as biological, ecological and economic ones must be taken into consideration as well.

 

g) Therefore, the animal population health is based not only on absence of clinical signs but also on animal utility (performance) at least at the standard or expected desired level corresponding to a given species and category under the given conditions. The relativity of different criteria for the limits between the health and disease under the changing conditions requires to use official or consented definitions.

 

h) From epizootiological point of view as healthy animals are understood those which are not only free of clinical symptoms of specific disease(s) but also free of etiological agents and living in disease free area without exposition to animals with transmissible disease or to their sources during a particular period.

 

i) For transmissible diseases of major importance national and international organizations issue specific definitions mainly for the trade and control programmes purposes. These definitions are linked with standard diagnostic methods procedure and results interpretation.

 

j) Animal health and disease have their structure and grading according to the levels of different qualitative and quantitative criteria. (E.g. animals investigated serologically are subdivided not only according to result positivity and negativity but also according to the level of antibodies titles).

 

k) Animal population epizootiological structure and grading can be expressed in groups of disease free animals not at risk, disease free animals at risk (indirect, direct), suspect animals (epizootiologically indeterminate), affected animals without clinical symptoms (carriers, eliminators of etiological agents), affected animals with abortive clinical symptoms and affected animals with manifest clinical symptoms.

 

l) Taking into consideration the above mentioned criteria, following definitions can be deduced:

 

aa) Animal population  h e a l t h  is a biological system of dynamic and multiform process in which the animals are free of undesirable morphological and physiological deviations as well as of etiological agents threatening health of other animals or man in the way that it makes possible to utilize the animals and their products at least at the "normal" level corresponding to the given species, race and category under the given conditions.

 

bb) Animal population  d i s e a s e  is a biological system of dynamic and multiform process in which the animals are not free of undesirable morphological or physiological deviations or of etiological agents threatening health of other animals or man in the way that it does not make possible to utilize the animals and their products at least at the "normal" level corresponding to the given species, race and category under the given conditions.

 

 

 

Note:

     International definitions of specific animal health (specific disease free status) related to the export/import policy are described in "OIE International Animal Health Code". International definitions of specific animal diseases of major importance for the export/import policy are described in "OIE Recommended Diagnostic Techniques and Requirements for Biological Products". Both publications are subject of current updating.

 

 

 

 

 

 

 

 

 


 

 

 

5. ANIMAL POPULATION COLLECTIVE HEALTH.

    ===================================

 

5.1 Introduction

 

a)  Animal population collective health is a biological and dynamic system and process based on equilibrated interaction of animals and environment without the interferences of etiological agents and factors.

 

    This process is realized within normal physiological limits under favorable or supportable external conditions without participation of agents or factors able to cause a disease.

 

b)  Collective health is of primary importance not only from preventive medicine but also from economic and social point of view. Only healthy animals are capable to fulfil the existence purpose of a particular population, especially in qualitative and quantitative terms of production of food of animal origin.

 

c) Animal population collective health process represents relative contrast to epizootic process. Quantitative characteristics of collective health expressed in "salubrity" indicators (proportions of healthy animals) are opposite to animal population morbidity indicators. Increasing the values of "salubrity" is accompanied by decreasing of morbidity and vice versa.

 

d) Animal population collective health is not a simple sum of individual animals' health but an integral phenomenon behaving as living being with all the attributes of biological complex with internal and external interactions and relations.

 

5.2 Collective health process

 

5.2.1 Types and stages

 

a) Animal population collective health process as equilibrated interaction between animals and external factors consists in the origin, development and extinction of healthy animal groups. This process maintains as unaffected the animals born as healthy or animals recovered from a disease. These animals continue living under favorable environmental conditions or are able to adapt themselves to less favorable  conditions.

 

b) Collective health process from the etiological point of view can be differentiated basically in general (covering all etiological aspects) and specific (related to specific etiological agents).

 

   As examples of  g e n e r a l  collective health can be mentioned specific pathogen free breeding of birds, infectious diseases free herds or flocks. As examples of  s p e c i f i c  collective health can be mentioned brucellosis free herds of sheep, Newcastle disease free flocks of poultry,etc.

 

 

c) Collective health process has its stages similarly as other biological systems. After the initial stage commencing with minimum value of "salubrity", the process continues through increasing stage to culminating stage with maximum value of 'salubrity' which can be followed by decreasing stage up to eventual extinction stage. The variability of this phenomenon is opposite to the stages of epizootic processes.

 

5.2.2  Collective health forms

 

a) Clinical or manifest form corresponds with the "normal" morphological and physiological status.

 

b) Epizootiological form is characterized by absence of etiologic agents in animals, i.e. not presenting any epizootiological risk for other animals and man. For the declaration that the animals are epizootiologically healthy, they have to originate from healthy parents, disease free herds and zones having no contact and exposure to animals with relevant infectious diseases.

 

c) Diagnostic form is based on favorable results of health/disease investigations of animal population (e.g. cattle herds with negative brucellosis serological tests). Often before declaring a herd as disease free a specific test must be repeated in defined intervals combining different investigation methods.

 

d) Production and reproduction forms are based on yield criteria, i.e. as healthy animal population and herds are understood those with  "normal" productivity and reproductivity.

 

e) There are other criteria as mentioned in chapter 4. In concrete cases it is recommended to combine more aspects in evaluation and declaration of collective animal health.

 

5.2.3  Collective health occurrence

 

a) Population range (width, size, extensity) of collective health is projected in the number and proportion of healthy animals in total. For measuring prevalence rates are used.

 

b) Population collective health process intensity is projected in the number and proportions of new healthy animals in total. For measuring incidence rates are used.

 

c) Range and intensity values of population collective health process are projected in sporadic, localized, dispersed and total occurrence grades.

 

5.2.4  Collective health space aspects

 

a) Space territorial delimitation is linked with the localization of healthy population, herds, flocks and groups using topographic criteria, natural (ecological) or artificial (economical, organizational, administrative) ones.

 

b) Territorial range (size) of healthy animal population and herds and flocks is based on surface measure units in absolute and relative terms.

 

c) Territorial intensity is reflected in the density and concentration of healthy animals expressing the average number of healthy animals per surface or volume measure units.

 

d) For geographical distribution of disease free herds, flocks, zones, etc. epizootiological maps are used.

 

e) Healthy animals movements can be at local, zone, province, national or international levels influencing in the values of population "salubrity" in origin and destination places.

 

5.2.5 Collective health time factors

 

a) For time delimitation of collective health process the evaluation criteria such as the moment, period, duration of the process and its stages as well as time of the beginning and the end are used.

 

b) The variability of this process is reflected also in healthy animals frequency and eventual periodicity in form of cycles and seasonality.

 

5.3  "Salubrity" of animal population

 

a) The "salubrity" of animal population means the grade of health in population, i.e. the proportion of healthy animals in total and their relations with animals with other epizootiological characteristics. All indicators of this kind can be divided according to the quality, content and form of animal health (e.g., clinically healthy, epizootiologically healthy, etc.). (The principles of the rates used below see in chapter 20 and the formulae in Annex).

 

b) General indicator of the "salubrity" is the healthy animals rate expressing the relation between the number of healthy and total animals in a given space and time. However, in concrete cases must be expressed as prevalence, incidence or extinction rates.

 

c) Prevalence rates of healthy animals mean the relations between the number of existing healthy and total number of animals. In concrete cases time aspect of denominator must be well defined (point prevalence rate at a given moment, period prevalence rate during a given period or average prevalence rate during a given period).

 

c) Incidence rates of healthy animals mean the relations between the number of new healthy animals in a given period and total number of animals. In concrete cases time aspect of denominator must be well defined (total number of all existing animals in the period, at a moment or in average).

 

d) Extinction rates of healthy animals  are opposite to incidence rates.

 

e) Replacement rates of healthy animals mean the relation of new healthy animals (born, introduced, recovered) to the total number of healthy animals.

        

5.4 Viability of animal population

 

a) Animal population viability or survivorship means the grade of the ability to survive and reproduce. It can be expressed as the proportion of new born and surviving from the total number of animals. Viability combined with mortality offers the opportunity to evaluate population replacement and "vertical movement".

 

b) Animal population viability index means the relation between natality and mortality, i.e. the relation of the number of new born animals in a given period to the number of naturally dead and slaughtered animals in the same period.

 

c) Conception rate means the number of animals that conceive during breeding from the total females of reproductive age inseminated or fertilized (naturally or artificially).

 

d) Animal population natality rate (crude live birth rate) means the relation of the number of live births in a population over a given period to the total number of animals. In concrete cases time aspects of the denominator must be well defined (existing in the period, at initial moment or in average).

 

e) Animal population fertility rate means the relation of the number of live births in a population over a given period to the total number of females of reproductive age. In concrete cases time aspects of the denominator must be well defined (existing in the period or in average).

 

f) Animal population survival rate (survived animals rate) means the proportion of survived animals at the end of a given period from the total of animals existing at the beginning.

 

g) Animal survival-to-weaning rate  (weaned new born animals rate) means the proportion of weaned animals from total new born animals.

 

h) Breeding animals survival rate means the proportion of bred animals at the end of a given period from the total of animals existing at the beginning of the breeding period.

 

i) Fattening animals survival rate means the proportion of fattened animals at the end of fattening period from the total animals existing at the beginning of fattening period.

 

 

Note: Formulae of selected indicators of animal population health see in Annex.

 

 

 

 

 


 

 

 

6. ANIMAL POPULATION MORBIDITY AND MORTALITY

============================================

 

6.1 Animal population morbidity

 

6.1.1 Introduction

 

a) Animal morbidity representing the grade of disease in populations, herds and flocks is the most important  negative epizootiological characteristics. It means the relation of the number of diseased (non-healthy, affected, infected, invaded, sick, ill) to total number of animals.

 

b) Animal population morbidity can be:

 

aa) general (crude) including animals affected by diseases without specifying the etiology, i.e. by all diseases existing in the given population; it does not take any cause or specific factor into account;

 

bb) specific including animals affected by specific etiological agents or by a specific etiological complex;

 

cc) according to non-etiological aspects, i.e. clinical criteria considering symptoms only, age, etc.;

 

dd) combined, e.g. cause and age specific morbidity rate measuring the morbidity in a certain age group due to a certain cause;

  

ee) cumulative, i.e. sum of subperiods' morbidity values.

 

c) In concrete cases also the form of disease must be defined: acute, chronic, manifest, abortive, subclinical, etc.

 

d) Morbidity indicators are used for measuring disease frequency to analyze: space and time distribution, spread, trends, etc. of the disease; implementation and efficiency of programmes and measures to prevent and eradicate disease.

 

e) Morbidity indicators have as nominator the number of diseased animals as a fraction of the number of animals biologically capable of experiencing the event. These animals are considered the population-at-risk. Total population is not always at risk. Therefore, in concrete cases the denominator must be well defined i.e. if representing population at risk or total population or only those free from disease at the beginning of the period. In concrete cases this phenomena must be clearly indicated to avoid confusion.

 

6.1.2 Rates of diseased animals

 

a) The general basis of these indicators is the relation of the number of diseased animals to the total number in the given space (place) and time. Three groups of these indicators can be distinguished: prevalence, incidence and extinction. The basic difference between prevalence and incidence is that the first is based on the number of existing diseased animals and the latter on the number of new diseased animals (this difference is often confused).

 

   More information see in chapter 20 and in Annex.

 

b) Incidence is a dynamic measurement and prevalence is static. If the disease course is short or fatal the incidence is higher than prevalence. If the disease is chronic or not very infectious the prevalence is higher than incidence. Incidence reflects risk or the likelihood of contracting the disease in a given period. Prevalence reflects the risk of having the disease in a specific time.

           

c) Prevalence rates of diseased animals mean the relations of the number of diseased animals (regardless of when that disease began)  e x i s t i n g  at a given moment or during a given period  or in average  from total number of animals existing at the same moment or during the same period or in average in the same space:

 

-  point (moment) prevalence rate of diseased animals;

-  period prevalence rate of diseased animals (e.g. annual              prevalence);

-  average prevalence rate of diseased animals.

 

   Apparent prevalence rate includes only affected animals with clinical symptoms.      

 

d) Incidence rates of diseased animals mean the relations of newly diseased animals - n e w  cases during a period to a total number of animals taking into consideration the time factors:

 

-  incidence rate of diseased animals to existing total;

-  incidence rate of diseased animals to average total;

-  incidence rate of diseased animals to initial total.

              

aa) Sometimes the incidence rate including all manifest and inapparent cases is called case rate.

 

bb) Cumulative incidence rate is the sum of subperiods' incidence values.

 

cc) Attack rate is a specific incidence rate used in outbreak investigations. It is the proportion of the new cases from the population-at-risk in the outbreak at the beginning of the exposure. It is assumed all animals are specifically healthy (i.e. without the given disease) at the beginning of the outbreak. Attack rate is a cumulative incidence rate often used for particular group, observed for limited periods and under special circumstances, as in an epizootic.

 

dd) Secondary attack rate is the number of cases among contacts occurring within the accepted incubation period following exposure to a primary case, in relation to the total of exposed contacts; the denominator may be restricted to susceptible contacts when determinable.

 

c) Extinction rates of diseased animals mean the relations of  e x t i n c t  diseased animals (due to death, slaughter, remove, recovery) during a period to a total number of animals taking into consideration the time factors:

 

-  extinction rate of diseased animals to existing total;

-  extinction rate of diseased animals to average total;

-  extinction rate of diseased animals to initial total.

 

   Cumulative extinction rate is the sum of subperiods' extinction values.

 

6.1.3 Other indicators related to diseased animals

 

a) There is an other group of indicators based on the relation of the number of diseased animals to the number of animals of other epizootiological characteristics such as healthy, investigated, resistant, susceptible, intrafocal, etc. animals.

 

b) Diseased animals replacement rate is the relation of new cases of diseased animals to existing total diseased animals.

 

c) If the number of new cases (events) occurring during a specified period is divided by the sum of the animal-time units at risk for all animals during the period, the result is the animal-time incidence rate (syn.: interval incidence density). This is a measurement combining animals and time, used also in animal-time incidence and mortality rates.

 

6.2 Animal population mortality

 

6.2.1 Introduction

 

a) Animal population mortality means the relation of the number of naturally and artificially dead animals in a given period to total number of animals in a given space and time.

 

b) Animal population mortality in a wide sense includes not only animals naturally dead (due to diseases) but also artificially dead due to a slaughter (killing).

 

c) Therefore, the indicators of animal mortality have to be distinguished in three group - total (crude) mortality including all the forms of death, natural mortality and artificial mortality.

 

d) All the above mentioned forms of mortality can be subdivided in:

 

aa) general mortality (crude death rate) which does not take any cause or specific factor into account;

 

bb) specific mortality (cause specific death rate) due to a specific cause including animals affected by specific etiological agent or by a specific etiological complex only;

 

cc) according to non-etiological aspects, i.e. using clinical criteria considering symptoms only, age specific death rate, etc.;

 

dd) combined mortality, e.g. cause and age specific death rate measuring the mortality in a certain age group due to a certain cause.

 

ee) cumulative mortality is the sum of subperiods' mortality values.

 

6.2.2 Indicators of animal population total mortality

 

a)  Animal population mortality rates are based on the relation of the total number of dead animals to the total number of animals in a given space and time. In concrete cases time factors must be well defined distinguishing following indicators:

 

- animal mortality rate to existing total (during a period)

- animal mortality rate to average total (during a period)

- animal mortality rate to initial total.

 

b)  Proportional mortality rate expresses the proportion of the deaths due to a particular cause from the total number of deaths in a given space and period.

 

6.2.3 Indicators of natural mortality

 

a)  Animal population natural mortality rates are based on the relation of the total number of naturally dead animals (due to diseases, advanced age, hunger, etc.) to the total number of animals in a given space and time. In concrete cases time factors must be well defined distinguishing following indicators:

 

- natural mortality rate to existing total (during a period)

- natural mortality rate to average total (during a period)

- natural mortality rate to initial total.

 

b)  Proportional natural mortality rate expresses the proportion of the number animals  naturally dead due to a particular cause from the total number of naturally dead in a given space and period.

 

c)  Neonatal mortality rate (the age range for neonates must first be decided) expresses the proportion of the number of neonates dying in a given age range from the total new born animals.

 

d)  Abortion rate expresses the relation of the number of abortions to the total number of females of reproductive age in a given space and period.

 

6.2.4 Indicators of lethality (case fatality)

 

    Animal population lethality rates are based on the relation of the total number of naturally dead animals due to specific disease to the total number animals diseased by the same cause in a given space and time. In concrete cases time factors must be well defined distinguishing following indicators:

 

- animal lethality rate to existing total

- animal lethality rate to average total

- animal lethality rate to initial total.

 

6.2.5 Indicators of artificial mortality

 

a)  Animal population artificial mortality rates are based on the relation of the total number of slaughtered animals during a given period to the total number of animals in a given space and time. In concrete cases time factors must be well defined distinguishing following indicators:

 

- slaughtered animals rate to existing total

- slaughtered animals rate to average total

- slaughtered animals rate to initial total.

 

b)  Proportional artificial mortality rate expresses the proportion of the number animals  slaughtered  due to a particular cause from the total number of slaughtered in a given space and period.

 

c)  Condemned animals rate expresses the proportion of the number of slaughtered or sanitary killed animals condemned and destroyed to the total number of animals in a given space and period.

 

           

Note: Formulae of selected indicators of morbidity and mortality see in Annex.

              

 

 


 

 

 

7. ANIMAL POPULATION EPIZOOTIOLOGICAL STRUCTURE

===============================================

 

7.1 Introduction

 

a) Animal population epizootiological structure is the composition of this population according the size and proportions of its parts of different epizootiological characteristics.

 

b) The grades of "salubrity" and morbidity are bases for this structure.

 

c) Each population has its own epizootiological structure according to animal health/disease situation and development related to changes in the characteristics of animals, etiological agents and environment. The structure is a relatively dynamic phenomenon.

 

d) The skeleton of the structure is relative and it must be considered as artificial (based on professional consensus); in reality it goes smoothly from the minimum to maximum values of respective measure units.

 

e) Different grades of population health/disease and their forms require different approach to a given situation and ask for different measures.

 

7.2 Etiological, clinical and morpho-physiological aspects

 

7.2.1 Etiological aspects

 

a) The structure according to specificity of etiological agents:

 

   - general including all the aspects of etiological factors, i.e. applying general (crude)"salubrity" and general (crude) morbidity;

 

   - specific based on specific "salubrity" and specific morbidity.

 

b) The structure according to the quantity of specific etiological agents:

 

- animals without specific etiological agents

- animals with limited quantity of these agents

- animals with high quantity of these agents.

 

   This criterium is applied mainly in parasitic diseases such as helminthiases combining aspects of their relative range (proportion of affected animals) with intensity (number of helminths).

 

7.2.2 Clinical aspects

 

a) Clinical criterion is widely used for dividing animal population in a structure according clinical signs:

 

- animals clinically healthy

- animals clinically indeterminate (including suspect animals)

- animals clinically diseased (with clinical signs).

 

   This is applicable for general aspects as well as for specific disease aspects.

 

b) This structure based on clinical investigation only cannot provide true epizootiological picture because of covering only an apparent part of affected animals and not all.

 

c) Clinical criterion has major importance in diseases with high grade of clinical manifestation.

 

7.2.3 Morphological and physiological aspects

 

a) According to morphological and physiological criteria (reflected to some extent also in clinical manifestation) animal population structure can be composed basically in:

 

- animals without morphological/physiological changes (general or specific)

- animals indeterminate from the morphological and physiological point of view

- animals with morphological/physiological changes (general or specific).

 

b) There are many criteria of this kind, e.g.:

 

- levels of specific antibodies titles

- levels of haematological values

- levels of biochemical values

- levels of histological changes

- levels of specific allergy reactions, etc. 

   

7.3 Epizootiological aspects

 

   According to epizootiological criteria animal population structure is based on the skeleton composed from animals epizootiologically healthy, indeterminate and non-healthy.

It has to be distinguished if the structure is based on general or specific health/disease.

 

7.3.1 Part of epizootiologically healthy animals

 

a) Animals epizootiologically healthy are free of etiological agents and having no any direct or indirect contact with diseased animals or other sources of etiological agents.

 

b) According to the grade of exposure to the sources of etiological agents (diseased animals, foci, etc.) this part is subdivided in:

 

- animals epizootiologically healthy non exposed

- animals epizootiologically healthy exposed (at risk).

 

c)  Animals exposed (at risk) are subdivided in:

 

- animals epizootiologically healthy directly exposed

- animals epizootiologically healthy indirectly exposed.

 

7.3.2 Part of epizootiologically indeterminate animals

 

a)  As animals epizootiologically indeterminate are considered those which have not yet been identified if they are healthy or non-healthy. In this part suspect and dubious animals are also included. Suspect animals are those which health history and symptoms suggest that it may have or be developing some communicable disease.

 

    This part is artificial, transitional and temporal used only up to the final decision.

 

b)  Indeterminate animals are subdivided according to the relation to diseased animals and other disease sources in:

 

- animals-direct contacts

- animals-indirect contacts.

 

c)  Indeterminate animals are subdivided according to clinical manifestation in:

 

- animals with clinical symptoms

- animals without clinical symptoms.

 

7.3.3 Part of epizootiologically non-healthy animals

 

a) Epizootiologically non-healthy animals are those which cannot be included in the two above-mentioned parts, i.e. animals showing clinical signs of disease or so called subclinical cases determined by laboratory tests.

 

b) Non-healthy (diseased, infected, invaded, affected, sick, ill) animals are subdivided according to the presence/absence of etiological agents in:

 

- non-healthy animals being hosts of etiological agents

- non-healthy animals free of etiological agents.

 

c) This part of animals can be subdivided according to elimination of etiological agents in:

 

- non-healthy animals - eliminators of etiological agents

- non-healthy animals - non-eliminators of etiological agents.

 

d) Non-healthy animals are subdivided according to clinical criteria in:

   

- non-healthy animals with clinical symptoms

- non-healthy animals without clinical symptoms (which can be detected only by particular laboratory or allergic investigations).

 

e) Non-healthy animals without clinical symptoms are subdivided in:

 

-  animals affected subclinically with inapparent                                      morphological or physiological changes

-  animals-simple latent carriers of etiological agents.

 

7.4  Structure evaluation

 

a) Animal population epizootiological structure can be evaluated in absolute data or in relative data (proportions).

 

b) Using absolute data the structure is based on simple sizes (number of animals) of partial components of different epizootiological characteristics.

 

c) Using relative data the structure is based on the rates (proportions) of the sub-parts of animals with different epizootiological characteristics (e.g. prevalence rate of healthy animals, prevalence rate of indeterminate animals and prevalence rate of diseased animals).

 

 

 


 

 

 

8. ETIOLOGICAL AGENTS OF ANIMAL POPULATION DISEASES

===================================================

 

 

8.1 Introduction

 

a) Etiological agents (causing agents of disease) are the factors, such as microorganisms, chemical substances, physical phenomena, etc., whose presence, excessive presence, or (in deficiency diseases) relative absence is essential for the occurrence of a disease.

 

b) A disease may have a single agent, several independent alternative agents (at least one must be present), or a complex of two or more factors whose combined presence is essential for the development of the disease.

 

c) Majority of epizootiological techniques which has been originally developed for the study of animal infectious diseases is also suited for non-infectious diseases.

 

d) In this chapter only the characteristics of epizootiological importance are described.

 

8.2 Biological etiological agents

 

8.2.1 General aspects

 

a) Biological etiological agents are an animal or vegetable organisms that live on or in animal macroorganism and derives its nourishment therefrom.

 

   An obligate pathogen-parasite is one that cannot lead an independent non-parasitic existence. A facultative pathogen-parasite is one that is capable of either parasitic or independent existence.

 

b)  Among biological etiological agents (infectious agents) belong pathogenic viruses, bacteria, rickettsia, fungi, protozoa and  helminths that are capable of producing infection or infectious disease. Among biological etiological agents belong also some species of pathogenic arthropods.

 

8.2.2 Specificity

 

a) Specificity of etiological agents is fundamental for  differentiation of specific diseases and epizootiological situation based on morphological, physiological, genetic, biochemical, etc. features of these agents.

 

b) Specificity has different levels of biological classification within the respective hierarchy. The levels begin with biological class, being subdivided according to biological order, family, genus and terminate with biological species eventually subspecies (types, subtypes).

 

c) There are many thousands of etiological agents species already known. The complexity is stressed by permanent changes, the origin of new species and subspecies combined by disappearance of others.

 

d) If we consider this enormous spectrum of etiological agents and their dynamic changing properties, then it can be appreciated the complexity of epizootiological problems and difficulty to decide about the most effective practical preventive and control measures.

 

e) On the other hand the knowledge of specificity facilitates not only etiological diagnosis but also to trace the route of specific agents (types, subtypes). (E.g. "molecular fingerprinting" permits to identify  associations  between  various  subtypes  of  agents  and  certain host species).

 

8.2.3 Pathogenity

 

a) Pathogenity is the capability of infectious agents to cause disease in a susceptible host.

 

b) Pathogenity of agents depends on the  ability to invade the tissues (invasiveness) or to produce toxins (toxigenicity).

 

c) Infectivity is the characteristics of the infectious agents that embodies capability of enter, survive, and multiply in the host.

 

d) The degree of pathogenity is measured by the virulence.  Pathogenic  organisms may be of  high,  moderate or low virulence.  The  virulence of  the same pathogenic organism  may be increased by passage in the susceptible host or  may be decreased by passage in resistant host or  cultivation under unfavorable conditions whereby it may loose its pathogenity completely and becomes avirulent.

 

e)  Changes in pathogenity may be phenotypic or genotypic  in nature.  Phenotypic are transient and confined to the one generation only while genotypic changes result  from a  change in the genome as a result of mutation,  conjugation, or transformation.

 

f)  In general the higher dose of  the agent whether living or non‑living the more likely is the host to be affected as measured by morbidity or mortality. In experiments this  can  be  calculated  as infection dose or  lethal dose to infect 50% (ID 50) or kill 50% (LD 50) of the exposed animals.

 

g) Some of the agents can be conditionally pathogenic (opportunistic agents) acting only under abnormal conditions (e.g. stress of animals).

 

8.2.4 Tropism

 

a) Tropism of etiological agents is specific tendency to penetrate only or mainly into determinate issues or organs of animal macroorganism.

 

b) Pantropism consists in etiological agent ability and tendency to penetrate into the whole body of affected animals while organotropism means the tendency to penetrate into particular organs (e.g. enterotropism, neurotropism, pneumotropism, dermotropism, epitheliotropism, etc.).

 

8.2.5 Selectivity

 

a) Selectivity of etiological agents is natural affinity for particular species of animal hosts (host range), i.e the causing organism may be specific to a certain host(s).

 

b) Some etiological agents may affect only one animal species (monohostal agents) while others may infect a wide range of hosts (polyhostal agents).

 

c) The same agents may be pathogenic to a certain host i.e. susceptible but  be non‑pathogenic to another host which is resistant on the basis of innate or acquired immunity.

 

d) Within a genus there may be variation in host range according to  species. Within a species there may  be various subtypes  such as phage or  plasmid types which show a predilection for certain hosts. In general, the wider the host range, the more likely are the agents to spread and resist to control measures.                        

 

8.2.6 Adaptability

 

a)  Etiological agents adaptability is their ability to adapt themselves to changing conditions of the host and or environment. The adaptation can conduce to increased or decreased pathogenity changing agents impact on epizootic triad among agents-animals-environment.

 

b)  Usually external influences of longer duration may cause the adaptation with the tendency of etiological agents to better survive and/or reproduce. (E.g. resistance of some pathogens against some antibiotics being used for a longer period).

 

8.2.7 Reproducibility

 

a) Reproducibility of etiological agents is their ability to be reproduced keeping the strain alive and ready for further actions in epizootiological chain.

 

b) The speed of reproducibility plays important role in affecting the host and in spreading the particular disease. This influences the amount of infection doses and the intensity of agents elimination.

 

c) Some etiological agents can reproduce only within the macroorganism of the host, some only outside of animal body (e.g. parasites with more complex vital cycle) and some under both conditions.

 

8.2.8 Heritability

 

  Heritability of etiological agents is their ability to transfer specific genes (features) of the species upon new generations keeping the basic innate characteristics.

 

8.2.9 Immunogenicity

 

a) Immunogenicity (antigenicity) is the ability of etiological agents to produce a systemic or a local immunological reaction in the host.

 

b) Antigenic drift - evolutionary changes take place in the molecular structure of DNA/RNA in microorganism during their passage from one host to another. It may be due to recombination, deletion or insertion of genes, to point mutation, or to several of these events. This process leads to alteration (usually slow and progressive) in the antigenic composition, and thus in the immunologic responses of individuals and populations to exposure to the microorganism concerned.

 

c) Antigenic shift - mutation, i.e. sudden change in molecular structure of DNA/RNA in microorganisms, especially viruses, which produces new strains of the microorganism. Hosts previously exposed to other strains have little or no acquired immunity against the new strain.

 

8.2.10 Tenacity

 

a) Tenacity (viability) is the ability of etiological agents to survive outside the host. Some agents can produce spores which are highly resistant to adverse environmental conditions, while other organisms are extremely fragile outside the host.

 

b) Therefore the period of surviving of particular etiological agents in different substances and conditions is extraordinary important for application of sanitation measures and for declaring a surface (area, zones) as free of these agents.

 

8.2.11 Transmissibility

 

a)  Transmissibility is the ability of etiological agents to be transmitted from one host to other.

 

b)  According to transmissibility etiological agents can be divided in:

 

- contagious propagating through direct or indirect contacts    among healthy and diseased animals

- non-contagious propagating indirectly through intermediate animals - carrier of lower biological classification (e.g. arthropods) or through non-alive substances in which etiological agents are able to survive and reproduce (e.g. in soil).

 

8.2.12 Life cycle

 

a) Life cycle of etiological agents is their development process during one generation.

 

b) The majority of microorganism - etiological agents (viruses, bacteria) has their life cycle within the body of a macroorganism - host.

 

c) A part of etiological agents require for the life cycle to pass through more than one host (inter-hosts) composing different life stages (within the body of animals of lower biological classification such as arthropods, etc.).

 

d) Other etiological agents are able to reproduce exclusively or also outside of animal body (e.g. in soil, water,etc.).

 

8.2. Variability

 

    Variability of etiological agents is their ability to change their characteristics under changing conditions. These changes can be temporal or lasting. This is valid for all above mentioned features.

 

8.2.14 Other characteristics

 

a) In many diseases there is a need for interaction of etiological agents. More than one agent is necessary to  produce disease in a susceptible host (e.g. respiratory syndrome disease). Other agents may depress the immune  system  such that a second agent causes serious disease (e.g. virus  diarrhoea infection followed by a severe Salmonella  infection).

 

b) Non‑living agents may also interact with living agent (e.g. intoxication may predispose to infection by certain infectious  agents).

 

8.2.15 Higher parasites

 

   Some higher parasites act only as etiological agents (e.g. warble fly, screwworm) and some also as vectors of different lower etiological agents (e.g. ticks and tick-borne diseases).

 

8.2.16 Conditionally pathogenic and saprophytic microbes

 

a)  Some microbes living under normal conditions inside of animal body are harmless. However, under the worsening conditions of animals (stress, hunger, heat, frost, etc.) they can become pathogens causing diseases. Similar consequences can have complex of microbes living as saprophytes.

 

b) Some agents  may also  cause disease only when the host  resistance is lowered such  as  may occur during drug therapy or intercurrent disease. These agents are called conditional or opportunistic pathogens  and may be  endogenous in origin.

 

b) In this context is not recommendable to mix groups of animals originating from different environmental conditions, i.e. with different internal and external microflora.

 

 

8.3 Genetic etiological factors

 

   Genetic etiological factors cause hereditary diseases (defects) being transmitted from one to other generation. These defects can be lethal, semilethal or non lethal.

 

   These abnormalities can be morphological, functional, trophic, neoplastic, etc.

 

8.4 Chemical etiological agents

 

   Among chemical etiological agents belong poisons from toxic plants, snakes or insect, toxic  chemicals such  as  pesticides, insecticides or  heavy metals.

 

   These agents cause toxicoses, intoxications and toxic residues in products of affected animals.

 

8.5 Physical etiological factors

  

   Among physical etiological agents belong mechanical actions, bites and extreme values of temperature (heat,cold), atmospheric pressure, sunlight, electricity, radiation, etc.

 

8.6 Deficiency diseases etiological factors

 

    Nutritional diseases are caused by the excess or deficiency of macro‑or micro‑elements  in  the diet. Also lack of sufficient amount of drinking water can cause serious disease and death.

 

8.7 Complexes of etiological agents

 

   Relatively often etiological agents act as etiological complexes composed from different agents combining different biological agents with or without chemical and/or physical factors causing diseases with high variability of clinical and epizootiological picture.

 

 


 

 

 

9. SOURCES OF BIOLOGICAL ETIOLOGICAL AGENTS

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9.1 Introduction

 

a)  Sources of biological etiological (infectious) agents are animals, human beings, arthropods, plants, soil or inanimate matter in or on which these agents  survive and from which they can be transmitted to a host.

 

b) Particular types of sources are reservoirs of biological etiological agents in which infectious agents normally live and multiply, and on which they depend primarily for survival and reproduce themselves in such manner that they can be transmitted to a susceptible host.

 

9.2 Characteristics of sources

 

9.2.1 Epizootiological importance of sources

 

a)  The importance of sources depends first on epizootiological importance of respective etiological agents. Other factors are:

 

- time of etiological agents surviving and their ability to reproduce in or on     the source

- external influences on etiological agents in or on the source (changes in        pathogenity, contagiousness,etc.)

- source movement in space and time

- source location in relation to susceptible hosts.

 

b)  Grades of epizootiological importance:

 

aa) primary sources are represented by those in or on which etiological agents can be maintained, survive, reproduce, revitalize and reinforce their pathogenity (virulence) (e.g. diseased animals);

 

bb) secondary sources are  those in or on which etiological agents are only able to survive for some period and serve as their vehicle - intermediary transmission factor (e.g. infected products of animal origin, contaminated objects and substances); some etiological agents are able to reproduce also outside of animal body (e.g. in organic substances).

 

9.2.2 Quantity and extension of sources

 

a)  Quantity of sources can be evaluated in their number, i.e. absolute number of specifically diseased animals, size or weight measure units of contaminated substances and pieces of contaminated objects.   

 

b)  Relative range (width, 'extension') of sources can be evaluated as their affected proportion within the total number of sources units (e.g. percentage of diseased animals from total number, percentage of contaminated part of objects or substances from total number of respective measure units).

 

9.2.3 Quality of sources

 

a) Epizootiological quality of sources of etiological agents depends mainly on their specificity, pathogenity and external influencing factors.

 

b) According to specificity they can subdivided in mono-etiological containing only one species of etiological agents and poly-etiological containing more than one species.

 

c) Epizootiological intensity (capacity) of sources expresses the quantity of etiological agents in infectious doses (per weight, per volume, etc.) or in higher parasites in absolute or average values of their number.

 

d) The environment of etiological agents in or on the source can reanimate or devitalized them.

 

9.2.4 Space aspects

 

a) Localization of etiological agents in or on sources has significant influence on their epizootiological importance. These agents can be distributed in all parts of the source, or in a part only, on the surface or inside the source (with or without access to exterior).

 

b) The distance of sources and susceptible host has decisive role in propagating respective etiological agents. It is logical that direct contact gives better chance for continuing of epizootiological chain than indirect contact or threat to far living animals.

 

c) Fundamental importance has the localization of the sources in relation to epizootiological situation. The source of particular etiological agents in disease free space (herd) is much more important than the same source in space (herd) already affected by the same etiological agents.

 

9.2.5 Time aspects

 

a) All above mentioned characteristics of the sources change during the time.

 

b) Period of surviving of etiological agents defines the duration of a given source. Period of elimination (period of infectiousness) of etiological agents defines the duration of transmission danger from diseased animals.

 

9.3 Type of etiological agents sources

 

9.3.1 Animals as hosts of etiological agents

 

a) Infected animal is an animal who harbours etiological agents and who has either manifest disease or inapparent infection.

 

b) Infectious animal is one from whom the etiological agents can be naturally acquired.  The presence of etiological agents on a body surface (contamination) can be also included in this category.

 

c) Carrier is an infected animal (or man) that harbours a specific etiological agents in the absence of discernible clinical disease and serves as a potential source of infection. The carrier state may occur in an individual with an infection that is inapparent throughout its course (commonly known as healthy or asymptomatic carrier), or during the incubation period, convalescence, and post-convalescence (commonly known as incubatory carrier or convalescence carrier). Under either circumstance the carrier state may be a short or long duration (temporary or transient carrier or chronic carrier).

 

d) Animal-reservoir is defined as the macroorganisms in which etiological agents normally live and multiply (where they maintain and perpetuate themselves) and from which they can be transmitted. The reservoirs can be main (primary), secondary, active, passive, opportunistic, etc.

     

9.3.2 Humans as hosts of etiological agents

 

   Man can have the role of source of etiological agents threatening animal population if he is affected by common disease (zoonosis). There can be different forms such as manifest cases eliminating the etiological agents or asymptomatic carriers.

 

9.3.3 Vectors of etiological agents

           

a) Vectors are invertebrate animals having the role of intermediator facilitating the transmission of etiological agents between host-vertebrate animals. Vectors have extraordinary importance in diseases with natural nidality.

 

b) Vectors' species are reservoirs of etiological agents only when the agent undergoes transovarial or transtadial passages (e.g. overwintering of arboviruses).

 

c) Vectors can be subdivided in biological (active) vectors representing conditions for obligatory or occasional phase of  respective etiological agents life cycle and mechanical (passive) when etiological agents do not entry in biological interaction. The vectors can be also classified as main (primary), secondary, opportunistic, potential, etc.

 

d) Among the vectors belong different species of arthropods, molluscs and helminths.

 

9.3.4 Infected and contaminated products of animal origin

 

   Product of diseased animals can be originally infected or additionally contaminated during their processing, storing or transport. Infected or contaminated meat, milk, eggs etc. play important role as sources of etiological agents having wide territorial distribution.

 

   The body of animals dead due to infectious disease represent also an important source, mainly in case of sporogenic etiological agents.

 

   Also excretions and secretions of diseased animals have the role of sources.

 

9.3.5 Contaminated substances and objects

 

   Contamination is the presence of etiological agents on or in bedding, equipment, instruments, or other inanimate articles or substances including water, feed, soil, air etc.

These substances and objects play the role of passive (mechanical) transmission factors depending on etiological agents species, epizootiological situation, movement and distance of and relation to susceptible hosts.

 

9.3.6 Biological pathogens products

 

   Among the sources belong also the cultures of pathogenic strains and biological products such as  vaccines and serums if containing alive microorganisms able to cause a disease.

 

 


 

 

 

10. TRANSMISSION OF BIOLOGICAL ETIOLOGICAL AGENTS

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10.1 Introduction

 

a) Transmission of biological etiological agents from one host - diseased animal to the other host - susceptible animal represents the basis of epizootiological chain and thus of epizootic process of transmissible diseases.

 

b) The basic factors for disease transmission are etiological agents sources, portals of exit, modes of transfer, portals of entry and susceptible hosts.

 

c) Epizootiological importance of transmission ways depends on their consequences i.e. how far they worsen epizootiological situation and influence epizootic process.

 

10.2 Characteristics of etiological agents transmission

 

10.2.1 Consequences of the transmission

 

   The consequences of etiological agents transmission can be as follows:

 

   - creation of primary outbreaks in distant disease free territories (intercontinental, international, interprovincial etc. transmission)

- creation of secondary outbreaks in affected territory

- creation of secondary outbreaks in perifocal zone

- spread of a disease within the outbreak area

- superinfection of diseased animals

- contamination or super-contamination of products of animal origin, substances and objects

- zero, i.e. without any epizootiologically important consequences representing "blind branch" of epizootiological chain (majority of the cases due to the fact that from enormous quantity of eliminated and transferred etiological agents only very few have the chance to facilitate the continuation of epizootiological chain).

 

10.2.2 Primary and secondary ways of transmission

 

a) Primary ways of transmission are the principal ways and are represented by the transmission by primary sources of etiological agents (e.g. animal-reservoirs movement, direct contact between diseased and healthy animals in contagious diseases, transmission by vectors in vector-borne diseases, etc.).

 

b) Secondary ways of transmission are not principal ways and are represented by the transmission by the secondary sources of etiological agents.(See chapter 9).

 

10.2.3 Relative range of transmission

 

   Relative range (width) of transmission represents the proportion of infected or contaminated part of sources (e.g. diseased animals among the total, contaminated part from total quantity of meat, etc.) being transferred from one place to the other one. This width varies from maximum (e.g. all transferred animals are specific etiological agents reservoirs) to minimum.

 

10.2.4 Intensity of transmission

 

   The intensity of transmission represent the quantity of etiological agents being transferred which can be expressed in infectious doses eventually in helminths and arthropods in absolute or average numbers.

 

10.2.5 Specificity of transmission

 

a) According to epizootiological difference between the origin and destination places the transmission can be:

 

- from affected places, animals or other sources to non-affected places, healthy animals or other potential sources worsening epizootiological situation

 

- between places, animals or other sources with the same epizootiological characteristics without major change in epizootiological situation.

 

b) According to etiological structure the transmission can be:

 

- mono-etiological transferring only one species of etiological agents

 

- poly-etiological transferring more than one species of etiological agents.

 

10.2.6 Space aspects of transmission

 

a) According to the distance the transmission can be divided in: local (e.g. within animal group, herd, flock, village), regional, provincial, national, international (intra-continental, trans- continental).

 

b) According to the size of origin and destination herds/flocks the transmission can be roughly divided in between the herds of the same size, from a grand herd to a small herd and from a small herd to a grand herd.

 

c) According to the branching form the transmission can be without dispersion and conversion (from only one place to other one place), with dispersion (from one place to more places) and with conversion (from more than one place to only one place).

 

d) According to number of host species the transmission can be

to one single host species or to more (multiple) host species.

 

 

10.2.7 Time aspects of transmission

 

a) According to the duration the transmission or length of communicability period can be of a moment (e.g. direct contact - instantaneous transmission), short period (hours, days), long period (weeks, months, years) depending on etiological agents and given conditions for their transfer.

 

   Usually short-time transmission corresponds with high communicability disease and long-time transmission with low communicability disease.

 

b) Speed of the transmission expresses the relation between the distance and time. This factor is of extraordinary importance in so called emergency diseases with rapid spreading (e.g. foot-and-mouth disease).

 

c) According to the frequency the transmission can be continuous (without interruption e.g. contamination of meat by contaminated processing equipment), interrupted or only once.

 

10.2.8 Natural and artificial transmission

 

   Natural transmission is carried out without any human interfering whereas artificial transmission is realized consciously or not consciously by the man.

 

10.2.9 Horizontal and vertical transmission

 

a) Horizontal transmission is the transfer of etiological agents within the same generation of animals. The disease is spread from one individual to another. There are three types of horizontal transmission: contact, vehicle and vector-borne.

b) Vertical transmission is the transfer of etiological agents from one generation to another, e.g. through the placenta  (transplacental transmission), milk (transmammary transmission) or eggs (transovarial transmission). Vertical transmission not only occurs with infectious diseases, but with non-infectious as well (e.g. genetic).

 

c) Vertical-horizontal transmission combines both forms of transfer of etiological agents.

 

10.2.10 Active and passive transmission

 

a) Active transmission is the transfer of etiological agents by their hosts being in interaction with them.

 

b) Passive transmission is the transfer of etiological agents by the animals or man as mechanical carriers, by the contaminated products, substances and objects.

 

10.2.11 Direct transmission

 

   Direct transmission is essentially immediate transfer of infectious agents to a receptive portal of entry through which infection of animals may take place. This may be direct physical contact by touching or sexual intercourse, or by the direct projection of droplet spray (droplet spread) onto the conjunctiva or onto the mucous membranes of the nose or mouth during sneezing, coughing or by biting, etc.

 

10.2.12 Indirect transmission

 

a) Indirect transmission is carried out through secondary (passive) intermediatory vehicles such as inter-hosts, biological vectors, infected or contaminated products of animal origin, substances and objects.

 

b) Indirect transmission can be of two (biphasic) or more stages (polyphasic).

 

c) Indirect transmission can be mechanical (etiological agents survive only without reproduction), propagative (etiological agents survive with reproduction), cyclic (etiological agents pass one stage of development in or on the transmission vehicle) and cyclopropagative combining the two previous ones.

 

10.3 Transmission by animals

 

10.3.1 Prenatal transmission

 

   Prenatal transmission can be carried out through placenta (intraplacentary) or fertile eggs (transovarial).

 

10.3.2 Direct postnatal transmission

 

a) Ingestion of animals-carriers of etiological agents transmissible by susceptible carnivore.

 

b) Simple contact mainly in skin infections and ectoparasitoses.

 

c) Other forms of direct transmission are through biting, sucking, coitus, scraping and licking between healthy and diseased animals.

 

10.3.3 Transmission by animal movement

 

a) The movement (natural, forced) and transport of animals-carriers of etiological agents represents the most important way of disease transmission. Its importance increases by the distance between the origin and destination places. 

 

b) When importing animals in spite of veterinary certificates the risk of transmission exists due to the fact that also clinically healthy animals can be dangerous carriers of etiological agents (not all affected animals is possible to detect clinically or using indirect diagnostic methods).

 

c) Among wild animals the migration is a problem which is difficult to control. It is obvious that among these animals are also diseased ones moving freely from one to another place (migrating birds are able to fly very grand distances).

 

 

 10.3.4 Passive transmission by animals

 

   Passive transmission by animals is the transfer of etiological agents on the surface of non susceptible animals

or through gastroenteric tract without any interaction between them. This form is important in outbreaks of a very contagious disease (e.g. foot-and-mouth disease).

 

10.3.5 Transmission through animals - intermediate hosts

 

   Transmission through intermediate hosts is based on etiological agents transfer between the definitive hosts passing through the body of other animal species in which these agents have one part of their evolution cycle. These interhosts can be vertebrates or invertebrates.

 

10.3.6 Elimination of etiological agents

 

a) Etiological agents escape from animals-reservoirs through portals of exit. Ease of escape determines the importance of a reservoir.

 

b) Portals of exit can be respiratory, alimentary, urogenital, percutaneous, mammary or multiple (in diseases with more than one portal of exit).

 

c) Among the primary vehicle such as excretions, secretions and other body fluids or tissues of diseased animals are faeces, urine, ocular, nasal, vaginal and preputial discharges, saliva, sputum, exhaled air, vomits, blood, skin scabs or ulcers and foetal fluids.

 

  Fecal-oral transmission is based on ingestion of fresh faeces through fecal splash-droplets or coprophagous activity.

 

10.4 Transmission by humans

 

a)  The man can have a role in transmitting etiological agents of zoonotic diseases to animals. Active role have the clinically diseased persons or persons-carriers of zoonotic agents eliminating them in an environment with susceptible animals. The man in many zoonotic disease with natural nidality has the role of final host, i.e. final link of epizootiological/epidemiological chain branch. Enormous increase of human migration and tourism stresses the importance of animal disease propagation by man.

 

b) Passive role have the healthy persons carrying on their body or on their clothes, footwear, etc. etiological agents of animal diseases (e.g. virus of foot-and-mouth disease).

 

10.5 Transmission by vectors

 

a) A vector is a living invertebrate carrier of a disease causing agents. Vector-borne transmission can be mechanical or biological.

 

b) Mechanical transmission includes simple mechanical carriage by a crawling or flying insect through soiling of its feet or proboscis, or by passage of organisms through its gastrointestinal tract. This does not require multiplication or development of the organism.

 

  With mechanical transmission, the agent does not undergo any change while associated with the vector. The transmission interval is usually short and depends on the survival time

of the agents on the body or mouthparts of the vector.

 

c) Biological transmission based on propagation (multiplication), cycle development or a combination of these (cyclopropagation) is required before the arthropod can transmit the infective form of the agents to susceptible animals. An extrinsic incubation period is required following infection before the vector becomes infective. Transmission may be by saliva during biting, or by regurgitation or deposition on the skin of faeces or other material capable of penetrating subsequently through the bite wound or through an area of trauma from scratching or rubbing.

 

d) In biological vectors the agent undergoes some changes. These may be: multiplication, maturation of a phase in the life cycle, sexual reproduction, maturation and multiplication. Biological vectors cannot transmit the agents immediately after becoming infected.  A prepatent period is required while development occurs in the vector or multiplication occurs to provide enough of the agents to infect a new host.

 

e) Some agents are very well adapted to their vectors.  In transovarial transmission the agents are transmitted from the female vector to the eggs (occurs especially in arthropods). In transstadial transmission the agents survive through various stages of nymph development (e.g. occurs          with many arthropod-borne diseases).

 

f) Flying vectors (e.g. mosquitoes) can actively seek out their vertebrate hosts; the flight range of the vector and its biting patterns may determine the extent and rapidity of spread of an infection.

 

g) Non-flying vectors (e.g. ticks, lice, mites and snails) are dependent on passive contact with host; to overcome this disadvantage many  have developed transovarial and transstadial transmission. Water-inhabiting vectors may release infectious organisms into the fluid medium enabling them to be passively disseminated.

 

h) Vectorial capacity means the grade of vector's efficiency in etiological agents transmission.

 

10.6 Transmission by products of animal origin

 

a) Infected, invaded and contaminated products of animal origin such as milk, meat, eggs, semen, hides, etc. can serve as the vehicles of etiological agents facilitating their transmission to new susceptible host animals.

 

b) The circulation of these products almost continuously from the origin place through the processing and storage places to distribution network and enormous numbers of households and other consumption establishments represent a very important epizootiological and epidemiological risk.

 

c) National and international trade with these commodities, if in crude form, facilitates the propagation of many food-borne diseases in man and feed-borne diseases in animals.

 

d) Feeding the animals with the products of diseased or epizootiologically uncertain animals and mainly with their wastes in crude form  represent important way of transmission of many infectious and parasitic diseases.

 

10.7  Transmission by contaminated substances and objects

 

a) Vehicle-borne transmission occurs by inanimate objects that become contaminated such as equipment, instruments, transport means, water, feed or any substances serving as an intermediate means by which etiological agents are transported and introduced into a susceptible host through a suitable portal of entry. The agents may or may not have multiplied or developed in or on the vehicle before being introduced into animal.

 

b) Air-borne transmission is the dissemination of  microbial aerosol containing etiological agents to a suitable portal of entry, usually the respiratory tract. Microbial aerosols are suspensions in the air of articles consisting partially or wholly of microorganisms. Particles in the 1 to 5 micron range are easily drawn into the alveoli of the lungs and may be retained there; many are exhaled from the alveoli without deposition. They may remain suspended in the air for long periods, some retaining and others losing infectivity or virulence.

 

c) Among airborne transmission factors are droplet nuclei (usually the small residues which result from evaporation of fluid from droplets emitted by infected hosts) and dust (small particles of widely varying size which may arise from soil, bedding, contaminated floors, etc.).

 

d) Soil and dust of horizontal surfaces (floors) when indoors can contain etiological agents which can use the soil for reservoir (e.g. mycotic agents); most bacterial pathogens which are soil-borne are spore formers.

 

10.8 Transmission by biological products

 

  The alive vaccines with virulent etiological agents (insufficiently mitigated) and serum containing etiological agents (due to insufficient sterility control) as well as virulent strains cultures with these agents can facilitate their transmission to susceptible hosts.

 


 

 

11. NATURAL ENVIRONMENTAL FACTORS

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11.1 Introduction

 

a) Environmental factors as one of disease determinants act on life, development, characteristics of animals and etiological agents as well as on the interactions between them. All together participate in an integral complex - ecosystem.

 

b) Environmental factors influence significantly animal population health/disease and epizootiological situation. Disease  occurrence is related to the environment of  the  species concerned.

 

c) Natural environmental factors are inorganic (physical and chemical) and organic (biological). They can be divided in atmospheric, geospheric, hydrospheric, biospheric and nutritional.

 

d) The relationship of living organisms and their environment is studied by ecology.

 

11.2 Environment influences

 

   Environment acts on almost all factors which characterize epizootiological situation and define its development. The influence can be positive or negative.

 

11.2.1 Influences on animal population

 

a) Environment represents the conditions of life of all animals. From epizootiological point of view the most important are those that influence animal health and resistance.

 

b) Environmental factors which are within physiological (normal) limits for the animals support population health and resistance against etiological agents and thus block the origin and/or development of diseases. Environmental factors values outside of these limits have opposite impact. Some of these factors can act as disease agents in their own right.

 

c) Infinite variability of environmental factors is reflected in infinite variability of animal health/disease and epizootiological situation.

 

d) The impact of abnormal interaction between the damaging environment and animals can provoke different reactions such as stress (alarm) reaction or adaption to new conditions. Sudden major changes of these factors have negative effect.

 

e) Movement of an animal species into a new environment may result in disease if there is a pathogen present which has a  well‑balanced relationship with  species already present in  that particular environment (e.g. cattle from Europe suffers in tropical Africa by trypanosomiasis more than Bos indicus species).

 

11.2.2 Influences on etiological agents

 

   Environment represents the conditions of life of all etiological agents being outside of animal or vector body. Extreme conditions reduce their ability to survive, reproduce, adapt and act as pathogens. Favourable conditions have opposite effect.

 

11.2.3 Influences on vectors of etiological agents

 

   Environment represents the conditions of life of all vectors of etiological agents. Extreme conditions reduce their ability to survive, reproduce, spread, adapt and act as pathogens vectors. Favourable conditions have opposite effect.

 

11.2.4 Influences on epizootiological situation

 

a) Environmental factors favourable for animals and unfavorable for etiological agents and their vectors create conditions for maintenance of good and improvement of bad epizootiological situation.

 

b) Environmental factors unfavourable for animals and favourable for etiological agents and their vectors create conditions for worsening of epizootiological situation.

 

c) Multifactorial environmental influences multiply the variability of epizootic processes. These influences on one hand support and on the other hand can slow, break or to make impossible the origin and course of epizootic processes.

 

d) Environmental factors influence on the existence and characteristics of etiological agents sources and way of transmission, on the occurrence, frequency, course and spread of animal diseases, their distribution in space and time (e.g. periodicity, seasonality) as well on their consequences.

 

11.3 Characteristics of environment actions

 

a) Environmental factors can act separately or in complex. Generally they act in integral complexes where some have primary and some secondary role.

 

b) Impact on animal health/disease and epizootiological situation depends on the intensity, stability/variability and space and time of environmental factors action.

 

11.4 Atmospheric factors

 

a)  Atmospheric factors comprise the components of weather to which animals are exposed such as rainfall, temperature, solar radiation, humidity and wind (direction and speed).  Abnormal (extreme) values of these factors may affect the health of the host rendering it more susceptible to disease. They can  also affect the survival of etiological agents as well as of the vectors.

 

b)  Air content such as oxygen, chemical and physical pollution substances, dust and air microflora in extreme (abnormal) values have negative influence on animal health resistance and in some cases can provoke themselves (as etiological agents) a disease.

 

b)  Air temperature. Each animal species and vectors can live only in particular zone of temperature depending also on body thermoregulation (e.g. homeothermic animals such as mammals and birds, poikilothermic animals such as fish, reptiles, etc.). Animal species distribution according to thermic geographical zones is reflected also in geographical occurrence of specific animal species diseases (e.g. tropical diseases). 

 

c)  Air humidity. Excessive humidity and in particular if combined with extreme temperature (heat, frost) has not only negative effect on animal resistance but also can cause itself a disease up to fatal cases. This factor influences also geographical distribution of animals, vectors and many etiological agents species.

 

d)  Air movement in form of wind (or draught in stables) as factor influencing animal health depends on its speed and direction. It facilitates spread of etiological agents of respiratory diseases and can transport flying vectors to distant places propagating different animal diseases.

 

e)  Atmospheric pressure decreasing due to reduced oxygen content (e.g. low pressure in high mountains) has influence on "vertical distribution" of animals, vectors and etiological agents species and on their occurrence density. Sudden decrease of air pressure can provoke a fall in resistance and give the change to "sleeping" etiological agents in animal body.

 

f) Precipitations, solar radiation and light in extreme values have similar effect on animals and vectors as other atmospheric factors.

 

g) Climate represents the complex of atmospheric factors acting on land fauna and flora. It can be differentiated in:

 

-  macroclimate or weather of grand territories,              

-  mesoclimate of minor territories

-  microclimate of local size (refers to restricted area where the host, agents, vectors or intermediate host actually live - stable, biotope, etc.)

 

   Climate of inferior stratum where the majority of terrestrial animals live is of particular importance.

 

   Climate influences in a decisive way the life of all terrestrial animals, their species structure, distribution and development under natural conditions what is reflected in animal population health and epizootiological situation. Besides ubiquitous diseases distributed in all the world (e.g. salmonelloses), the other ones can be distinguished as tropical, subtropical, polar, of mild zone, desert, etc.

 

   Microclimate is of particular importance in intensive animal production premises with high animal concentration. Any major deviation can cause important production losses.

 

11.5 Geospheric factors

 

a) Geomorphological relief has the influence on the animal distribution and grade of their territorial isolation due to natural barriers such as mountains (deep valleys, large rivers, etc.). On the other hand the plains (lowlands) facilitate spread of diseases.

 

b) Soils by interacting with climate determine vegetation and the environment in which animals live. The main effect of vegetation is on nutrition. Soils therefore act indirectly as determinant of disease by causing starvation if there is a little or no vegetation or nutritional imbalance. Soils have also effect on the ability of many etiological agents to survive in the environment.

 

   Soils constitute main substrate and natural shelter for terrestrial animals, vectors and microflora including some etiological agents able to survive in these conditions (B. tetani, B. anthracis). Soil types are based on chemical composition, content of organic substances, physical structure, temperature, humidity and soils fauna (including microflora).

 

11.6 Hydrospheric factors

 

a) Hydrospheric abiotic factors representing aquatic environment surrounding animals such as fish, aquatic mammals, a lot of species of inferior classes including some vectors and etiological agents species. Water represents also the temporal habitat for aquatic birds and amphibian animals.

 

b) The influence of these environmental factors on animals and etiological agents depends on water content (salt, pollution), microflora, temperature, movement, hydrostatic pressure, etc.

 

c) Water distribution, reservoirs and currents determine not only aquatic animals distribution but also create natural barriers for terrestrial animals as well as conditions for different vectors and etiological agents requiring for their living  this environment (e.g. mosquitoes, Leptospira spp.).

 

11.7 Biospheric factors

 

     Biospheric factors (biologic climate) are represented by flora and fauna influencing the forms of interactions of animal populations and etiological agents species. All these belong to biospheric factors as their integral component. These factors have a key role in the origin, development and result of animal disease and in particular epizootiological situation.

 

11.7.1 Biosphere

 

    Biosphere, also called as "zone of live" represents the space where animals and plants live. Global biosphere is composed by marine and terrestrial biomasses.

 

11.7.2 Ecosystem

 

a)  Ecosystem is a complex composed of biotic communities and their abiotic environment. The plant and animal life of a region are considered in relation to the environmental factors that influence it; it is the fundamental unit in ecology, comprising the living organisms and the non-living elements that interact in a defined region (e.g. pasture, lake, desert, forest, river, marsh, etc.).

 

b)  Ecosystem function is based on food chain among different components. Plants represent the first , herbivores the second and carnivora the third trophic level. These relations can be expressed in so called "production pyramid", "biomass pyramid" and "number pyramid".

 

c)  Ecoton is the zone where two or more different ecosystems are mixed creating particular conditions for more species of animals, vectors and etiological agents than in individual ecosystems alone (border principle). Therefore the epizootiological situation is there more complex.

 

d)  Ecosystems can be differentiated according to their size, from microecosystem up to macroecosystem:

 

- habitat is a complex of environmental conditions locally delimited occupied by an organism or specific community or population (e.g.,shelter, nest, stable, etc.);

 

- biotope is a biogeographic area with more or less uniform life conditions and populated by a characteristic type of biocenosis (e.g., lake, forest, pastures, etc.);

 

- biom is a grand biogeographic area with a complex of communities characterized by particular climate (e.g. desert, taiga, tropical forest, etc.);

 

- biogeographical region represents a continent or subcontinent with relatively uniform geography, flora and fauna (Australian, Antarctic, Neartic, Agrotropical, etc.); these regions can be subdivided in biogeographical subregions, provinces and districts.

 

11.7.3 Biocoenosis

 

a) Biocenosis or biotic community is the alive (biotic) part of the ecosystem, i.e. plant and animal populations. Every biocenosis has different composition and structure according to animal and plant species. Many animal diseases are result of a complex interplay between animal and plant species.

 

   Structure of animal species has a grand importance for epizootiological situation in a given ecosystem (e.g. wild fauna structure has decisive role in multihostal diseases with natural nidality).

 

b) Each biocenosis can be subdivided not only horizontally in subcommunities but also vertically according to different strata (e.g. subterranean, soil, grass, bush and tree levels).

 

11.7.4 Biotic interactions

 

a) In natural biological communities no one species lives in an isolated form. Their interactions can be:

 

-  competitive, or beneficial or neutral

-  temporal or continuous

-  of vital importance or of minor importance

-  intraspecies or interspecies.

 

b) Intraspecies interactions competing for food tend to avoid overcrowding of the area with limited food resources. Cooperative interactions contribute to form families, herds and communities, to reproduction, protect new born animals, etc. These relations facilitate the spread of transmissible diseases within a given animal species.

 

c) Interspecies interactions can be based on symbiosis (mutualism, comensalism) or antagonism (depredation, competition, obligatory or facultative parasitism, antibiosis, etc.). These relations facilitate the spread of transmissible diseases among different animal species.

 

11.7.5 Nutritional factors

 

a) Nutritional factors are of decisive ecological importance for any animal population, vectors and etiological agents. The life depends on nutritive substances and water cycles as well as on energy.

 

b) Availability of physiological quality and quantity of protein, carbohydrates, fats, salts, mineral elements and vitamins is of vital importance not only for animal surviving but also for their resistance to diseases.

 

c) Distribution and concentration of animal populations are in close relation to availability necessary nutritional factors having decisive impact on spatial distribution of diseases.

 

d) Drinking water is a basic need of any animal influencing not only their physiological functions but also their resistance against diseases.

 

 


 

 

 

12. INTERACTION ANIMAL-ETIOLOGICAL AGENT-ENVIRONMENT

====================================================

 

12.1 Introduction

 

a)  Interaction animal - etiological agent - environment ( e t i o l o g i c a l  t r i a d ) creates the basis of animal disease process.  This multifactorial process can be infectious when caused by biological agents or non-infectious when caused by abiotic agents. Defense reaction of animal is aimed to maintain or reach again physiological balance, i.e. health.

 

b)  Infected animal (as mentioned in chapter 9) is an animal who harbours infectious etiological agents and who has either manifest disease (sick animal) or unapparent infection. Infectious animal is one from whom the infectious etiological agents can be naturally acquired.

 

c) Infection is the entry and development or multiplication of infectious etiological agents in the body of animals or man.   Infestation is the lodgement, development and reproduction of arthropods on the surface of the body .

 

d) Infectious disease is a disease caused by  pathogenic microorganisms (viruses, bacteria, fungi, parasites, etc.) and may be transferred from one host to another or may arise from the host's own indigenous microflora. An infectious disease is not necessarily a contagious disease.

 

e) Contagious disease is a disease capable of being transmitted from one individual to another. Also called a communicable disease.

 

f) Infectiousness is a characteristics of the disease that concerns the relative ease with which it is transmitted to other hosts.

 

g) Non-infectious disease is a disease caused by other than  infectious agent.

 

h) Dose‑response characterizes the relationship between the  agent dose and the host  reaction. 

 

12.2 Postulates of infection process

 

   Following postulates (Evan's based on Henle-Koch model) should be met before a causative relationship can be accepted between a particular bacterial parasite or disease agent and the disease in question:

 

a) Prevalence of the disease should be significantly higher in those exposed to the hypothesized cause than in controls not so exposed.

 

b) Exposure to the hypothesized cause should be more frequent among those with the disease than in controls without the disease - when all other risk factors are held constant.

 

c) Incidence of the disease should be significantly higher in those exposed to the hypothesized cause than in those not so exposed, as shown by prospective studies.

 

d) The disease should follow exposure to the hypothesized causative agent with a distribution in incubation periods on a bell shaped curve.

 

e) A spectrum of host responses should follow exposure to the hypothesized agent along a logical biological gradient from mild to severe.

 

f) A measurable host response following exposure to the hypothesized cause should have a high probability of appearing in those lacking this before exposure (e.g. antibody), or should increase in magnitude if present before exposure. This response pattern should occur infrequently in animals or persons not so exposed.

 

g) Experimental reproduction of the disease should occur more frequently in animals or man appropriately exposed to the hypothesized cause than in those not so exposed.

 

h) Elimination or modification of the hypothesized cause should decrease the incidence of the disease (i.e. attenuation of virus).

 

i) Prevention or modification of the host's response on exposure to the hypothesized cause should decrease or eliminate the disease (.i.e. immunization, drugs applications, etc.)

 

j) All of the relationships and findings should make biological and epidemiological sense.         

 

It is not necessary that the causative agent meets all the criteria. However, the more criteria that are met, the more likely the agent is the putative one.

 

12.2.1 Etiological triad

 

a) For causation of an infection disease is necessary that etiological agents penetrate in susceptible host body under given environment conditions. These three factors determinating infection diseases are called "etiological triad".

 

b) Etiological (infectious) agents must enter the susceptible organism in such a quantity (number, infectious doses) and with such properties that enable to provoke a specific disease. Following characteristics are of major importance:

 

-  host range (the wider the host range, the more capable the organism is of spreading and developing disease in animals)

 

-  ability to survive in the environment

 

-  infectivity (the ability of the etiological agent to infect and multiply; often related to dose and pathogenity)

 

-  pathogenity (the ability to produce pathologic changes or disease)

 

-  virulence (the degree of pathogenity and the ability to cause disease despite host defenses; a truly successful pathogen would not be so virulent that it would cause the death of its host and thus, itself).

 

-  other factors (see chapter 8).

 

b) Individual  host  factors   can   be   either   intrinsic (endogenous), i.e.  predetermined such as species, age,  breed or sex, or extrinsic (exogenous, environmental), i.e. can  be  manipulated  such  as  immunization   status, feed, contacts, use or  behaviour. (See chapter 2).

 

c) Environment factors such as climate, bedding, housing, hygiene etc. (see chapters 11 and 16) influence the interaction between etiological agents and host in positive or negative sense.

 

-  Predisposing factors are those that prepare, sensitize, condition, or otherwise create a situation such as a level of immunity or state of susceptibility so that the host tends to react in a specific fashion to a disease agent;

 

-  enabling factors are those that facilitate the manifestation of the disease, ill-health or conversely those that facilitate recovery from disease, maintenance or enhancement of health status;

 

-  precipitating factors are those that associate with the definite onset of a disease, illness, behavioural response, or course of action;

 

-  reinforcing factors are those tending to perpetuate or aggravate the presence of a disease, disability, pattern of behaviour or course of action. They may tend to be repetitive.

 

12.2.2 Portals of entry of etiological agents

 

a) Portal of entry  is the place through which etiological agents enters the macroorganism. Each of the species of these agents is characterized by a specific portal(s) of entry.

 

b) Digestive tract is for most etiological agents the most frequent portal of entry, in particular for alimentary - gastrointestinal infections (salmonellosis, infectious gastroenteritis, etc.).

 

c) Respiratory tract is the main portal of entry for respiratory pathogens of aerogenic infections (influenza, infectious laryngo-tracheitis, etc.).

 

d) Urogenital (reproductive) tract is the main portal of entry for venereal diseases (trichomoniasis of cattle, dourine, etc.).

 

e) Mammary gland (teat canal) is the portal of entry for different agents causing infectious mastitis (e.g. Streptococcus agalactiae).

 

f) Skin is the portal of entry of a series of etiological agents transmitted by bite (rabies), sting (tick-born diseases), wound (tetanus) or by simple contact (mycotic skin diseases).

 

g) Other portal of entry are umbilicus (umbilical infections) and conjunctiva (ocular infections).

 

h) However in many agents  the portal of entry may vary (Bacillus anthracis, Brucella abortus).

 

i) Accidental entry may occur through  human  interventions  such  as  use of  blood  contaminated  needles  or  other   equipment  to  spread blood‑borne pathogens (Anaplasma spp. infections).

 

12.3 Course of infection process

 

   The course of infection process depends on all three components of etiological triad. It has infinite variability. There are not two identical cases in absolute terms. Not always the course has all stages. The course can vary from very mild up to very severe (fatal) one.

 

12.3.1 Stages of infection process

 

a) Incubation period is the time interval between entry of etiological agents and appearance of the first sign or symptom of the disease in question. The duration, depending mainly on quantity and pathogenity of agents and host resistance, is very variable also in the same disease. Usually short incubation period is understood up to 7 days (e.g. in foot-and-mouth disease), medium length period one up to three weeks (e.g. piroplasmosis) and long period can be of months eventually years (e.g. brucellosis, tuberculosis).

 

b) Prodromal period is manifested by unspecific signs of infection process, like increase of body temperature, pulse and respiration rates, inappetence, etc. This stage usually corresponds with the penetration of etiological agents into blood stream disseminating them throughout the body (viraemia, bacteriaemia, bacillaemia, pyaemia, toxaemia, parasitaemia). Septicaemia means that the agents multiply in blood.

 

c) Manifestation period is characterized by specific clinical signs typical for a given infection. It corresponds to the period of localization of the agents and their toxins in particular tissues and organs.

 

d) Final period reflects the results of a given infection process:

 

   Convalescence means animal recovery and getting rid of the agents completely or not becoming asymptomatic carriers with the risk of disease recurrence (repeated flare-up). This happens mainly in animals with mild course of disease.

 

   Fatal result means the dead of affected animal and usually also of etiological agents inside of dead body. This happens mainly in animals with severe course of disease.

 

12.3.2 Forms of infection process according its duration

 

a) According to the duration of infection process following forms can be differentiated:

 

-  peracute when within a very short time, suddenly or within several hours up to few days after first clinical signs, the animal dies (e.g. peracute form of foot-and-mouth disease);

 

-  acute when clinical signs last from few days up to two weeks (e.g. acute form of foot-and-mouth disease);

 

-  subacute when clinical signs last from about two weeks up to one month (e.g. subacute form of rinderpest);

 

-  subchronic when clinical signs last few months (e.g. subchronic form of respiratory infection);

 

-  chronic when clinical signs last many months and years (e.g. chronic form of tuberculosis).

 

b) In many infection processes can be found all above mentioned forms of duration depending on particular etiological triad interaction.

 

c) Latent period is the delay between exposure to disease-causing agents and the appearance of manifestations of the disease and the duration of unapparent form.

 

12.4 Forms of infection process according its manifestation

 

a) Apparent form is clinical manifestation of the process which can be either typical (specific for the infection) or atypical (different from the typical form). Unfortunately, atypical forms very often represent the majority of cases.

 

b) Abortive form is characterized by clinical signs hardly to be noticed and disappearing relatively soon.

 

c) Unapparent (latent, subclinical, asymptomatic) form is the presence of infection process in a host without occurrence of recognizable clinical signs or symptoms. Unapparent infections are only identifiable by laboratory means. For disease propagation the most dangerous are animals with unapparent form harbouring etiological agents which can be eliminated or can cause a flare-up and spread of the disease if animal resistance is reduced.

 

b) In many infection processes can be found all above mentioned forms depending on particular etiological triad interaction.

 

c) Syndrome is a symptom complex in which the symptoms and/or signs coexist more frequently than would be expected by chance on the assumption of independence.   

 

d) "Iceberg effect". In many, mainly chronic diseases,  only a relatively small fraction of diseased animals can be detected clinically.

 

12.5 Classification of animal infections

 

   There are many criteria for animal infections classification which are being used separately or in combination of different views.

 

12.5.1 Classification according to hosts

 

   Classification can be according to:

 

-  zoological class, order, family, genus and species (e.g. cattle infections)

-  animal category (e.g. calves infections)

-  number of susceptible species (e.g. monohostal, polyhostal infections)

-  transmissibility to man (zoonotic infections)

-  transmissibility to new born animals (e.g. congenital infections, hereditary infections).

 

12.5.2 Classification according to etiological agents

 

   Classification can be according to:

 

-  biological criteria (e.g. viral infections, mycotic infections, helminthic infections)

-  origin of etiological agents (exogenous infections, endogenous infections - agents latently surviving inside the animal body; indigenous infections, exotic infections)

-  contagiousness (contagious infections, non-contagious infections)

-  quantity of agent species (monoetiological infections, polyetiological or multicausal infections)

-  agents participation order (primary infections, secondary infections)

-  interaction with the macroorganism  such as reinfections (repeated agents penetration), superinfections (additional agents penetration), subinfections (limited number of agents - infection doses), parainfections (caused due to other agent species supporting influence), autoinfections (caused by  conditionally pathogenic microflora of animal body), intercurrent infections (when animal already suffers from other pre-existing disease), recurrent infections (recidives - disease reappearance due to the same etiological agents after their unapparent survival in animal body).

 

12.5.3 Classification according to transmission ways

 

   Classification can be according to:

 

-  mechanism of transmission (e.g. aerogenic infections)

-  portal of entry (e.g. umbilical infections)

-  localization of agents (e.g. pulmonary infections).

 

12.5.4 Classification according to other aspects

 

   Classification can be according to:

 

-  course of infection process (e.g. latent infections)

-  course of epizootic process (e.g. enzootic infections)

-  space factors (e.g. autochthonous infections, tropical                infections)

-  consequences/importance (e.g. infections of obligatory             notification, internationally reportable infections)

-  role of man (e.g. iatrogenic infections related to                  veterinarian activity; nosocomial infections acquired in         veterinary ambulance or hospital).

 

12.6 Number of animal infections

 

a) The number of infection diseases is enormous. Practical veterinary medicine deals only with selected diseases of major biological, economic, public health and social importance. Internationally more than 140 specific diseases are monitored. If we take all known etiological agents species we can estimate their number in thousands, not considering their serological types and subtypes. The complexity of infection diseases number is multiplied by enormous number of animal species which can suffer from different etiological agents (number of known species is estimated 4500 in mammals and 8600 in birds). This contributes to infinite variability of infection processes.

 

b) For practical reasons only the species of agents and animals of major importance for human society and biosphere are the objects of professional service activities.

   

12.7 Non-infection disease process

 

a) Non-infection disease process is based on the interaction of abiotic etiological agents (see chapter 8), animals and environment forming etiological triad.

 

b) General principles described above for infection disease process are almost all applicable also for non-infection disease process.

 

c) The course, forms and duration of non-infection disease process are similar as in infection disease process.

 

d) Classification can be according to etiological agents, animal species, mechanism of penetration, localization (skin diseases, cardiovascular diseases), physiological functions (production diseases, reproduction diseases, metabolic diseases), etc.

 

 


 

 

13. EPIZOOTIC PROCESS

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13.1 Introduction

 

a) Epizootic process is a biological, dynamic and multifactorial phenomenon based on a complex and continuous interaction among animal  p o p u l a t i o n, etiological agents and environment (epizootiological triad).

 

   It is closely related to infectious process (chapter 12) based on similar interaction cause by biological parasitism, however at individual animal level only and not at population level as in case of epizootic process.

 

b) According to etiological agents these processes can be divided in infectious epizootic process caused by biological agents and non-infectious epizootic process caused by abiotic agents.

 

   (This chapter describes mainly the aspects of infectious epizootic process serving as the model for non-infectious one concisely described at the end of this chapter).

 

13.2 Contents of epizootic process

 

   Infectious epizootic process is based on the circulation of etiological agents in animal population creating so called "epizootiological chain".

 

13.2.1 Animal population participation

 

a) Animal population creates the ground on which epizootic process develops.

 

b) Animal population in confrontation with etiological agents reacts in defending and/or adapting way winning or losing. It tends to maintain or regain biological inter-species balance.

 

c) Animal population acts against the population of etiological agents as an integral and organic complex  (collective defense and/or adaptation) and not as a simple sum of individual isolated animals.

 

d) Epizootic process is influenced by animal population characteristics described in chapter 2. The population size, species and categories structures, horizontal and vertical movement and resistance / susceptibility levels belong among the main influences. The dynamics of host populations is reflected significantly in the dynamics of epizootic process.

 

e) According to participation of animal species the epizootic process can be divided in monohostal (including only one animal species) and polyhostal (including more than one animal species).

 

13.2.2 Etiological agents participation

 

a) Etiological agents search in animal hosts adequate conditions for their life, nutrition and reproduction using parasitic forms.

 

b) In order to keep their species existence the etiological agents need nutrition substances in continuing form. This is made possible through the circulation of the agents in respective animal populations using different ways of transmission to new host offering desirable conditions. Therefore continuity of epizootic process depends on horizontal and/or vertical circulation of etiological agents.

 

c) Particular epizootic process can be mono-etiological including only one species of etiological agents or poly-etiological including more than one species (up to etiological complex).

 

13.2.3 Environment participation

 

   Environmental (ecological) factors (see chapters 11 and 16) create conditions for the life and activities of animal populations as well as of etiological agents when outside of animal body and thus influences epizootic process. It represents also the medium in which etiological agents are transmitted from one host to the other one.

 

13.2.4 Epizootiological chain

 

a) Repeating and  continuing process of etiological agents transmissions between the susceptible hosts creates so called "epizootiological chain". Basic link (component) of epizootiological chain is the transmission from one to other individual host.

 

b) Etiological agents circulating from one host can find adequate conditions in or on new susceptible animal and prolong the process as continuing epizootiological chain or not and thus interrupting this chain.

 

c) Epizootiological chain can have different form such as:

 

-  linear (isolated and parallel)

-  divergent (double, multiple or star-shaped branches) 

-  convergent (double, multiple or star-shaped branches)

-  combined.

 

   Anazootic is a process where all cases have one common source of etiological agents.

 

d) According to the manifestation epizootiological chain can be:

 

-  apparent (hosts with clinical symptoms) which can be         divided in typical and atypical forms;

-  unapparent (hosts without any clinical symptoms) which can   be divided in subclinical (internal changes without clinical    manifestation) and latent (simple carriers) forms.

 

e) According host species participation epizootiological chain can be:

 

-  homogeneous when only one host species is involved (e.g. horse-horse-horse in glanders);

-  heterogeneous when more than one host species is involved  (e.g. sheep-cattle-goat in foot-and-mouth disease, horse-Glossina fly-cattle in trypanosomiasis caused by T.vivax).

 

f) Infinite combination exists in large epizootiological chains of polyhostal infections.

 

13.3 Course of epizootic process

 

a) Any epizootic process, similarly as any other biological phenomenon, has its origin, development and end. This course is influenced by all components of epizootiological triad and their characteristics.

 

b) In spite of extraordinary variability of epizootic courses, determinate regularity can be found in specific diseases under natural conditions.

 

c) Continuing epizootic processes under natural conditions develop in epizootic waves reflecting changes of triad components in space and time.

 

d) Epizootic stages and curves can be expressed in number (or proportion from total animals) of specific disease cases. The transition between individual stages is usually gradual without clear cut limits.

 

13.3.1 Stages of continuous epizootic process

 

a) Interepizootic stage is the period between postepizootic stage of epizootic wave and outset of specific epizootic process activation - preepizootic stage. Survived animal population from previous epizootic wave maintain elevated immunity and therefore no specific disease cases or only sporadic ones, mainly with atypical and chronic forms, can be detected. This stage is also called as latent, "sleeping", occult, of epizootic stability or tranquillity.

 

b) Preepizootic stage is the period between interepizootic and ascending stages. Population specific immunity gained during previous wave is reduced and number of susceptible animals is increased also due new born and introduced animals. Etiological agents increase in number and their pathogenity gets stronger. Sporadic specific disease cases mainly with atypical chronic manifest or subclinical forms can be detected. This stage is also called as awakening period.

 

c) Ascending stage is the period between preepizootic and culmination stages reflecting the most intensive part of epizootic process wave. Population specific immunity is nearing to minimum and number, pathogenity and propagation of etiological agents is nearing to maximum. Number of affected animals is increasing. At the beginning of this stage disease cases are more of atypical and abortive forms and later on are close to typical or typical not only clinically but also pathomorphologically. At the end clinical cases have the tendency to acute and peracute forms.

 

d) Culmination stage  is the period between ascending and descending stages reflecting relatively full biological development of epizootic process in a given wave. Population immunity is at minimal level and number, pathogenity and propagation of etiological agents are at maximal levels. At the beginning the cases are typical con tendency to acute form and later atypical cases increase gradually with tendency to subacute form and afterwards to milder course. Population immunity is getting slowly stronger thanks to animals surviving the disease (natural immunization) and this increasing barrier causes the reduction or slowing down of etiological agents activities and propagation.

 

e) Descending stage is the period between culmination and postepizootic stages. Proportion of naturally immunized animals is increasing while number of susceptible animals is decreasing gradually towards the minimum. Number, pathogenity and propagation of etiological agents is tending gradually towards the minimum. Number of diseased animals is gradually decreasing as well and the cases are getting more atypical, abortive up to subchronic and chronic forms meanwhile the proportion of latent carriers is increasing.

 

f) Postepizootic stage is the period between descending and interepizootic stages. Population immunity is very high, number, pathogenity and propagation of etiological agents fall to very low values up to relatively minimal ones. Number of diseased animals is reduced to sporadic (exceptional) cases. Latent forms in which  asymptomatic carriers prevail can be detected only using indirect diagnostic methods (serological, allergic, etc.).

 

13.3.2 Stages of new epizootic process

 

   In new continuing epizootic  process the above described stages under natural conditions are complemented by incubation and prodromal stages.

 

a) Incubation stage is the period between the onset of particular epizootic process and prodromal stage. Incubation stage in a given place occupies the period from the first moment of introduction (penetration) of first specific etiological agents in a given population, herds or flocks. The number of affected animals slowly increases without clinical manifestation.  Etiological agents, thanks missing population immunity, have the chance to reproduce and propagate increasing their pathogenity when passing through individual susceptible animals.

 

b) Prodromal stage is the period between incubation and ascending stages. The first diseased animals manifest general clinical and pathomorphological changes without specific characteristics. The number of these animals is increasing as well as the number, pathogenity and propagation of specific etiological agents.

 

13.3.3 Stages of terminating epizootic process

  

   In terminating epizootic  processes the above described stages under natural conditions are complemented by extinction stage following descending stage. It is the period in which epizootic process dies and become extinct. Susceptible animals gradually disappear, number, pathogenity and propagation of etiological agents go gradually down up to disappear in the given space and time.

 

13.4 Forms of epizootic process

 

a) Apparent or manifest forms can be divided in:

 

-  typical when clinical and epizootiological characteristics correspond with specific features

-  atypical in opposite cases

-  abortive when clinical and epizootiological characteristics are only mildly expressed (difficult to determine).

 

b) Unapparent (subclinical or asymptomatic) forms are without any clinical manifestation, however interaction between animal population and etiological agents takes place. Morphological and/or physiological changes can be typical corresponding with specific picture or atypical not corresponding with known specific picture.

 

c) Latent form when etiological agents are inside the animals-carries without pathogenic action.

 

d) Epizootic process forms are usually mixed i.e. composed of more than one of the above mentioned forms.

 

e) According the severity epizootic process can be malignant with serious consequences or non-malignant with mild consequences.

 

13.5 Range, intensity and grades of epizootic process

 

13.5.1 Population range of epizootic process

 

   Population range (width) of epizootic process is expressed by absolute number and proportion of affected animals (epizootiologically non-healthy)  e x i s t i n g  in one or more biological species in given place and time. This criterion can be expressed in prevalence of specifically affected animals. These values can vary from exceptional occurrence up to ubiquitous values.

 

13.5.2 Population intensity of epizootic process

 

   Population intensity of epizootic process is expressed by absolute number and proportion of  n e w  affected animals (epizootiologically non-healthy) of exposed population(s) at risk in given place and period. This criterion can be expressed in incidence of specifically affected animals. In local and short duration outbreaks attack rate can be used. Infection rate is the incidence of manifest plus unapparent infections, which can be identified, e.g. by serological testing.

 

   For decreasing intensity of epizootic process indicator of extinction of specifically affected animals can be used.  (See indicators in chapter 6).

 

13.5.3 Grades of epizootic process

 

a)  Grades of epizootic process (pattern of disease levels) is the outcome of combined values of range (width), intensity, propagation, tendency as well as space and time factors of particular disease. Every disease has determinate tendency regarding the grade of epizootic process.

 

    The bellow division is only artificial framework for epizootic process classification. There are also transition grades such as hypo-, meso- and hyper- grades (e.g. hypo-enzootic). Almost in all infectious disease all mentioned grades can be found according to different conditions. These grades have important role in defining control strategy and measures.

 

b) Sporadic cases occur irregularly, haphazardly from time to time, and infrequently (e.g. anthrax).

 

c) Enzootic (endemic in human epidemiology). The specific disease or infectious etiological agents are continuously present in a given population or geographical area during years, decades, eventually centuries, etc. It may also refer to the usual prevalence of a given disease within such area or group.

  

   Hyper-enzootic disease is constantly present at a high incidence and/or prevalence rate with a persistent intense transmission.

 

d) Epizootic (epidemic in human epidemiology) is the occurrence in a population or region of cases of a disease clearly in excess of normal expectancy, i.e. in relation to usual frequency of the disease in the same area, among the specific population, at the same season of the year. The number of cases indicating the presence of an epizootic varies according to the agent, size, and type of population exposed, previous experience or lack of exposure to the disease, and time and place of occurrence.

 

   Epizootic includes also a level of disease that occurs suddenly in excess of the normal enzootic level in a population, herd or geographical area as well as new outbreaks in previously free territory.

 

   Point epizootic is the process in which the disease requires sudden fast and efficient mode of transmission, that does not spread further, and is due to a common exposure. (E.g. mycotoxic infection due to contaminated feed centrally distributed to grand number of animals).

 

   Propagated epizootic requires a less efficient mode of transmission and shows a pattern of spread from one animal to another. This disease usually involves vectors or carriers.

 

e) Panzootic (pandemic in human epidemiology) is a process occurring over a very wide area and usually affecting a large proportion of the population. Panzootic wave can cross countries and continent . Panzootic process can be rapid propagating over large territories in a very short time (e.g. panzootic waves of foot-and-mouth disease) or slow propagating over large territories during long period (e.g. myiasis due to screwworm fly).

 

f) Mixed grades reflect the situation when and where in the same space and time can one grade be combined with the other one (e.g. enzoo-epizootic when in enzootic area an epizootic appears).

 

13.6 Space aspects and epizootic process

 

a) Location. It is obvious that epizootic processes are located in areas (nosoareas) with susceptible species of animals.

 

b) Some epizootic processes are located in particular regions (e.g. Venezuelan equine encephalomyelitis in South America) due to specific environmental conditions or other particular influences such as geographic isolation (islands).

 

c) Every epizootic process has its concrete localization and delimitation which can be identified using natural (geoecological) or artificial criteria (topographical, social/economical or political/administrative).

 

d) Spacial range (width) of epizootic process expresses the absolute size and proportion from the total territory using surface measure units (e.g. km2) or administrative units. Maps are usual means for evaluation of territorial occurrence of diseases.

 

e) Spacial intensity of epizootic process expresses concentration (density) and dispersion of affected animals in a given space or territory. The evaluation is based on the relation of the number of affected animals per surface measure unit. In many epizootic processes there is a tendency to space clustering of affected animals and foci.

 

f) Geographical distribution of epizootic processes can be universal (ubiquitous) occurring in the whole world (e.g. toxoplasmosis) or in limited territories at different levels (e.g. glanders in Central Asia).

 

g) According to different criteria the geographical distribution can be subdivided in so called "epizootiological zones" such as:

 

-  according to epizootic process course (e.g. zone of culmination stage)

-  according to epizootic process form (e.g. zone of manifest forms)

-  according to epizootic process grade (e.g. zone of sporadic cases, enzootic zone)

-  according to epizootic process type (e.g. zone of sylvatic rabies).

 

h) Epizootic processes are in permanent dynamic (mobility, changes) and only in relative stability not only as far as their characteristics are concerned but also regarding space aspects. Their horizontal movements are characterized by direction, speed , distance and frequency.

 

i) The spread of a disease can be towards different relatively separated places - dissemination form or step by step covering major and major area - propagative form.

 

13.7 Time aspects and epizootic process

 

a) For time delimitation of epizootic process critical points are origin and final moments of this process as well as origin and final moments of different stages and waves.

 

b) From the global point of view epizootic processes are uninterrupted (continuous epizootiological chain) up to the moment of their global extinction. Duration of these processes can be of hundreds and thousands years. In spite of the interruption of overwhelming majority of epizootiological chains (effective eradication programmes in different territories) converted in "blind branches", the particular processes continue (up today no one known animal disease has been globally eradicated). On the other hand it can be supposed that many diseases disappeared naturally in the past.

 

c) From the local point of view epizootic process duration is very different depending on many factors. In small foci immediately liquidated the process can be of up to several days and in grand foci can last many days (when liquidated), many weeks, months, years (e.g. enzootic) and centuries (e.g. in diseases with natural nidality).

 

d) In a given place or territory specific epizootic process can occur only once (exceptionally) or repeatedly (newly introduced) or in continuous form (including the recurrence based on new manifestation of previously latent course).

 

e) Periodicity of epizootic process is based on regular waves in disease occurrence - number of affected animals and foci. It has different forms such as:

 

-  seasonality with regular variation during the year that conforms to a regular seasonal pattern (e.g. typical for vectorial diseases with natural nidality);

-  cyclicity with regular variation during periods longer than one year (e.g. dependency on population immunity levels variation and vectors biology; 7-10 years cycles of foot-and-mouth disease in cattle under natural conditions).

 

f) Cases may occur in time clusters, a pattern typical of outbreaks or epizootic.  A useful means to represent the temporal distribution pattern of disease events is to construct an epizootic curve which can illustrate both the magnitude of the problem, i.e. the number of new cases occurring, and the rapidity with which the epizootic progresses.

 

13.8 Dynamics of epizootic process

 

   The dynamics of epizootic processes  is  caused and influenced  by  a  large  complex  of  changing  factors  such as characteristics of animal populations, etiological   agents, vectors populations and  environmental conditions as well as preventive and control measures. Infinite variability of the characteristics of these factors and their interactions conduce to infinite dynamics features of epizootic processes.

 

13.9 Classification of epizootic processes

 

   Classification of epizootic processes can be divided according to similar criteria as described in chapter 12. Other criteria are according to epizootic process course (stages), according to space and time aspects as described above.

 

13.10 Epizootic process of non-infectious diseases

 

a) Epizootic process of non-infectious disease is based on interaction between  a b i o t i c  etiological agents (factors) under given environmental conditions (non-infectious etiological triad) which is reflected in the content, course, forms, intensity, grades, dynamics as well as in space and time characteristics.

 

b) Majority of general principles applied in infectious processes are applicable on non-infectious processes.

 

c) It is obvious that these processes are relatively simpler due to the fact that abiotic etiological agents are unable to reproduce and continue through epizootiological chains as in case of infectious diseases.

 

d) Genetic diseases transmission to other generation represent a form of genetic chain. Short nutritional chain is known in some diseases caused by feed residues which can pass to man through food of animal origin.

 

 

 


 

 

14. ANIMAL POPULATION DISEASE NIDALITY

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14.1  Introduction

 

a) Nidality is the characteristic of etiological agents to occur in distinct nidi associated with particular geographic, climatic and ecological conditions.

 

b) Animal population disease nidality reflects the heterogeneity in territorial distribution of diseases based on places with concentrated sources of etiological agents - foci.

 

c) Focus (nidus) of animal disease (infection) is a place (area) with affected animals and/or other concentrated sources of specific etiological agents. The term is usually applied to a relatively small area in which  occurrence and spread of an infectious disease take place.

 

d) Very often the term "outbreak" is used as the synonym of "focus". Outbreak is an identified occurrence of disease involving one or more animals. It means an occurrence of the disease in an agriculture establishment, breeding establishment or premises, including all buildings and all adjoining premises where animals are present. For each disease the definition should be adjusted to its nature and given conditions.

 

e) Etiological agents  can be propagated from the foci to other places (areas) and thus facilitating continuation of epizootic process.

 

f) Territorial occurrence of animal diseases is the subject of so called "landscape epizootiology".

 

14.2  Foci according etiological triad components

 

a) Foci according participating etiological agents can be

divided in:

 

-  foci of specific disease (species of agents)

-  foci of specific disease types or subtypes

 

-  monoetiological (formed by only one agent species)

-  polyetiological (formed by more than one agent species).

 

b) Foci of specific disease can be divided according animal population participation in:

 

-  foci of the disease in particular animal species

-  foci of the disease in particular animal category

 

-  monohostal (only one animal species involved)

-  polyhostal (more than one animal species involved)

 

-  foci with affected animals

-  foci without affected animals (e.g. in observation period)

-  foci without any susceptible species animal (depopulated)

 

-  non-natural (man-made in domestic animals)

-  natural

-  combined (natural mixed with non-natural).

 

14.3  Foci according to their form

 

   Foci of specific disease can be divided according their forms in:

 

-  apparent or manifest with clinical manifestation

-  abortive manifestation without specific characteristics

-  latent without clinical manifestation

 

-  typical corresponding to usual specific characteristics

-  atypical not corresponding to specific characteristics

 

-  active with epizootic process spreading

-  non active (e.g. in interepizootic stage)

 

-  autochthonous originated without man's intervention

-  anthropurgic originated with man's intervention.

 

14.4  Foci and space aspects

 

a) Foci of specific disease can be divided according space factors in:

 

-  grand (can be divided in subfoci, e.g. ranch size in farm size)

-  small (if very close they can be united in one of major size)

 

-  with demarcated borders (clear cut limits separating from perifocal area)

-  with diffused borders (not clear limits)

 

-  elemental (with more intensive epizootic process inside of major focus, e.g. in natural nidi).

 

b) Geographic distribution is of an extraordinary importance. The same values of nidality rates and/or characteristics of particular foci have different epizootiological importance according their localization in relation to susceptible species distribution, exposition degree, ecological conditions, epizootiological situation, etc.

 

14.5  Foci and time aspects

 

a) Time delimitation of foci, mainly the moments of their origin and fin, indicates critical moments for diagnostic and control activities.

 

b) Foci of specific disease can be divided according time factors in:

 

-  primary, i.e. the first focus in a given area or territory; this criterion is relative (e.g. the same focus can be a primary one for a particular region but not at national level)

-  secondary following the primary one

 

-  of short duration (e.g. in peracute form of a disease)

-  of long duration (e.g. in chronic diseases)

 

-  new (fresh - e.g. primary focus)

-  old (residual - e.g. enzootic).

 

c) Frequency of new foci is expressed by incidence indicator.

 

d) Stages of foci are similar as the stages of epizootic process (see chapter 13).

 

14.6  Natural nidality

 

14.6.1 Concept of natural nidality

 

a) Natural nidus (focus) is the area of a particular biocoenosis in which etiological agents circulate independently on man.

 

b) Natural nidus is determinated biologically (influenced by the flora and fauna of host and vectors), geographically and ecologically (e.g. by the climate causing seasonality).

 

c) Bioceonotic relations among participating species are mainly of trophic (alimentary) character. These interrelations ensure uninterrupted transmission of etiological agents from wild animals-carriers to other susceptible animals (receptors) through vectors, eventually by other ways.

 

d) The animal-receptor converts in potential donor of etiological agents starting a new cycle of transmission and thus keeping their circulation and continuation of epizootiological chains through repeating cycles.

 

e) Also domestic animals, eventually human beings can be infected after entering in the area of natural focus and become receptors. Usually this branch of epizootic chain is blind and does not continue.

 

f) Natural nidi are characterized by typical enzootic grade of the process.

 

14.6.2 Circulation of etiological agents

 

a) Vectorial circulation of etiological agents is based on the transmission by vectors, mainly blood sucking arthropods, from animal-donors being in stage when these agents are spread in blood or in accessible tissue (e.g. role of ticks in tularemia). Vectorial transmission through vectors - non arthropods is based on their active penetration in  or being ingested by animal-receptor.

 

b) Avectorial circulation of etiological agents is based on direct transmission from one host to other host without any vectors (e.g. leptospirosis).

 

c) Mixed circulation of etiological agents combines vectorial and avectorial transmission (e.g. Q-fever).

 

d) Circulation of etiological agents among wild animals only constitutes so called wild cycle (sylvatic cycle) unlike domestic cycle among domestic and synanthropic animals (e.g. sylvatic and domestic cycles in many diseases with natural nidality such as rabies).

 

e) Some birds constitute reservoirs of different etiological agents of diseases with natural nidality (e.g. pheasants in equine encephalitis).

 

14.6.3 Biotic structure of natural foci

 

a) Biotic structure of natural foci is composed by following components:

 

-  etiological agents (pathoergonts)

-  animals-reservoirs (donors)

-  vectors (transmitters) in case of vectorial circulation  

-  animals-receptors

-  environment factors.

 

b) If more species participate in the circulation of etiological agents then biotic structure is richer and more complex.

 

c) Biotic structure is the phenomenon which keeps natural foci very resistant against different disturbances including control measures.

 

14.6.4 Territorial structure of natural foci

 

a) Natural foci territorial structure is composed from focal nucleus (elemental focus - focal "heard"), marginal area (around focal nucleus) and dispersion area (around marginal area).

 

b) In focal nucleus the epizootic process is the most active, consistent and lasting during existence of a given natural focus. Etiological agents spread from this area towards other focal areas often in form of waves. In this area the density of focal populations (hosts, interhosts and vectors) is high and epizootic process has hyper-enzootic character.

 

c) In marginal area the epizootic process has more hypo-enzootic character being refreshed by new waves of etiological agents propagation from focal nucleus.

 

d) In dispersion area the epizootic process is manifested mainly by sporadic cases of atypical course.

 

e) The borders between different components of natural foci are not clear cut and fixed due to their dynamics in space and time.

 

14.6.5 Biotopes changes and natural foci

 

a) Natural foci and their characteristics are closely related to biotopes and biocoenoses and their changes. Natural foci exist not only in purely natural biotopes but also in biotopes modified by human activities.

 

b) Human activities can activate some natural foci, change their characteristics, create unconsciously new ones or contribute to their disappearance. Disturbances of original biocoenoses can push the animals and vectors to search for new areas or to adapt themselves to the new conditions.

 

c) According to grade of land cultivation following biotopes can be distinguished:

 

-  natural (with original flora and fauna)

-  poorly cultivated (isolated culturcoenoses within the natural ones)

-  moderately cultivated (natural and cultivated areas mosaic)

-  highly cultivated (cultivated area is dominant)

-  totally cultivated.

 

14.6.6 Wild animals and natural foci

 

a) All animal species can participate in different natural foci of infectious disease: mammals, birds, reptiles, amphibians and fishes.

 

b) Wild animals according to their relation to man can be divided in exoanthropic living freely and far from human activity and in synanthropic living closely to man. The latter can be subdivided in permanent synanthropic (e.g. Mus musculus) and semipermanent synanthropic (e.g. Apodemus sylvaticus) living or penetrating in areas with domestic animals and human population.

 

c) Migratory and semipermanent animals have important role in creating new natural foci in distant territories.

 

14.6.7 Disease with natural nidality

 

   Almost all known infectious diseases can occur in form of natural foci. Examples:

 

-  viroses (Rift Valley fever, rabies)

-  bacterioses (pasteurelloses, tularemia)

-  chlamydioses and rickettsioses (Q-fever, cowdriosis)

-  mycoses (aspergillosis, actinomycosis)

-  protozooses (babesiosis, trypanosomiasis)

-  helminthiases (trichinellosis, fascioliasis)

 

14.7 Indicators of animal disease nidality (focality)

 

a) Nidality (focality) in quantitative terms expresses the grade in which a given territory is affected by specific infectious disease foci. The first step is to define clearly the limits and size of foci (individual diseases require different definitions) in order to be able to apply respective measure units.

 

b) As measure units can be used  surface measure units (e.g. km2) in natural foci or focal measure units such as production units (stables, farms, ranches), villages, districts, etc. in other foci.

 

c) For territorial distribution maps including not only "normal" foci but also artificial foci (e.g. sanitary slaughterhouses, laboratories working with infectious etiological agents, etc.) are used.

 

d) Nidality (focality) is the basic indicator expressing the relation of the number of foci to the total number of focal units; in natural nidality expressing the proportion of affected territory size from the total territory.

 

e) In concrete cases of specific diseases is necessary to respect time factors:

 

-  moment prevalence rate of foci

-  period prevalence rate of foci

-  average prevalence rate of foci

 

-  incidence rate of foci

-  extinction rate of foci

 

   Note: More information on the indicators see in chapter 20.

 

f) Other indicators used are the rates of affected farms, epizootiological zone rates (e.g. rate of affected zone), territorial density of foci, etc.

 

14.8 Nidality of non-infectious diseases

 

a) Also non-infectious diseases can occur in distinct nidi associated with particular ecological conditions reflecting the heterogeneity in territorial distribution of these diseases (e.g. plant toxicoses, alimentary deficiencies).

 

b) In spite of the fact that the nidality mechanism is completely different in comparison with infectious diseases, many aspects and methods described above are applicable on non-infectious diseases as well.

 

Note:

 

    Landscape epizootiology (syn.: epizootiological ecology, horizontal epizootiology, epizootiological geography, etc.) is founded on the concept that if the nidality of diseases is based on ecological factors then a study of ecosystems enables predictions to be made about the occurrence of disease and facilitates the development of appropriate strategy.

 

 

 


 

 

15. DISEASES COMMON TO MAN AND ANIMALS

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15.1 Introduction

 

a)  Man and animals have shared the same environment throughout their evolution. It is consequently natural that they share many pathogens. Because of this closeness, some parasitic organisms have developed life cycles which may include animals as well as man; others have adapted themselves so as to accept man (or, viceversa, animals) as an occasional host, not essential for the survival of the parasite species.

 

b) Those diseases and infections that are naturally transmitted between vertebrate animals and man are defined as zoonoses.

 

c) There are two groups of communicable diseases common to man and animals:

 

aa) Zoonoses represent infections or infectious diseases transmissible under natural conditions from vertebrate animals to man where animals play an essential role in maintaining the infection in nature and man is only an accidental host.

 

bb) Diseases where both man and animals contract the infection from the same sources, such as soil, water, invertebrate animals and plants; as a rule, however, animals do not play an essential role in the life cycle of these etiological agents, but may contribute in varying degrees to the distribution and actual transmission of infections.

 

d) Due the fact that Homo sapiens  belongs biologically to animal kingdom (mammals class) many general principles of epizootiology are applicable on human epidemiology and vice versa. This is the reason why epizootic and epidemic processes are so similar and in zoonoses are commune. However, social/community and creative consciousness aspects significantly differentiate human beings from animals with all consequences for communicable diseases processes.

 

e) Majority of the known infectious diseases in human population has historical or actual relation to animal diseases.

 

f) When zoonotic disease are occurring at a low incidence, the occurrence of human disease my often be the first indication that infection is being transmitted (e.g. chlamydiosis - psittacosis in slaughterhouse employees from infected  turkeys).

 

15.2 Human population and its basic characteristics

 

  For epidemic processes of diseases common to man and animals following characteristics of human population are of major importance:

 

- absolute numbers of inhabitants (demography)

- geographical distribution

- density and concentration

- relations between number of inhabitants and animals

- category (age, sex, etc.) structures

- living standard

- economic and social activities

- culture life

- horizontal movement

- reproduction (much slower than in animals)

- disease resistance and susceptibility, etc.

 

15.3 Exposition of human population

 

a) Exposition to common etiological agents  can be direct or indirect. It is obvious that rural population is more exposed to diseases transmissible from affected domestic animals than urban population. Particular zoonotic risk is there where humans and domestic animals live under the same roof in daily contact between them.

 

  Inhabitants are at zoonotic risk when consuming crude food of animal origin.

 

b) Wild synanthropic animals (e.g. wild rodents such as rat and mouse) living in the same areas as humans and having access to stored food represent other type of risk.

 

c) Professional exposition during human activities in risky environment such as livestock husbandry, slaughterhouses, diagnostic and production laboratories, etc. causes many cases of occupational zoonoses among farmers, workers, veterinarians, etc.

 

d) Recreational exposition of tourists, hunters etc. in territory with natural nidality diseases represents the risk  of acquiring local infections.

 

15.4 Sources of common etiological agents

 

a) Primary sources are diseased (affected) animals from which etiological agents can be transmitted to man directly and/or indirectly (e.g. B. melitensis). In some zoonoses also man can become primary source threatening humans and susceptible animals (e.g. Taenia saginata). In majority of zoonoses man has the role as final or accidental host.

 

b) Vectors as intermediatory sources and transmitters play similar role in human as in animal populations (e.g. ticks in Q-fever).

 

c) Food of animal origin if infected and/or contaminated represents secondary source of many zoonotic etiological agents causing alimentary infections in humans (e.g. milk in brucellosis, meat in salmonelosis).

 

d) Soil, water and other contaminated substances and objects can serve as sources of zoonotic etiological agents threatening human beings (e.g. B.tetani).

 

e) Biological products containing live zoonotic etiological agents such as laboratory strains (e.g. B.mallei), live vaccines (e.g. anti-brucellosis vaccine B 19), etc. have caused specific diseases in humans.

 

15.5 Transmission of common etiological agents

 

a) Forms of transmission of etiological agents common to man and animals are similar as described in chapter 10. This is valid not only for the transmission from animals to man but also from man to animals. Interhuman transmission of zoonoses is usually limited to exceptional cases, if any. However, interhuman transmission of cutaneous zoonotic mycoses can be quite frequent.

 

b) Particular form of transmission is in case when man participates in life cycle of some zoonotic parasites(e.g.transmission of Taenia saginata to cattle through ingesting eggs from faeces of man affected by adult forms).

 

15.6 Infections common to animals and man

 

15.6.1 Classification of zoonoses

 

   Classification of zoonoses has different criteria. As example following subdivision is used:

 

a) Direct  zoonoses: Infections  perpetuated in a host and transmitted to humans either directly by a bite (e.g.rabies) or indirectly by contamination of human food (e.g. Salmonella   contamination of meat).

 

b) Cyclozoonoses: More than one vertebrate species are required for survival (e.g. hydatid disease due to Echinococcus granulosis depends on both a canid and ruminant for survival).

 

c) Metazoonoses: These zoonoses require both a vertebrate and an invertebrate host for survival. Humans are infected  when  bitten by   vector species (e.g. viral  encephalitis survives in various avian species and transmission is achieved by  mosquitoes).

  

d) Saprozoonoses:  These  infections require  a  non‑living site such as soil or water to persist or  multiply.  Both parasitic (e.g. visceral larval migrans) and mycotic (e.g.  blastomycosis) zoonoses fall into this group.

 

15.6.2  Examples of diseases common to man and animals:

 

a) Viroses: Argentine haemorrhagic fever, Bolivian haemorrhagic fever, bovine papular stomatitis, California encephalitis, cat-scratch disease, Colorado tick fever, contagious ecthyma, cowpox, Crimean-Congo haemorrhagic fever, eastern equine encephalitis, encephalomyocarditis, fevers caused by group of C arboviruses, foot-and-mouth disease, goatpox, haemorrhagic fever with renal syndrome, hepatitis transmitted by non-human primates, herpes simplex, Herpesvirus simiae, Ilheus fever, influenza, Japanese B encephalitis, jungle yellow fever, Kyasanur forest disease, Lassa fever, louping ill, lymphocytic choriomeningitis, Marburg disease, Mayaro fever, Murray Valley encephalitis, Newcastle disease, Omsk haemorrhagic fever, Pawassan encephalitis, pseudocowpox, rabies, Rift Valley fever, rotaviral enteritis, Russian spring-summer encephalitis, St.Louis encephalitis, Sindbis fever, smallpox of non-human primates, swine vesicular disease, vaccinia virus infection, Venezuelan equine encephalitis, vesicular stomatitis, Wesselsbron disease, western equine encephalitis and West Nile fever.

 

b) Bacterioses: Erysipelas (human erysipeloid), animal tuberculosis, anthrax, botulism, brucellosis, campylobacteriosis, clostridial food poisoning, clostridial wound infections, colibacillosis, glanders, leptospirosis, listeriosis, melioidosis, pasteurellosis, plague, rat-bite fever, salmonellosis, shigellosis, staphylococcal food poisoning, streptococcosis, tetanus, tick-borne relapsing fever, tularemia and yersiniosis.

 

c) Mycoses: actinomycosis, adiaspiromycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, cryptococcosis, dermatophylosis, dermatophytosis, histoplasmosis, maduromycosis, nocardiosis, phycomycosis, rhinosporidiosis and sporotrichosis.

 

d) Chlamydioses and rickettsioses: Asian ixodo-rickettsiosis, boutonneuse fever, flea-borne typhus fever, fowl chlamydiosis, Q-fever, Qeensland tick typhus, rickettsial pox, Rocky Mountain spotted fever and scrub typhus.

 

e) Protozooses: African trypanosomiasis, American trypanosomiasis, babesiosis, cutaneous leishmaniasis, malaria in non-human primates, pneumocystis pneumonia, toxoplasmosis and visceral leishmaniasis.

 

f) Metazooses:

 

aa) Trematodiases: clonorchiasis, dicroceliasis, echinostomiasis, fascioliasis, fasciolopsiasis, gastrodiscoidiasis, heterophyiasis, opistorchiasis, paragonimiasis and schistosomiasis.

 

bb) Cestodiases: Bertielliasis, coenurosis, diphyllobothriasis, dipylidiasis, hydatidosis, hymenolepiasis, inermicapsiferiasis, mesocestoidiasis, raillietiniasis, sparganosis and taeniasis.

 

cc) Nematodiases: Angiostrongyliasis, anisakiasis, ancylostomiasis, ascariasis, capillariasis, cutaneous larva migrans, dioctophymosis, dracontiasis, esophagostomiasis, gnathostomiasis, lagochilascariasis, strongyloidiasis, syngamosis, thelaziasis, trichinosis, trichostrongyliasis, toxocariasis and zoonotic filariasis.

 

dd) Pentastomids and arthropods: myiases (including screwworm fly Cochlyomyia hominivorax), pentastomidiasis, tungiasis and zoonotic scabies.

 

 

  

   Note: More information in human epidemiology textbooks.

 

 


 

 

16. ECONOMIC AND SOCIAL FACTORS INFLUENCING EPIZOOTIC PROCESS

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16.1 Introduction

 

a) Epizootic process is influenced not only by natural environment but also by economic and social factors. All these factors act individually or in complex, positively or negatively, directly or indirectly.

 

b) Economic and social factors analogically as natural environmental phenomena can influence animal population, etiological agents and their transmission. Therefore these factors play very important role in epizootiological situation development.

 

16.2 Influences of economic factors

 

16.2.1 Influences of economic level

 

a) Total national and per capita crude product reflected in social level and in availability of material and financial resources for animal health programmes influences epizootic processes indirectly.

 

b) Better conditions for the origin and development of epizootic processes are in territories with low economic level or in economic crisis where due to shortage of economic resources epizootiological situation cannot be controlled effectively or at all and vice versa.

 

c) Animal health programmes of poor countries have serious shortage of funds, professional manpower, diagnostic laboratories, transport, equipment, drugs and vaccines combined with underdeveloped communication, infrastructure, investment and suffering by high inflation. Under these conditions it is very difficult to carry out effective animal health actions. Opposite situation is in rich developed countries.

 

d) International technical assistance supporting national programmes is important, however it can only help for relatively short period but cannot fully replace national funding, manpower and infrastructure.

 

16.2.2 Influence of urbanization and industrialization

 

a) Urbanization aggregating human populations in cities creates new conditions for epizootic processes due to changed ecosystems and urban and suburban biocoenoses. It facilitates isolation of domestic animals from wild animals as well as separation between circulation of etiological agents in urban and wild (sylvatic) cycles (e.g. rabies).

 

   Other impact of urbanization is isolation of domestic animals kept individually slowing eventual disease propagation. However, stray animals in cities are becoming serious problem in controlling diseases, zoonoses in particular.

 

b) Industrialization forms areas without or almost without domestic animals. However synanthropic animals are able to adapt and survive.

 

c) Urbanization and industrialization change significantly landscape, climatic, hydrologic and biospheric conditions with usually negative impact on animal populations, their health and resistance. Control of animal population diseases is very distinct in comparison with rural areas.

 

16.2.3 Influences of transport, trade and tourism

 

a) Transport in general and in particular of animals and their products facilitates propagation of etiological agents at local, regional, provincial, national and international levels. Today transport means are able to reach any place in the world in very short time which can intermediate rapid propagation of animal diseases to very distant places. Increasing transport intensity increases the risk to introduce exotic diseases into free territories. In principle, any import of animals and their crude products represents epizootiological risk. The most dangerous are animals - latent carriers (without clinical symptoms) and their products  certificated as healthy.

 

b) Trade routes and market places imprint the framework for many infectious diseases and their propagation (e.g. massive territorial spread of foot-and-mouth disease from cattle market place where few latently diseased animals from one focus were introduced). Intensification of trade and its vertical and horizontal networks increases epizootiological risk. The traders do not always respect veterinary measures and many try to cheat to save the profit.

 

   Movement of animals is often associated with disease outbreaks. Therefore  the history  of  recent  exposure  through marketing channels requires that purchasing policies be evaluated.

 

c) Increasing tourism increases the risk of animal diseases propagation  through wastes of crude food of animal origin used for personal consume or of zoonotic diseases (parasites) where the man is final host or interhost (e.g. invasion of cattle ingesting grass contaminated by human faeces with eggs of Taenia saginata in tourist camping zone).

 

16.2.4 Influences of rural development

 

   Rural development based on transformation of rural activities and conditions tending to improve agriculture production using new technologies, irrigation, drainage, building dams, roads, communication networks etc. changes land use, rural ecosystem and biocoenosis. This has impact on epizootiological situation development (e.g. irrigation facilitates origin and propagation of  mosquito-borne diseases).

 

16.2.5 Influences of economic activities

 

   Economic activities not respecting animal health reduce the resistance and thus contribute to worsening of animal population health. Among the factors altering original ecosystems are pollution of different types (physical, chemical and biological), destruction and deterioration of environment, contamination of soil, water, feeds, etc. Use of chemicals in agriculture causes the problems of residues in animal products.

 

16.3 Influences of animal breeding and production

 

16.3.1 Grade of animal breeding and production development

 

a) Breeding and production systems influence directly and indirectly epizootic processes and epizootiological situation:

 

b) Primitive natural animal breeding where etiological agents circulate freely among domestic and wild animals due to lack of their mutual isolation mainly in vast pasture territories is very favourable for epizootic processes development and on the other hand is very difficult to control them (e.g. rinderpest in nomadic cattle herds). Natural resistance of local breeds is relatively high. Parasitoses can be found almost in all adult animals. Vectorial diseases are relatively frequent.

 

c) Extensive systems of raising livestock is characterized by animals being free within the defined area of natural pastures. Animals are relatively dispersed and therefore specific epizootic processes propagate slowly and within the area of pasture limit (if there are not contacts with neighbouring domestic animals or wild animals of susceptible species).

 

d) Intensive breeding and production is based on major concentration of domestic animals isolated from neighbouring herds and wild animals. Eventual epizootic processes have easier conditions for local propagation within affected herds and more difficult conditions for propagation to other livestock husbandry establishments. Intensive raising include also grazing either crops or cultivated pastures.

 

e) Industrial type of production characterized by high animal concentration, specialization and yielding facilitates the protection against the introduction of etiological agents from outside due to complex isolation. On the other hand in case of infectious disease outbreak the propagation is relatively easy and speedy thanks also to many passages of etiological agents conducing to higher pathogenity. Natural resistance is low and stress factors due to artificial conditions can contribute to the origin of endogenous diseases.

 

f) Pathogen free breeding based on parturition and keeping of animals under artificial conditions without etiological agents represent the most developed form of animal industry. These animals are highly susceptible to different diseases and require perfect protection.

 

g) The above classification represent only an orientation structure. There are many mixed and transition forms.

 

16.3.2 Organization and structure of breeding and production

 

a) Organization and structure imprint the framework for eventual epizootic processes and epizootiological situation.

 

b) Horizontal (decentralized) type of organization according to territories can facilitate disease propagation among different establishments in a given region.

 

c) Vertical (centralized) type according to specialized breeding and production can facilitate disease propagation between different territories, including distant places linked in production and category specialized units chain (e.g.calves - heifers - cows - feedlot units).

 

d) Organization according to production sectors (private, cooperative, state, etc.) creates other structure having also particular impact on epizootiological situation.

 

e) Similar role has internal organization and structure of individual establishments (farms, ranches, etc.).

 

16.3.3 Animal breeding and production technology

 

a) There are many different technologies. Each of them has different importance for animals, animal health and disease and for etiological agents transmission. Therefore each technology requires particular evaluation from epizootiological point of view to protect animals and to apply necessary measures in case of an outbreak.

 

b) The availability of and type of housing for  animals either complete or intermittent can have  very significant effects on disease occurrence either by increasing the density of animals or as a result of air quality. The type of flooring and bedding may influence the surviving of etiological agents eliminated by affected animals. Contaminated facilities  for feeding,  watering, and maintaining hygiene can have similar role.

 

c) Physiological deficiency and contamination of breeding and production mechanization equipment can hurt or cause stress and provocation of endogenous diseases or facilitate transmission of some etiological agents (e.g. mastitis through contaminated machine milking).

 

d) Central preparation and distribution of feed if contaminated can cause the spread of alimentary diseases.

 

e) Genetic crossing and selection, in particular of males for mating (artificial insemination), if health aspects are underestimated and affected animals are used, can cause dissemination of infectious diseases (e.g. venereal) to many females in the given area.

 

f) Reproduction system has the influence on vertical transmission of etiological agents to new generation. New born animals breeding technology is decisive for later development and health depending a lot on duration of contacts between the mother and young animals. There are different technologies from semi-natural up to artificial breeding (shortening and/or eliminating these pre-weaning contacts).

 

g) Breeding and production space and time cycles and rhythms reflect in eventual epizootic processes cycles and rhythms. This is valid also for technology synchronization influences.

 

16.3.4 Management and hygiene influences

 

a) Many different techniques are used to manage animals particularly under intensive production systems. These include  segregation of species, "all in‑all out" policies whereby  housing is completely cleaned and disinfected between groups  of animals, or continuous flow systems where no attempt is made to segregate animals by age or state of production. If infectious agents are introduced then in "all in-all out" system the transmission to following "batch" is avoided which is not the case in continuous flow system.

 

b) Similar difference in the consequences can also be between "closed" (self-sufficient) and "open" (supplied by animals from outside) herds or flocks.

 

c) Methods of feed and water delivery, as well as the sources, storage and pattern of feeding  play a role in eventual transmission of infectious agents penetrating through oral portal of entry.

 

16.3.5 Processing of products of animal origin

 

   Facilities processing products of animal origin from places of different epizootiological situation must be understood as artificial foci of etiological agents. Therefore their wastes and contaminated transport means can represent transmission factors in spreading of many diseases (e.g. foot-and-mouth disease). Rendering plants and sanitary slaughterhouses are of particular importance in this respect.

 

16.4 Influences of social factors

 

a) Social factors have indirect influence on epizootic processes and epizootiological situation. It is obvious that high standard of living, cultural level, stable political conditions and peace provide much better social environment for prevention and control of animal populations health and diseases and vice versa.

 

b) It is obvious that the hungry and poor people ("have-nots") need first to survive and animal disease control is usually out of their actual interest.

 

c) Similar importance have public and political support, animal health legislation, economic support through differentiated prices and subsidizes, standard of veterinary services, extension services, etc.

 

d) Animal health programmes and measures are directly targeted against animal population diseases (specific epizootic processes) to block, reduce, eliminate and eradicate them.

  

 


 

 

 

17. CONSEQUENCES OF ANIMAL POPULATION HEALTH AND DISEASES

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17.1 Introduction

 

a) Good health of animals is the main prerequisite for their effective production and optimal use and for human health protection against diseases transmissible from animals. Animal diseases have opposite impact.

 

b) Consequences can be of biological, economical, public health and social character.

 

c) Benefit of animal population health is much more important than the losses caused by animal morbidity and mortality. Unfortunately, majority of this kind of analyses is traditionally based on negative aspects. This debilitates our argumentation when looking for public, economic and political support for animal health programmes.

 

d) Analysis of animal health and disease consequences complements the analysis of epizootiological situation.

 

17.2 Characteristics of consequences

 

   Classification of consequences characteristics of animal health and disease has many criteria such as:

 

a) according to animal species and categories (e.g. losses in new born lambs)

 

b) according to causality (e.g. losses due to goat brucellosis)

 

c) according to environmental factors (e.g. losses due to bad ventilation causing respiratory infection in calves)

 

d) according to health/disease forms (e.g. losses due to nervous form of Newcastle disease in poultry)

 

e) according to quantitative aspects (e.g. benefit in milk yield of mastitis free cows)

 

f) according to qualitative aspects (e.g benefit in meat quality of cattle free of diseases - better prices and no restrictions in distribution and consumption)

 

g) according to direct/indirect impact (e.g. direct positive impact of health and negative of disease in natality, indirect positive/negative impact in body weight growing)

 

h) according to space (e.g. losses due to animal disease in ranch X.)

 

i) according to time (e.g. benefit of animal health during year 2007)

 

j) according to visibility (e.g. visible or observed losses due to dead animals, non-visible losses due to sanitary restriction of animal movement and trade)

 

k) according to measurability - ability to be quantified (e.g. measurable benefit in liters of milk, un-quantifiable benefits of protection of territory against introduction of exotic disease)

 

l) according to other criteria such as evaluation of total or of a part of benefit/losses,  relativity ,  etc. 

 

   Example: FAO  estimated in 1962 that average total losses caused by animal diseases in developed countries were about 15 percent and in developing about 35 percent; stamping out as benefit for the society but as loss for the farmer; what is loss for importing country can be benefit for exporting country.

 

17.3 Categories of health/disease consequences

 

17.3.1 Biological consequences

 

   Biological consequences reflect in changes of epizootiological situation (e.g. changes of number and proportion of healthy and diseased animals, disease free and affected herds), structure and characteristics of the biosphere (e.g. disappearance due a disease of an animal species having role in alimentary chain), density and structure of animal populations, etc.

 

   Example: Myxomatosis of rabbits introduced into Europe in the middle of 20th century from Australia to France devastated  domestic and wild rabbits in European continent during several months; wild rabbit population has not yet been recovered.

 

17.3.2 Economic consequences

 

   Positive economic consequences of animal health and negative of animal disease are multiform being reflected in:

 

a) Number of animals (total, per surface unit, per space volume unit, species proportions, category proportions, slaughtered animals rate, culled rate, culled rate due to diseases, natural mortality, etc.). Diseases determine critical limit for the concentration of animals in industrial type of production.

 

   Examples: Complete depopulation due to African swine fever mortality and sanitary slaughter in Dominican republic and Haiti in 1980-1982 reduced swine population from 1,5 million to zero.

 

b) Genetic value (proportion of genetically valuable animals, rate of high yielding animals, culled rate due to production reasons, etc.);

 

   Example: In Netherland in 1980 from total number of culled cattle only 30 % were due to biological (production) reason because 70 % must be slaughtered prematurely due to disease reasons.

 

c) Development (natality rate, survival-to-weaning rate, survival rate, breeding animals survival rate, fattening animals survival rate, age at weaning, age for feedlot, age of sexual maturity, age at first parturition, age for slaughter, new born weight, weight at weaning, weight at feedlot beginning, weight at a given age, weight at sexual maturity, weight at slaughter, weight gain per time unit, period for achieving a given weight, duration of active/productive life, etc.);

 

   Example: Aujeszky disease delayed feeding period in evaluated intensive type swine feedlots by about 20 days.

 

d) Reproduction performance (fertility, number of services per conception, duration of service period, reproduction interval,  number of new born animals per female in reproductive age during one reproduction cycle and during the whole life, replacement/restocking rate, etc.);

 

   Example: In Hungary, 1981, bovine tuberculosis caused sterility in 5 % of affected cows; bovine anaplasmosis in Argentina evaluated herds (1980) prolonged sex (conception) maturity by 81 days.

 

e) production performance (total production during a given period, during a production cycle, per day, per year; average production per animal during a given period, during a production cycle, per day, per year, per the whole life; production per time unit, per  space unit and per input unit such as feed unit, monetary unit, man power unit, etc.);

 

   Examples: In former Czechoslovakia in 1972  cattle affected by fascioliasis produced in average by 20 % less milk than healthy cows and lost 25 kg of body weight; according to FAO in 1980 following number of animals died in the whole world: 64 millions of cattle (12,7 millions MT), 128 millions of pigs (9 millions MT), 100 millions of sheep (1.5 millions MT) and 43 millions of goats (500 thousands MT).

 

f) quality of products (yield of slaughter animals - dressed carcass, grade of biological quality, grade of sanitary innocuity, grade of epizootiological innocuity, grade of utility - ability to be processed and used without restriction, price differences, etc.);

 

   Example: Prices of animal product from healthy herds are usually higher in comparison with diseased herds (if not prohibited to trade).

 

g) cost of veterinary measures (total, per animal, proportion from total cost of animal production, per year, per production unit, cost of animal health programmes, etc.);

 

   Example: Cost of successful programme of eradication of New World screwworm from North Africa in 1989-1991 cost 80 million US dollars; in former Czechoslovakia in 1971 state veterinary service budget was about 2 % of total value of domestic animals and their product.

 

h) economic impact of epizootiological restrictive measures on national and international trade;

 

   Example: During last three decades in the 20th century Southern American countries were prohibited to export beef to USA and Europe due to foot-and-mouth disease occurrence.

 

i) cost/benefit of animal production relating total input to total output in monetary terms (see chapter 34).

 

17.3.3 Public health and consequences

 

a) Positive public health consequences of zoonoses free health and negative of zoonotic diseases are multiform being reflected in: duration of human life, duration of productive life, grade of human health, grade of human welfare, grade of risk for human health, working ability, cost of drugs, vaccines, treatment, sanitation, etc..

 

b) While the effect of zoonoses on human production or output in terms of lost income and the cost of treatment can be quantified, the value of mortality and human suffering are completely different categories which cannot be evaluated in monetary terms.

 

   Examples: About fifty zoonoses can cause death in humans; vampire bat-transmitted rabies caused several hundreds deaths in Latin American countries.

 

17.4 Social consequences

 

   Positive social consequences of animal health and negative of animal diseases are multiform being reflected in: standard of living (income and consumption), cultural level and political activities.

 

   Example: Former Czechoslovakia in 1965 closed the border with Hungary to protect its territory against foot-and-mouth  diseases nearing wave which had political and social consequences (e.g. affecting more than one million of tourists, not speaking about interrupted trade).

 

17.5 Estimation of economic consequences             

 

17.5.1 Introduction

 

a) Analysis of economic consequences of animal population health and disease in based mainly on mutual comparison (differences) in quantity and quality between the productivity (utility) of all animals (real utility), of healthy animals (optimal/potential utility) and of diseased animals.

 

b) Analysis can include all aspects of economic consequences or only some of them (see above). It is recommendable to analyze first total and than partial consequences avoiding eventual double counting if the losses are caused by a complex of factors. It is important to keep in mind what the ceiling is on such losses.

 

   Example: Total economic losses due to foot-and-mouth disease in Southern America in 1970 were estimated to be of 378 millions US dollars; partial losses due to mortality and emergency slaughter were of 102 millions, trade restriction of 170 millions, etc..

 

c) Identification of disease is usually made on a clinical basis. Chronic debilitating diseases as parasitic infections, nutritional and fertility disorders, mastitis, and diseases of new born and young animals are caused by a wide variety of etiological agents. These complexes include etiological agents difficult or impossible to identify as the sole, or even the major cause of morbidity and mortality. It is precisely these chronic disorders that cause the greatest economic losses throughout the world.

 

d) Economic analysis is divided basically in calculation of benefit due to animal health and losses due to animal disease.

 

17.5.2 Principles for economic consequences calculation

 

a) The analysis processes concrete available data (direct calculation) or estimated data (indirect calculation). For both types clear cut definitions of measure units as well as of parameters and indicators to be used. Relative data must be combined with absolute data in order to be comparable with situation in other places and time. Therefore, any analysis must have also clear definition of space and time.

 

b) Direct losses can be calculated as the quantity of lost animals or their products multiplied by their prices. It is preferable to calculate first the loss in production measure units (easily comparable) and then to convert it in monetary terms (variable due to different money rates and inflation) as economic cost of disease.

 

c) Losses in animal products such as milk, eggs, etc. can be calculated as the multiple of the number of diseased animals by average loss (known or according to literature data).

 

d) Estimates of consequences in animal production can be calculated in following ways:

 

aa) Multiple of the difference between average production of healthy and diseased animals by the average number of healthy animals (benefit) or by the average number of diseased animals (loss).

 

bb) Multiple of the difference between the average production of total population and of diseased animals by the average total of animals (benefit).

 

cc) Multiple of the difference between the average production of healthy animals and of total population by the average total of animals (loss).

 

e) Estimates of consequences in input for animal production can be calculated in following ways:

 

aa) Multiple of the difference between average input for production of diseased and healthy animals by the average number of healthy animals (benefit) or by the average number of diseased animals (loss).

 

bb) Multiple of the difference between the average input for production of diseased animals and of total population by the average total of animals (benefit).

 

cc) Multiple of the difference between the average input for production of total population and of healthy animals by the average total of animals (loss).

 

 

 

 

 


 

 

18. INVESTIGATION OF EPIZOOTIOLOGICAL SITUATION

===============================================

 

18.1  Introduction

 

a) Investigation of epizootiological situation consists of activities to detect health/disease reality in animal populations and their environment. The epizootiological diagnosis is the objective and needed for epizootiological analysis and measures.

 

b) Prominent among the objectives are to detect the presence or to confirm the absence of disease-causing agents and factors.

 

c) There is significant difference between epizootiological and clinical investigations. In case of disease in one animal for the clinician is sufficient to investigate this animal taking into consideration influencing factors in very limited range to decide clinical (symptomatological) diagnosis. However, in the same case the epizootiologist must investigate all animals in the place, try to define etiological and epizootiological diagnosis (very often with the help of laboratory investigations) analysing many influencing factors inclusive in the neighbourhood and in the past, searching for the origin, sources and ways of introduction and propagation of respective etiological agents. However, investigation of individual animals is usually the basis for epizootiological investigation and diagnosis at population level.

 

d) The investigation has to find answers to the questions: "what, where, when,  how and why ?"

 

18.2  Principles of investigation

 

a)  The focus of the investigation is determined by the specific purpose to be achieved, i.e. the investigation should be target-oriented, sound and useful.

 

b)  The investigation process leading to epizootiological diagnosis detects and measures first the features (phenomena or symptoms) of animal population health and/or diseases and different factors acting upon them. Next the findings and their importance are evaluated and then the final diagnosis made.

 

c) Investigation should use exact and reliable diagnostic methods to identify the situation. These should give an undistorted, true picture of the reality. Therefore, highly specific and sensitive methods as required by the particular case should be used.

 

d) Investigation combines the qualitative and quantitative aspects of the epizootiological situation. The results are easier to compare and understand when the biological values of the diagnostic findings are also expressed numerically.

 

e) To achieve comparable results standardized - uniform diagnostic methods are required. This is particularly true for the identification od specific disease (etiological diagnosis) using indirect methods only.

 

f) Investigation, in line with its purpose and requirements, can cover the whole population (territory) or only a part over a sufficiently long period.

 

g) Investigation should lead to the swiftest possible epizootiological diagnosis, in accordance with the given objectives, particularly where the epizootiological situation is highly changeable.

 

h) Investigation utilizes different diagnostic methods. These vary in accordance with the object and specific purpose. More weight is given to decisive methods which look for the origin of specific disease(s). It is preferable to use a combination of available diagnostic methods.

 

i) Investigation should be flexible and adaptable to dynamic changes of the epizootiological situation.

 

j) Atypical or barely expressed symptoms and features deserve special attention as they are difficult to detect by the current diagnostic methods. Borderline areas between health and disease, negativity and positivity should receive similar attention.

 

k) In every case of new or suspected outbreak, one must first think about the worst, i.e. the most dangerous communicable diseases, and decide at the outset if such disease is involved or suspected. Only when the possibility of such a disease has been ruled out, beyond all suspicion, investigation moves on to detect what other cause might be involved.(See chapter 28).

 

l) Investigation for confirming disease free status of the populations, herds, flocks or groups requires well adjusted procedures which are not always the same as those for identifying the disease (where is often sufficient to isolate particular etiological agent in only one animal).For confirming disease-free status is necessary to investigate all animals or a representative sample using different methods.

 

m) Investigation methods should be feasible, relatively simple, technically realistic, rapid, easy-to-use and harmless. Unfortunately, very often the simpler and cheaper a method the less likely it is to produce specific, sensitive and exact results.

 

n) Vertical structure of diagnostic system has several steps between basic field level and highly specialized laboratories up to international reference centers for very specific investigations.

 

o) A network of diagnostic laboratories is often supplemented by mobile laboratories working in the field and processing fresh specimens.

 

18.3 Types of investigation

 

a) The types of investigation differ in accordance with their purpose, availability of biological and technical procedures, organizational conditions and economic resources.

 

b) How specific, complex and systematic the investigation is, as well as when and where it takes place, it depends on the analytical needs of the specific epizootiological situation. A detailed, broad-scope, in-depth investigation is needed to make a full and correct epizootiological diagnosis, covering the components and characteristics of both health and disease in a given animal population.

 

c) Different types of investigations are used separately or in combination in various situations in accordance with different purposes.

 

   It is preferable to use the surest and most important types, i.e. etiological investigation versus no-etiological investigation, complex versus partial, systematic versus operational, active versus passive, etc.

 

   It is preferable to combine various types as appropriate: general with specific, systematic with operational, local with territorial, one-time with long-term, related to preventive measures with those related to recovery measures, etc.

 

d) The basic requirement for a solid analysis of the epizootiological situation is an etiological diagnosis which reports on causes: disease agents and factors. Etiological investigations are oriented towards direct confirmation of the presence or absence of disease agents.

 

   Direct etiological investigation is based primarily on microbiological, parasitological, toxicological methods and biological tests.

 

   Indirect etiological investigation traces the presence or absence of disease agents through diagnostic methods focussing on specific impact (consequences) of these agents.

 

   Epizootiological and clinical investigations often lead to etiological diagnosis of the diseases with typical epizootiological characteristics and obvious typical clinical symptoms.

 

   Epizootiological and morphological investigations often produce an etiological diagnosis in diseases with typical epizootiological characteristics and typical morphological changes (postmortem investigation).

 

   Serological, allergic and biochemical investigations etc. often indirectly produce etiological diagnosis.

 

e) General (non specific) investigation covers animal populations, their products, environment, etc. from the general, no-specific etiological standpoint of animal health and disease, i.e. covering full etiological spectrum. The point in this case is to find out whether the object of the investigation is healthy or not.

 

f) Specific investigation covers the same above-mentioned objects from the standpoint of specific animal health and disease, i.e. from the standpoint of a single type of disease agent (mono-etiological investigation) or of a particular group (complex) of etiological agents and factors (poly-etiological investigations).

 

g) Systematic investigation is planned and oriented towards specific objectives in  contrast to occasional, non-systematic operational one. The first type is closely related to active investigations particularly connected with planned epizootiological measures.

 

h) Investigation differs in form, content, scope, place and time, selection of methods, etc. also in accordance with epizootiological measures preparation and monitoring the situation and results. They can be oriented to:

 

- active creation of animal population health

- preventive/protection measures

- epizootiological monitoring

- epizootiological surveillance

- disease-reducing measures

- disease-eliminating measures

- disease-eradicating measures, etc.

 

i) When the investigation does not cover all animals or other objects then it can be subdivided into representative one using sampling methods and non-representative one when sampling is not applied or the sample is too small. 

 

j) Investigation according to space  differs as to coverage which may be local, farm, ranch, village, municipal, regional, provincial, etc. Investigation can also be broken down by location: selected sites and ares (affected, threatened, disease-free, etc.), selected breeding/production units, by critical epizootiological sites (outbreaks, quarantine, markets, border stations, vectors areas, critical places of epizootic process, etc.)

 

k) Investigation according to time can be divided into: momentary, covering a period (short, medium, long), interrupted or continuous, one-time or repeated, regular (periodic, seasonal, cyclical) or irregular, etc. Key moments and periods of the epizootiological situation, development and measures always have the priority. Momentary investigation or in relatively very short period identifying the profile (cross cut) situation is often combined with longitudinal ones covering a longer period in the same animals (cohort).

 

18.4 Field survey and screening test

 

   Field survey and screening test represent diagnostic activities for defining general or specific epizootiological situation pinpointing its components (e.g. health, at risk and diseased animals, sources, disease-free zones, outbreak limits, etc.).

 

18.4.1 Field survey

 

a) Ad hoc survey is used to detect diseased or suspect animals, sources, ways of transmission, particularly in a new suspected or confirmed outbreak, to certificate disease-free animals, their products and neighbourhood zone for export and sale, etc.

 

b) Planned survey is used for analysing epizootiological situation as a basis for strategy, planning, executing, monitoring and evaluation of relevant measures, etc. This is highly demanding, expensive, laborious kind of investigation, as a rule, and for this reason is often done on representative samples.

 

c) Passive survey is that diagnostic activity which occurs accidentally in the normal course of veterinary work or cases where the veterinary service has been called in by stock-owner, etc. These are usually casual, isolated findings which help in a limited way to determine the occurrence or the absence (this is not reliable) of a specific disease in a given place.

 

d) Prevalence survey is used to determine the frequency and distribution of etiological agents by measuring the occurrence of antibody (produced to the agents) in the serum of the animal.

 

e) Longitudinal survey is that which lasts a longer period (years) investigating periodically selected health phenomenon in determined animals population, herd, flock or group.

 

18.4.2  Screening test

 

a) Screening test is the presumptive identification of unrecognized disease by application of simple tests to sort out apparently healthy animals which may have the disease from those that probably do not have the disease. Therefore, screening test (e.g. using serological, haematological, etc. methods) is applied to apparently healthy animals in search of disease with the objective of its early detection and therefore, early measures.

 

b)  Generally, screening tests are applied to a large number of animals and are often followed by other tests on those animals that are found to be positive. Most screening tests are aimed at high risk groups.

 

c) Screening is usually concerned with chronic diseases and aims to detect disease not yet under professional care. Mass screening means the screening of all population. Multiple or multiphasic screening involves the use of a variety of screening tests on the same occasion. Selective screening means the testing of certain group of animals.

 

18.5  Epizootiological investigation methods

 

a) Epizootiological investigation (diagnostic) methods consists of: observation of investigated objects (animals, animal products, terrain, sites, feeds, environmental factors, etc.), anamnesis, complex diagnostic methods carried out directly in the field (clinical, morphological, biological tests, etc.) and laboratories, available relevant documentation on the results of associated investigations in particular conducing to etiological and epizootiological diagnoses.

 

b) Epizootiological investigation usually selects the animals, animal products and other examination subjects as well as the kind, sites and time for taking and sending samples for laboratory examinations, and orient these investigations.

 

c) Epizootiological investigation methods interpret, combine, compare and relate to the actual field situation and, lastly, amalgamate (synthesize) all findings of all diagnostic methods used.

 

d) The main objective of epizootiological investigation is to make an epizootiological diagnosis by detecting and identifying the causes, occurrence, spatial and temporal frequencies, dynamic, trends and conditions of animal population health and disease.

 

e) Epizootiological investigation is primarily oriented towards the key components of collective health and epizootic  processes at critical (decisive) time and places. It is necessary to determine qualitative and quantitative properties of these components providing the basis for epizootiological indicators.

 

   The diagnostic systems and procedures differ according to epizootiological situation and its variability,  purpose, potential, degree of urgency (from preventive up to emergency investigations), etc.

 

f) Detected facts should be recorded. The finding should be noted down with care immediately (memory is always subject to lapses). 

 

g) Epizootiological methods are based on the fact that each process of specific collective health and each epizootic process has its specific epizootiological properties reflecting the specificity of the interacting population-etiological agents and the environment.

 

   Specificity is not reflected in clinical, morphological and physiological similarity alone, but also in epizootiological similarity (values of morbidity, lethality, focality, trends, ways of propagation, species susceptibility, etc.). Each epizootiological investigation method has limitations as to the scope of detecting disease in different situations.

 

h) Epizootiological investigation methods not only identify the situation, they also and primarily attempt to find the causes of a given situation and influencing factors for a correct orientation of subsequent measures - investigation for action!

 

i) Very important is to have an epizootiological hypothesis based on initial data. This is gradually confirmed, altered or substituted by a new or more likely hypothesis. "Blind" epizootiological investigation should be avoided. All investigations into concrete cases must be selective depending on the hypothesis and epizootiological logic (sense).

 

   Method of "gradual elimination" of different hypotheses is often used to find the most likely result.

 

j) It is essential that epizootiological investigation be carried out directly in the field, on specific sites.

 

k) Easily determinable and testable data and concrete finding are not always available, particularly on past events or in distant sites. For this such methods as estimations, associations, deductions, correlations, probability and hypotheses are also used.

 

l) For diseases common to both animals and man epizootiological investigation should be coordinated with epidemiological investigation of the human population.

 

m) It must be considered that laboratory investigation results can be obtained when field situation has already been changed in comparison with the moment of collecting the samples.

 

18.6  Diagnostic test quality

 

a)  Accuracy is the degree to which the measurement, or an estimate based on measurements, represents the true value of the attribute that is being measured. The accuracy of a test (proportion of those animals correctly identified by the test) can be measured and expressed by its ability to correctly classify the animals according to their health/disease status. These measures are termed sensitivity and specificity.

 

b) Sensitivity is the probability of a test to identify correctly those animals that are infected.

 

c) Specificity is the probability of a test to identify correctly those animals that are not infected.

 

d) True positive rate is the proportion of truly diseased animals that the test identifies as positive (predictive value of true positive results). A positive result can mean an infected, incubating, or recovering animal.

 

e) False positive rate is the proportion of the truly non-diseased animals that the test identifies as positive (predictive value of false positive results).

 

   A positive result does not necessarily mean that the animal has been recently infected with the etiological agents in question. A positive result may also indicate a prior vaccination to the agents or passive antibody transfer (i.e. through the colostrum). A test may also be positive due to laboratory or sample selection/handling errors. Occasionally, antibodies to another agent that has infected the animal will cross-reacts in tests used to determine exposure to another agent.

 

f) True negative rate is the proportion of truly non-diseased animals that the test identifies as negative (predictive value of true negative results).

 

g) False negative rate is the proportion of the truly diseased animals that the test identifies as negative (predictive value of false negative results). False negative animals are dangerous representing one of major transmitters of infectious diseases due to their transfer as healthy animals.

 

   A test may be negative when the animal is actually infected. An animal may have been recently enough infected at the time of the test that it has not had enough time to develop an antibody response (it takes usually two weeks before an IgM response is developed). In addition, a test may not be finely tuned enough to detect small quantities of antibody to etiological agents. A negative result could also be due to laboratory or sample selection/handling errors.

        

h) The sensitivity of a test is directly related to the amount of false positive and conversely, the specificity is related to the amount of false negatives. Specificity allows more confidence in a positive test. Sensitivity allows more confidence in a negative test.

 

i) Iceberg phenomenon is the portion of disease that remains unrecorded or undetected despite of diagnostic endeavours and population disease surveillance procedure called "submerged portion of iceberg". Detected or diagnosed disease is the "tip of iceberg". The submerged portion comprises disease not attended, attended but not accurately diagnosed and diagnosed but not reported.

 

j) Other important characteristic of diagnostic methods quality is repeatability or reproducibility (capacity of a measuring procedure to produce the same result on each occasion in a series of procedures conducted under identical conditions).

 

k) Diagnostic method general efficiency rate ("diagnosability") represent the multiple of test specificity and sensitivity.

 

18.7 Sampling in animal population investigation

 

a) Sampling theory is a study of relationships existing between a population and samples drawn from the population permitting to estimate certain characteristics of the whole population.

 

b) Sampling represent the basic tool in investigation of major animal populations facilitating to identify animal health and disease situation without testing all animals (which is extremely costly and demanding on manpower and other input resources and capacities).

 

b) Sampling uses the elements as the basic objects of interest (animals), sampling units (non-overlapping collections of elements which make up the population) and frame (list of sampling units in the population).

 

c) Probability sampling is a random access to every individual. Every individual in the population has a known chance of being sampled. Inference of the sample is applied to the rest of the population. The degree of bias depends on how the sample was taken and this will determine if the sample truly represents the rest of the population.

 

d) Non-probability (non-random) sampling is done on the basis of convenience or haphazard and the sample is usually not representative of the population under investigation. The problem with this type of sampling comes when the results are incorrectly applied to the entire population. This type of sampling may work and may actually be necessary at the beginning of an investigation because it may answer an initial questions about the situation.

 

e) Types of Probability Sampling

 

aa) Simple random sampling where every sampling unit has an equal chance of being selected in the sample. This type uses random number tables or software (assign each individual sampling unit a number).

 

bb) Simple stratified sampling where the population is divided into strata (subgroups) according to certain criteria that is important to the investigation. Then a random sample is performed among each strata.

 

cc) Proportional stratified sampling takes into account the problem of strata of unequal size. The sample among strata is obtained with regard to the contribution of the strata to the size of the total population.

 

dd) Cluster sampling where the unit of sampling is a group of individuals rather than a single individual. Every animal in sampled units must be surveyed.

 

ee) Multistage sampling is when more than one of the above methods is incorporated into the investigation design.

 

f) Sample size. The more units are sampled, the more accurate the results are. The more common the disease or characteristic are, the fewer is needed to sample. For the calculations of minimal number of sampling units in concrete cases relevant statistical methods to be used (see textbooks on statistics).

 

 

 

 

 


 

 

 

19. EPIZOOTIOLOGICAL INFORMATION SYSTEM

=======================================

 

19.1  Introduction

 

a) The purpose of epizootiological information system is to record, report, collate, process, store, transfer, diffuse and utilize data relevant to epizootiological situation. The system provides a basis for knowing the situation, understanding the various epizootiological phenomena and their frequency and dynamics and for decision-making on animal population health strategy and programmes/measures.

 

b) This system should transform raw epizootiological data into organized and meaningful information.

 

c) Information system components should form an integrated, functional unit designed to provide information needed for epizootiological analyses and actions, i.e. it should be tailored to concrete local requirements and conditions.

 

d) Standardized methods and definitions should be used. The data collected should be reliable, sound and above all useful (essential) in the light of the objectives.

 

e) Different epizootiological situation and requirements for decision-making need different data and adapted information system and sub-systems which should be flexible and dynamic with necessary grade of stability.

 

f) In every country exists a particular official information system linked with an international system and adapted to the local situation, needs and conditions.

 

19.2  Objectives of the information system

 

    The objectives are to supply essential data for:

 

- early warning and alarming system

- analysis of the epizootiological situation

- analysis of specific epizootic processes

- analysis of external factors influencing these processes

- guiding and facilitating future diagnostic activities

- epizootiological surveillance

- application of emergency measures

- epizootiological control of animals and their products movement

- issuing certificates and declaration of disease free status

- identifying epizootiological strategy, priorities and tactics

- application of effective epizootiological measures

- planning of animal population health programmes

- monitoring the progress and goals achievement of these              programmes

- evaluating the effectiveness of epizootiological actions

- early detection of constraints of programmes and measures

- effectively administrating, directing, controlling and              coordinating epizootiological activities, etc.

 

19.3  Information system data

 

a) Data for the information system should be above all:

 

- identified in advance in line with the purpose

- set out in a sound comprehensible standardized form

- reliable, sufficiently exact, official, specific and where possible numerical

- clearly defined in space and time

- primarily in absolute values as a basis for calculation of comparable indicators

- very carefully selected to record, report and process only a reasonable number of data.

 

b) The system has to cover the information on relevant characteristics of animal populations, etiological agents,  their sources and way of transmission, environmental (ecological factors), infectious processes, epizootic processes, economic and social factors, consequences of population health and disease as well as on different epizootiological activities (diagnostic, vaccinations etc.).

 

19.4  Data sources

 

a) The main data sources are the first-hand records of the veterinary services. There are different kinds of primary records such as card catalogues, cards, files, records books, statistical forms, etc. The data are kept and reported in the form of tables, maps, graphs, numerical, textual, photos, tapes, diskettes, etc.

 

b) Veterinary services registers are the most useful data sources. These are mainly first-hand records or protocols from:

 

- field veterinarians

- veterinarians in food industry

- border veterinarians

- veterinary clinics

- diagnostic laboratories

- production laboratories

- rendering plants

- veterinary services at all levels reporting notifiable diseases

- veterinary educational, scientific institutions, etc.

 

c) Non-veterinary services, agencies and organizations provide relevant data related to epizootiological situation:

 

- breeders and producers (state, cooperative, private)        

- breeders' organizations

- agencies monitoring wild fauna

- organizers of stock shows, fairs, markets and transport

- owners of processing plants for animal origin products

- insurance agencies

- services dealing with environmental aspects

- human epidemiological (public health) services

- meteorological services

- publications of national statistics and census agencies, etc.

 

19.5  Reporting

 

a) Reports on epizootiological data are to be standardized as to content, form, place and frequency to make data comparable and easier to process and assuring the uniformity.

 

b) Reports contents should correspond to the purpose and requirements respecting particular conditions and possibilities. Every data reported should have a specific importance and usefulness, i.e. it must be both necessary and useful.

 

c) Reporting priority have so called "notifiable diseases" which should be specified by national law or regulation including also the diseases according to international commitments (e.g. the diseases of the OIE list).

 

   Information on the occurrence or suspicion of notifiable diseases originate from:

 

- report on disease suspicion sent by the animal owners or other persons responsible according to the national legislation;

- findings made in routine veterinary work and inspection at the farm level;

- at official veterinary inspection particularly slaughter animals and meat inspection, import inspection, inspection of animal markets and other gatherings;

- notice received by compulsory notification;

- epizootiological preventive or control investigations.

 

  There should be appropriate and effectively enforced provision to ensure that every reasonably suspected case of a notifiable disease is reported by the general public to the official veterinary service, without delay. Effective measures should be applied to ensure that such obligation is complied with by veterinarians, livestock owners and attendants, butchers, knackers, and other persons which by profession, trade or regular occupation are directly concerned with animals or carcasses thereof. To that effect, it should be provided for that every case of serious disease or death in an animal, or alteration in a carcass, should be considered as being suspected of a notifiable disease, unless the symptoms can reasonably be attributed to another disease, which is not notifiable.

 

d) The forms of reports should correspond to their contents. Following informative tools - forms can be distinguished:

 

- telegrams, telex, fax, radio messages and courier services are used mainly in new cases of suspected or confirmed, highly dangerous, or exotic emergency diseases, or for as yet unknown disease of exceptional importance (spreading rapidly, causing high losses, etc.) in sites or areas previously free of such diseases, i.e. when the report must be sent immediately

- special printed forms (e.g. questionnaires for interview or mailed)

- cards containing first-hand data to be computer-processed

- protocols (standard form or free verbal text)

- text (letters) describing and commenting the situation

- epizootiological maps, tables, graphs (bar, line, scatter, area, pie, mixed, etc. types), photographs and recorder tapes

- telephone communications

- computer diskettes and tapes, CD-ROM

- computer modems, e-mail, on-line networks, etc.

 

  The most simple forms are the  interviews.

 

    Almost all the above-mentioned forms can be replaced in the future by on-line computer network linked with geographic information systems and eventually with satellite imagery.

 

e) The report channels go from field services through different management levels up to national veterinary headquarters. Data processed by the central organization is sent (feed-back) to inferior level reporting units and to relevant agencies and authorities.

 

f) According to epizootiological importance the reports to be sent

 

- immediately in new case of very dangerous disease and then continuously following its development (e.g. every day or in very short intervals)

- on regular basis in the case of notifiable diseases, on finding in slaughterhouses, laboratories, etc., on the progress of epizootiological actions, etc. (e.g. weekly, monthly, quarterly, six-monthly or annually)

- ad hoc in cases of particular interest, field surveys, diagnostic findings of major importance, etc.

- as compulsory - mainly on notifiable diseases as defined by national governments

- on voluntary or supplementary basis.

 

19.6  Data processing

 

a) At each level of organizational structure of veterinary services data of epizootiological importance are collected through the channels of communication (source-route-receivers) and processed.

 

     The data/reports are processed i.e. reviewed, summarized, interpreted and analyzed in different ways: by hand, machine, electrically or electronically.

 

     The data are arranged, grouped, classified and compiled in accordance with different purposes for which they were collected.

 

b) The information derived from the processed data is presented to users in appropriate forms for the specific purpose. Epizootiological bulletins or reports are published regularly at different intervals or irregularly in case of a danger of delay. These information is extremely important for all components of veterinary services providing them by the orientation necessary for their future diagnostic activities and epizootiological measures. Some information are addressed to public, first to animal owners.

 

c) Animal disease information archives are an important source to tap for retrospective epizootiological analyses of variations and long-term trends, comparisons and prognoses. The most advanced data source are disease data stored in the data banks of computers memory.

 

19.7  International systems

 

a) International epizootiological information systems based on the exchange of national data:

 

- are responsible for issuing warning on threatening dangerous diseases alerting close surveillance and preparatory measures for eventual emergencies

- assist with market analyses for decisions on whether to import animals or animal products

- assist in national and international control of the major diseases

- are responsible for international coordination including the preparation of international standards, definitions and codes assuring the uniformity and compatibility of all countries information systems.

 

b) By international agreements, animal disease reports are sent to veterinary services of neighbouring or cooperating countries and to multilateral, regional and world agencies such as International Office of Epizootics - OIE (Paris), Food and Agriculture Organization of the United Nations - FAO (Rome) and World Health Organization - WHO (Geneva). These international organizations publish bulletins, periodicals and yearbooks (e.g. actually OIE World Animal Health; FAO-OIE-WHO Animal Health Yearbook - up to 1996,) with data received from member countries.

 

           

 

 

 

                                     

 

 


 

 

20. ANALYSIS OF EPIZOOTIOLOGICAL SITUATION

==========================================

 

20.1 Introduction

 

a) Analysis of epizootiological situation (epizootiological analysis), based upon the interpretation and dialectic study of the results of epizootiological investigations, determines, evaluates and explains the characteristics and causes of  collective animal health and epizootic processes.

 

b) Analysis of available data  allows to deduce real epizootiological picture or that close to objective reality taking into consideration probability grade, epizootiological laws, scientific knowledge and previous experience.

 

c) Analysis initially seeks and studies  influencing factors which determine the origin, distribution, course, behaviour and extinction of respective health/disease processes in animal populations. Analysis helps to explain the differences in the health and disease status between different animal populations, herds and flocks and between different places and time.

 

d) Analysis facilitates the determination of the importance of different epizootiological phenomena as well as of the causal association between them. Knowing the natural or artificial causes, the hypothesis on the consequences can be formulated and checked. Knowing the consequences, the hypothesis on the causes and other determinants of the given epizootiological situation can be defined.

 

   Casual relations are the most important of the whole complex of interrelations between different components of the complex system - epizootiological situation and its development.

 

   Epizootiological analysis is supported by the hypotheses testing methods that investigate the association between given health or disease related events and possible causation factors.

 

e) Descriptive data obtained by the investigation of epizootiological situation serve as the source of epizootiological hypotheses which are to be proved using explicative analytical methods, and eventually experimental methods, followed by concluding synthesizing methods.

 

   The analysis should arrive at one or more hypotheses as to: the kind of epizootic process, the source of etiological agents, the possible mode of spread, etc. It should be checked that the hypothesis fits all the facts, i.e., that it is compatible with all observations; if it does not fit, the hypothesis should be revised.

 

f) The complexity, variability and dynamics of collective health process, epizootic process, influencing factors as well as different objectives and depth of the analysis call for a wide variation of analytic methods well adapted to the problem to be studied and evaluated.

 

g) Analysis procedure should be systematic and well programmed to include all important components and to be as most effective as possible.

 

h) Analysis should answer not only such questions as: what, where, in which species and category, when and how, but also why.

 

i) It is necessary to consider the fact that two same cases and two same epizootiological situations in absolute terms do not exist.

 

j) Generally, comparative methods are used which permit the evaluation of changes, differences and correlations between different phenomena, situations, places and time. The comparison of a specific case with those known in the past as well as accumulated experience and knowledge is of particular importance.

 

k) Analysis results help also to orientate subsequent investigation of epizootiological situation (selection of adequate places and time, animals to be investigated and sampled, types of specimens, types of investigation methods, diagnostic results interpretation, etc.).

 

l) Synthesis of the analysis results represents the basis for decision on epizootiological prognosis, strategy and measures as well as for their optimization, planning, execution, management, adjustment, control and evaluation.

 

20.2 Principles of epizootiological analysis

 

a) For each specific analysis the objectives, objects, space and time should be defined in order to obtain valid conclusions with respect to the problems under study and the measures to be taken.

 

b) Well defined objectives ensure the correct orientation of analytical procedures toward the phenomena which are decisive for the solution of specific animal population health/disease problems.

 

c) Each analysis should have well defined and delimitated objects giving priority to those of major animal health importance. There is a need for defining which animal species and categories, etiological agents/factors, specific health and/or disease, epizootic process, forms and stages, space and time, etc. should be the major objects.

 

d) All analyses should study and evaluate each phenomenon from the point of view of space and time which are closely interrelated and in which the movement, changes and development are reflected. The space analysis determines the space dimension and relations with other places (e.g. neighbourhood). The time analysis determines the duration and relations with the past, present and future.

 

e) The phenomena should be analyzed not only from the point of view of absolute values but also of relative values.

 

f) Analysis should study and evaluate the phenomena not only from the qualitative (characteristics) but also quantitative (dimension) points of view. Quantitative changes reaching critical values lead to qualitative changes.

 

g) Analysis of animal population health phenomena should study and evaluate not only their forms but also their contents (substance) which are mutually interrelated and interdependent.

 

h) It is desirable that the analysis is based on a "system approach", i.e. the particular components to be analyzed as integral parts of a system. The phenomena should be analyzed as an integral component of the whole complex system (epizootiological situation). Individual components form a particular structure of the system and are mutually interrelated. In analysing a disease situation individual affected animals should always be considered as integral components of a complex - affected herd, flock or population.

 

i) Animal health phenomena should be analyzed dynamically, i.e. from the point of view of absolute changes, movement and development with relative stability.

 

20.3 Type of epizootiological analysis

 

a) Types (methods, contents, form, range) of epizootiological analysis vary according to different aspects such as objectives, objects, specificity, space, time, complexity, etc. Each analysis and its procedure should be well adjusted to its purpose, conditions and feasibility respecting importance grade of the given problem.

 

b) According to the objectives, following analyses can be distinguished: preparative analysis, preventive analysis (related to animal health protection), recovery analysis (related to recovery, elimination and eradication measures), surveillance analysis, evaluating analysis (related to the effect of measures), certifying analysis (related to veterinary certificates), scientific analysis (related to experimental works), etc.

 

c) According to the objects, following analyses can be distinguished: analysis of all animal populations, of the populations of a group of species, of the population of one species; of all the categories (perfil analysis), of one group (cohort analysis); of a healthy population, of a diseased population; of a suspected population, of population at risk, etc.; of etiological agents, of their sources and ways of transmission; of the environmental factors; of collective health process; of epizootic process; of influencing factors; of individual cases (case study); etc.

 

d) According to etiological aspects, following analyses can be distinguished: etiological analysis (from the point of view of determined etiological agents) or non-etiological analysis which does not respect the causes but only the external manifest forms and consequences.

 

e) According to the specificity, following analyses can be distinguished: general analysis (non specific - including all etiological agents/factors aspects); specific monocausal analysis (according to one species of etiological agents); polycausal analysis (according to a particular group of etiological agents species and etiological factors).

 

f) According to space aspect, following analyses can be distinguished: local analysis (of a herd, flock, farm, etc.), geographical - territorial analysis (of a lowland area, desert area, island, etc.); political - territorial analysis (district, regional, provincial, national, etc.); sectorial analysis (of private, cooperative, state sectors, etc.); rural zone analysis, urban zone analysis; analysis of disease free zone; analysis of intrafocal area; analysis of perifocal area, etc.

 

g) According to time aspects, following analyses can be distinguished: analysis at a given moment (transversal), of a period (longitudinal); retrospective analysis (of the past - historical - ex-post); actual situation analysis; continuous analysis; periodic analysis (regular - daily, weekly, monthly, yearly, seasonal, cyclical, etc.); no periodic analysis (irregular - operational; ad hoc; case study, etc.).

 

h) According to the complexity aspects, following analyses can be distinguished: complex analysis including all the phenomena of a given situation and using all available data; incomplete analysis dealing only with a part of the components of a given situation; deep analysis evaluating the details; superficial analysis evaluating only orientation factors.

 

i) According to the other aspects, following analyses can be distinguished: analysis of the herds according to their size, concentration, specialization, technology, etc.; analysis using different forms such as network analysis, "critical path" analysis, etc.

 

20.4 Evaluation of epizootiological phenomena

 

a) In analysing animal population health situation there should be always the effort to evaluate it in the most objective and precise form as possible. This requires first that the given phenomena (variable) are well defined and delimitated and where possible, in a standard and measured form using respective numerically expressed measurement units. Mathematical expression facilitates the application of statistical methods needed for evaluation of mass phenomena and the use of relative indicators (rates, ratios, indexes). Statistics is the tool by which data are reduced to manageable form and tested for significance.

 

b) Generally, the analysis is supported by a great number of different data and information which can be properly utilized only when using statistical, in particular bio-statistical methods. In this connection the analysis utilizes the indicators in the form of respective symbols and formulae.

 

20.4.1 Standardization and measurement

 

a) The fundamental condition for good analysis is its uniformity, i.e. standardization of the definition of the phenomena and used indicators. The definitions are usually based upon experimental results or so called "normal values" - averages obtained by evaluating a great number of data. If international or national standards are available then they should be used.

 

b) In order to be able to use statistical methods, there is a need to define the given epizootiological phenomena units as statistical units.

 

c) The data used can be: quantitative - expressed numerically and able to be measured; qualitative -  indicating only if the given variable is present or absent, eventually quality grading (in proportions); continuous which also includes values between whole numbers (integers); discrete which include only the values expressed in whole numbers.

 

d) Different scales are used for analysing data: ordinal scales, interval scales (with changeable or fixed initiation, with regular or logarithmic intervals), graduation scales (parallel or cumulative).

 

e) Following units of measurement are used: biological (animal, disease case, herd, outbreak, etc.); measure units of length, surface, volume, mass, time, velocity (length by time unit), density (quantity by space unit), etc.

 

20.4.2 Frequency distribution of animal health phenomena

 

a) The distribution of animal health phenomena varies greatly. Frequency distribution of absolute quantitative values are often grouped in different intervals, classes or categories so that they can be better processed. Frequency distributions of qualitative values are based on the proportion (percentage) of a given variable within a given complex (population sample) of statistical units. Another type is represented by cumulative frequency distributions.

 

b) Frequency distributions can be symmetrical or bell-shaped (Gauss curve) or asymmetrical which is the case in the majority of epizootiological phenomena. The distribution can be modal, bimodal, binomial, etc.

 

c) The expressions such as "usual, habitual, current, regular, normal, etc." are not sufficiently determinant and comparable. This is the reason why more precise definitions are preferred using statistical methods when and where possible. These methods facilitate the synthesis of frequency distributions using a few values of statistical parameters of their central tendency and their dispersion.

 

   The averages and measures of the central tendency represent the center of frequency distribution. For this purpose arithmetic mean, median, mode, geometric mean, etc. are used.

 

   In order to characterize properly a complex (population or sample) of quantitative values it is necessary to know also dispersion or variation around the central value. For this purpose range (dimension) of variation, average deviation, variance, standard deviation, coefficient of variation, etc. are used.

 

d) Evaluating frequency distribution curve following statistical criteria are used: confidence intervals, confidence limits, confidence level, confidence coefficient, etc. By convention 95%-99% confidence limits are usually chosen.

 

e) The results obtained by statistical processing of available data should be tested for statistical significance - level of significance (acceptable maximum of probability to risk an error). In animal population health analysis, 0.05 (5 %) and 0.01 (1 %) levels of statistical significance are usually used.

 

f) In the ensemble of phenomena which are defined through two or more different quantitative values there is the need to study relations - dependency between those variables using regression and correlation methods. Each acceptable association between animal population health variables calculated as statistically significant should have clear epizootiological (biological) sense.

 

g) The tests of the difference between two or more means and two or more proportions are very often used.

 

h) For the estimation of unknown values interpolation methods have proved to be useful.

 

   Note: More information see in statistics textbooks.

 

20.4.3 Space aspects

 

a) Each animal population health phenomenon is related to a given space (place) and therefore also its location, density (concentration) and space dispersion (regular, irregular, in cluster, etc.) should be evaluated.

 

b) Space location and delimitation are expressed in terms of natural, political - administrative, economic and other limits. In vast territories geographical coordinates are used for this purpose.

 

c) Space size or dimension is expressed in surface units, eventually in volume units (in case of aquatic phenomena).

 

d) For evaluation of phenomena density the relation of the number of units to the space size is used.

 

e) Each analysis should give priority to the places of major epizootiological importance, i.e. those which are decisive for the given situation and for respective measures (critical places).

 

f) The maps (spot, transparent overlay, etc.), area charts or cartograms with epizootiological phenomena location represent fundamental documents for space analysis.

 

20.4.4 Time aspects

 

a) Each animal population health phenomenon is related to a given time and therefore its time delimitation should always be evaluated giving the priority to those moments and periods which are of major importance for the given situation and measures (critical moments/periods).

 

b) Chronological distribution evaluation is based on the study of time series (stable, evolutive or periodical, such as seasonality, cyclical variation, etc.). Current and chain indexes are used for comparative studies of time series.

 

c) It must be always considered that all phenomena change and develop during time. In animal populations, herds and flocks the replacement of old by new generations is of particular importance as diseased, vaccinated, investigated, etc. animals are gradually replaced by healthy, non vaccinated, non investigated animals, etc.

 

d) The beginning and end as well as duration of each phenomenon should be evaluated using calendar units or relative units such as "animal/days", "animal/years" or "outbreak/days", etc. The average duration as well as periods with and periods without a given phenomenon (diseased animals, specific foci, etc.) are also important time criteria.

 

20.4.5 Indicators for epizootiological analysis

 

a) Epizootiological analysis uses not only simple absolute data, parameters, determining the frequency and magnitude of the phenomena as the result of respective investigations and measurements, but also relative data in the form of indicators (rates, ratios, indexes). When presenting relative data respective absolute data should be always mentioned.

 

b) Rates or proportions express the relation of phenomenon frequency as a part of a total of respective statistical measurement units. The values are presented in the form of simple proportions, of %, %o or by every 10000 or 100000 measurement units.

 

c) It is always to take into consideration the relativity of the indicator values. The same absolute value gives different values in relation to different size of population (e.g. 100 affected animals signify only 1 % within a population of 10000 animals while within a population of 1000 animals this represents 10 %).

 

d) It is always desirable to mention investigation grade, i.e. the proportion of investigated animals or herds multiplied by the value of general efficiency rates of the given investigation methods.

 

20.4.6 Prevalence, incidence and extinction

 

a) Each epizootiological phenomenon has its beginning, duration and end. In relation to a given period it can:

 

- begin and terminate within the same period

- begin in and continue after this period

- exist before the beginning of the period and terminate within the period

- exist before and continue after the period.

 

  This four possibilities form the basis for differentiation of prevalence, incidence and extinction rates.

 

b) The phenomena which exist at a given moment are projected in point prevalence rate, those which exist during the period are projected in period prevalence rate and the average of these phenomena existing during the period is projected in average prevalence rate.

 

   Point prevalence facilitates the evaluation of the perfil ("transversal cut") of a given situation at a given moment without providing information on the dynamics of the situation. It is often used for evaluating the phenomena of longer duration, e.g. in chronic diseases. The period prevalence and average prevalence include all the phenomena existing during a given period without taking into account their beginning and end.

 

c) The new phenomena in a given period are projected in incidence rate. This rate must respect time factors, i.e. in relation to the number of animals existing in a given period or in average or at a given moment (e.g. initial).

 

   The incidence expresses the changes (new units) during a given period and therefore it is very important indicator for evaluating epizootiological dynamics and grade of stability or  instability having major use in acute diseases.

 

d) The extinct phenomena in a given period are projected in extinction rate. This rate must respect time factors, i.e. in relation to the number of animals existing in a given period or in average or at a given moment (e.g. initial).

 

   The extinction (negative incidence) also expresses changes during a given period due to disappearance of a given phenomenon (e.g. elimination, recovery, transfer, slaughter, etc. of diseased animals) and has major use in monitoring and evaluating the measures aimed to achieve animal health recovery (reduction, elimination or eradication of animal diseases, etc.).

 

e) Prevalence rates are based on the number of existing, incidence rate on the new and extinction rate on disappeared phenomena during a given period in a given place.

 

  (Attention: Prevalence, incidence and proportion of positive tests are often confused !).

 

   See indicators formulae in annex.

 

20.5  Animal population disease dynamics

 

   For  evaluation  of  animal disease dynamics  following criteria or indicators can be used:

 

- chronological time series of disease frequencies;

comparative  indexes  (current  and  chain) correlating  given values with the initial or previous ones;

average  of  changing  numbers   of  diseased animals during individual sub-periods of a total evaluated period;

seasonality of  animal  diseases as monthly proportions in the total year value;

‑ surviving rates of diseased animals based on multiplication of surviving probability rates in individual sub-periods;

birth rate as ratio of new born per female of reproductive age;

‑ changing number of diseased animals in reproduction cycle;

‑ changing number of diseased animals in production cycle;

tendency  indicators  of  animal  disease based on the balance between new and extinct cases during a given period in relation  to their number at the beginning;

cyclic  tendency  disease development based  on  the difference between the minimum and maximum numbers of diseased animals and duration between two peaks of the curve;

‑ ascending tendency disease development based  on the difference between  the  initial  minimum  and final  maximum  number  of diseased  animals  and duration  of  period  for  reaching the maximum;

‑ descending tendency disease development based on the difference between  the  initial  maximum  and final  minimum  number  of  diseased  animals  and duration  of  period  for  reaching the minimum;

diseased  animals territorial movement criteria including direction,  velocity (distance per time measure unit), distance  (in length measure units) and duration (in time measure units); etc.

      

20.6 Analysis of animal population health status

 

a) The purpose of the analysis of animal population health status is to determine its epizootiological characteristics using the whole analysis systems of population collective health and morbidity/mortality parameters and indicators respecting animal population basic characteristics.

 

b) Epizootiological risk is the probability that an event will occur, e.g. that animals will become diseased or die within a given period of time or age. The qualitative or quantitative estimation of the likelihood of adverse effects that may result from exposure to specific health hazard or from the absence of beneficial influences is to be evaluated. Epizootiological risk is usually assessed using such indicators as relative risk grade, odds ratio, attributable risk grade, proportion of attributable risk, etc.(See Annex).

 

c) Analysis of general and specific resistance against disease is of particular importance. Following indicators can be used: immunized animals rate (vaccination coverage of population) which could be combined with herd coverage or territory coverage by vaccination; relation vaccinations/animals; vaccination repetition rate. The immuno-effectiveness of vaccine used should be always taken into consideration.

 

d) In analysing population collective health situation and process, the objects, such as etiological aspects, contents, forms etc. of a given collective health must be well defined. Healthy animals rate (proportion of healthy animals in the whole herd or population) represents the basic indicator for this purpose. Animal population viability analysis uses the indicators such as population viability index, natality and fertility and survival rates.(See chapter 5 and Annex).

 

   To be able to declare and maintain the herd and/or population or territory as specific disease free, particular analysis is required to prove epizootiological wholesomeness.

 

e) In analysing animal population morbidity the diseased animals rate is used as a basic indicator. The group of mortality rate indicators (proportion of dead animals) can be subdivided into the group of natural and artificial mortality. In specific disease the indicators of lethality (proportion of dead diseased animals) reflect the severity of the disease. (See chapter 6 and Annex).

 

f) Epizootiological structure of a given animal population is a very important component of the analysis. The basic structure is represented by the population composition and proportions of diseased, indeterminate and healthy animals (exposed and not exposed, resistant and susceptible, investigated and not investigated, etc.). (See chapter 7).

 

20.7 Analysis of other components of epizootiological situation

                                                     

a) Etiological analysis is aimed first at confirming the presence or absence of etiological agents (factors) in a given population or in a given place (territory). If their presence is confirmed then the analysis studies their properties of epizootiological importance, sources and ways of transmission. (See chapters 8,9 and 10).

 

b) Environment factors analysis evaluates their impact on epizootiological situation and its development using specific criteria and measurement units for the assessment of atmospheric, geospheric, hydrospheric and biospheric influencing factors. (See chapter 11).

 

c) In analysing specific infection process main attention is given to its origin, course, stage, duration and forms including its severity (see chapter 12). Animals - carriers without clinical symptoms are of particular importance.

 

d) Analysis of the epizootic process is based on the study and evaluation of the interaction among the animal populations, etiological agents and environment (epizootic triad).

 

   In specific epizootic processes the analysis is aimed at the study and evaluation of the epizootiological chain of the circulation of etiological agents (more complex in polyhostal processes), course and stages, forms, range and intensity, grade (exceptional, sporadic, enzootic, epizootic, panzootic), etc. Diseased animals rate in the form of attack rate is used in acute disease outbreaks. Further aspects of analysis are: epizootic process localization, territorial delimitation, distribution, movement and development, time delimitation, duration, etc. (See chapter 13).

 

e) In the case of zoonoses the analysis of epizootic and epidemic processes in animal and human populations requires very close cooperation between animal and public health services. The above-mentioned principles for epizootiological analysis are similar to those used for epidemiological analysis. (See chapter 15).

 

f) Territorial analysis includes the study and evaluation of the foci (outbreaks) and epizootiological regions (zones).

 

aa) The foci characteristics of major importance to be analyzed are: focus etiology, focus host spectrum, form, size, manifestation grade, activity, localization, time delimitation, stages, etc. The natural foci study is also oriented towards the circulation of etiological agents in nature, biotic structure, vectors and reservoirs activity, etc. The perifocal situation should always be evaluated together with intrafocal analysis.

 

bb) Nidality (focality) grade is measured using indicators such as nidality (focality) rate, affected herds rate, etc. (See chapter 14).

 

cc) Epizootiological regionalization structure is based on determination of disease-free zones, affected zones and threatened zones. For the measurement of these zone the indicators of the epizootiological zone rates can be used.

 

20.8 Analysis of economic and social factors

 

a) It is preferable to combine epizootiological analysis with the analysis of economic and social factors influencing animal population health and measures. Among the most important factors belong: rural development and in particular economic activities in livestock husbandry, local economic level, urbanization, industrialization, transport, trade, tourism, etc. Living standard, cultural level, political conditions and other social factors cannot be underestimated. (See chapter 16).

 

b) This analysis also includes the study and evaluation of biological, economic, public health and social consequences of population health (benefit) and mass diseases (losses). (See chapter 17).

 

c) Epizootiological measures should be always taken into account. In order to evaluate the extent of these measures following indicators can be used: treated animals rate, treated diseased animals rate, territorial coverage by measures, population coverage by measures, herds coverage by measures, period coverage by measures, etc.

 

20.9 Forms of analysis presentation

 

   The forms used for the presentation of the results of epizootiological analysis are similar to those described in chapter 19 dealing with information system.

 


 

 

21. EPIZOOTIOLOGICAL MONITORING AND SURVEILLANCE

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21.1 Introduction

 

a) Epizootiological situation and its development as well as the influencing factors are subjects of monitoring and surveillance in order to obtain and maintain the knowledge about the situation and to apply corresponding actions in time.

 

b) Epizootiological monitoring and surveillance represent particular systems based on investigation, information and analysis activities described in chapters 18, 19 and 20. Both types are interrelated.

 

21.2 Epizootiological monitoring

 

a) Monitoring means to collect, process and use of ad hoc information and investigation results obtained during the current veterinary services activities to assess the specific health and diseases status.

 

b) Monitoring consists in operative investigations to decide immediately about epizootiological measures, usually at local level or to prepare further steps for the analysis and eventual animal health programme.

 

c) Monitoring involves regular (routine) or irregular veterinary inspections in the field and slaughterhouses, laboratory investigations, veterinary control in the disease foci, in quarantines, etc.

 

d) Monitoring not always is followed by concrete actions if the disease is not of actual importance or has not necessary priority in epizootiological strategy.

 

e) Initial monitoring represents the first phase of epizootiological activities before starting active screening and animal health programmes. It consists in obtaining the first information on specific disease occurrence in the territory if the disease exists or not and in positive case what is its approximate distribution and consequences.  Initial monitoring has different forms where the first investigations and ad hoc findings are complemented by the first active "sondes" to achieve better knowledge about the "new" problem.

 

f) In the majority of known diseases initial monitoring represents  still the only specific activity due to the fact that there are not yet the conditions for starting complex and effective programmes for their reduction, elimination and eradication.

 

g) Follow-up monitoring means the observation over a period of a group, or initially defined population whose appropriate characteristics have been assessed to observe changes in health status or health-related variables.

 

21.3 Epizootiological surveillance

 

21.3.1 Principles

 

a) Epizootiological surveillance is a continuous process of  observing, investigating, analysing, evaluating and examining carefully and constantly all development and pertinent alterations of the epizootiological situation and factors influencing it. The purpose is to predict and detect in time (i.e. at the onset) dangerous epizootic threatening to worsen a given situation, to determine the state of epizootiological emergency, and to immediately alert the services and organizations involved.

 

b) Surveillance particularly attempts to predict and detect, measure and evaluate changes or trends for the worse in the behaviour of problem diseases, detect and assess unexpected risks and determine critical moments and places.

 

c) Surveillance mainly scrutinizes quantitative changes for worse of selected phenomena which have reached a critical point, producing a qualitative change for the worse, i.e. deteriorating of epizootiological situation.

 

   In essence, it is a scrutinizing of certain events that is used to detect a change in animal health/disease trend or distribution to modify investigative or control measures and to identify promptly any emerging disease syndromes which would require immediate response from a veterinary or a public health services.

 

d) Surveillance makes possible timely preparation, application and eventual modification of epizootiological strategy, programmes and measures. Surveillance provides the fundamental basis for epizootiological prognoses and continuous upgrading of specific activities for a swift appropriate reaction to changes in the animal population health situation.

 

e) Surveillance provides information required to meet international reporting need and to  support declarations  of disease  status for trading purposes particularly if exotic diseases involved.

 

f) Surveillance can be:

 

-  general, covering the full etiological spectrum

-  specific, covering particular etiological aspects, i.e. specific animal health or disease processes.

 

   As a rule, epizootiological surveillance focuses on a limited number of carefully selected diseases such as the exotic ones, the most dangerous ones and those under intensive reduction, elimination or eradication programme, i.e. diseases having a major economic and public health impact.

 

g) Calling attention for the new situation and threatening risks (particularly the appearance, suspicion and possible outbreak of an exotic disease) represents a major step forward in prediction and prevention.

 

h) Early warning system is a specific procedure to detect as early as possible any worsening departure from usual or normally observed frequency of dangerous animal health/disease phenomena. The warning system for health hazards for people,  animals, environment can include also chemical contaminants.

 

i) Surveillance is a continuous process which depends on scientific developments and field experience. On the other hand, it influences the theory and practice through new finding and results as well as its demand for new methods and supply of new ideas.

 

21.3.2 Objects of epizootiological surveillance      

 

a) The objects of surveillance are all phenomena connected with collective health and epizootic processes, as well as factors influencing these processes. Of priority interest are alarming manifestations, potentially or actually prejudicial to the future development of the epizootiological situation which can lead to the spread of existing diseases or to the origin (introduction) of new ones.

 

b) Surveillance of animal populations mainly applied to changes in numbers and structure by species and categories, in animal productivity, movements, trade, etc. Surveillance focuses on changes which tend to increase the degree of exposure (risk) to selected specific diseases and to decrease population resistance (immunity levels) against these diseases.

 

   Among the main objects of surveillance are healthy populations, herds and flocks at epizootic risk, recently recovered (risk of recurrence), affected and suspected, forms of disease, morbidity and mortality trends, etc.

 

c) Etiological agents  and their characteristics of selected infectious diseases and of newly detected are studied evaluating changes and appearance of new types, subtypes and strains, undesirable major changes of pathogenity, antigen structure, immunogenity, tenacity, drug resistance, etc.

 

d) Transmission factors of etiological agents are also scrutinized, in particular the movement and import of domestic and wild animals and their products, human population long distance migration as well as behaviour of vectors of selected diseases of natural nidality. Factors which could lead to the introduction of a new dangerous exotic disease have top priority. The surveillance of all aspects facilitating the long-range spread of disease heading to eventual panzootic is of particular importance.

 

e) Surveillance objects involve also influencing environmental factors such as atmospheric, hydrospheric, geospheric, biospheric and nutritional ones of which some major changes could worsen the epizootiological situation. Their impact can be in lowering animal population resistance, promoting overpopulation and the spread of etiological agents vectors and reservoirs and contributing to transmission mechanism.

 

f) Surveillance studies and evaluates changes in epizootic processes  which may lead to a worsening of the epizootiological situation. This mainly involves changes in: stages of epizootic processes (e.g. post-epizootic into inter-epizootic, pre-epizootic into ascending stages, etc.), forms (from mild to severe), grades (an enzootic threatening to become an epizootic, an epizootic to become a panzootic), range of distribution (risk to be spread in disease-free areas), etc.

 

g) Once a disease has been eradicated, the recovered population (zone) is "watched" for a long period until it is quite sure that specific etiological have been completely exterminated (risk of recurrence).

 

h) Where selected diseases can be transmitted from animals to man, data and findings of human epidemiological surveillance are also used.

 

i) Economic and social factors having potentially a major negative impact on epizootic processes are objects of surveillance as well.

 

j) Deficiencies and gaps in epizootiological measures against selected diseases belong among surveillance objects similarly as in diagnostic efficiency and capability, extension activity and specific research. In this context the availability, use and side effect of vaccines, insecticides, drugs and other substances used are continuously studied.

 

k) The biological, economic, public health and social consequences of selected diseases are studied and evaluated to detect and predict worsening undesirable adverse effects.

 

21.3.3 Epizootiological surveillance methods

 

a) Full spectrum of epizootiological investigation, data gathering and processing, analysis and monitoring (inspection) methods can be used for epizootiological surveillance. (See chapters 18,19 and 20).

 

b) The methods should be carefully selected and tailored to the purpose of surveillance, to the special nature of selected diseases (specific epizootic processes) and to particular situation at a given time and in a given place.

 

c) In addition to examining and evaluating available data on the results of investigations, analysis and monitoring, data from related branches such as public health, livestock husbandry, processing industry,  trade, etc. are also studied and evaluated. Data which may indicate a possible worsening impact on epizootiological situation receive a particular scrutiny.

 

d) Data on international disease situation, particularly in neighbouring and exporting countries are carefully examined and evaluated.

 

e) Data published in the literature on new scientific discoveries and field experience pertinent to selected diseases and unofficial information on their occurrence are also examined and evaluated.

 

f) Available data are sometimes supplemented by: field surveys, additional experiments, comparative studies of microbial strains and serums of different provenance and dates (microbes and serum banks), etc. Among important studies belong the comparison between field strains and specific vaccine production strain to confirm if they are compatible or not.

 

g) To study and evaluate the risk of penetration or survival of specific disease agents, highly susceptible and healthy animals so called "sentinel animals" free of specific agents, are sometimes placed in sites which are suspect or at risk. The purpose is to detect in time the eventual existence and/or frequency of these agents as they are "caught" by the sentinel animals. These animals are controlled and investigated in an attempt to isolate the suspect agents and/or detect sera conversion in animal's blood (appearance or increase of specific antibodies).

 

h) Surveillance can be passive, i.e. rely on legal or voluntary  reporting or active in which aggressive efforts are made to collect information from all available sources.

 

21.3.4 Organization of epizootiological surveillance

 

a) The vertical and horizontal organizational structure of the veterinary services provides the basis for epizootiological surveillance organization including almost all components of these services.

 

b) Surveillance is organized at all levels, from field to national and international levels.

 

c) For processing and evaluating surveillance data, use is often made of specialized reference centres at national and international levels which have specialists in respective diseases.

 

d) The results (findings) of epizootiological surveillance are distributed in time to agencies and officers participating in and responsible for selected animal population health programmes.

 

e) Epizootiological surveillance is multidisciplinary by nature and for this reason requires very close cooperation among animal health specialists (epizootiologists) and experts in other related fields (epidemiologists, microbiologists, parasitologists, immunologists, ecologists, entomologists, biostatisticians, etc.).

 

f) Good coordination between epidemiological and epizootiological surveillance is essential for diseases common to humans and animals. In fact, a joint surveillance programme is the best.


 

 

 

22. EPIZOOTIOLOGICAL THEORY, EXPERIMENTS AND STUDIES

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22.1 Introduction

 

a) Epizootiology, similarly as other biological sciences, has its constant development based not only on the analysis of natural events and practical experiences but also on theoretical and experimental works.

 

b) Field or laboratory practice is the best testing place for the confirmation that the conclusions of the theory and experiments are correct and useful.

 

22.2  Theoretical methods in epizootiology

 

22.2.1 Development of epizootiological theory

 

a) Epizootiological theory consists in a complex of reasoning which explain and make intelligible the epizootiological phenomena.(Theoretical epizootiology).

 

b) The development of this theory is based mainly on generalization of discoveries produced by scientific activities such as experiments under field, laboratory or simulation conditions, practical (empiric) experiences and field observations. From these results new laws, principles, standards, norms, classification, definitions and methods are deduced and formulated.

 

c) The development of epizootiological theory is based also on the application of some laws, principles and methods of other related  medical, natural and technical and philosophical sciences.

 

d) Majority of epizootiological phenomena has mass character where probability theory permit to study their features using exact mathematical methods.

 

22.2.2 Epizootiological hypothesis

 

a) Epizootiological hypothesis represents the idea with the expectation that it will conduce to the explication of epizootiological phenomena (historical, actual, future) or to the discovery on new facts, relations, causes or consequences, using accumulated knowledge and experiences as well as epizootiological logic.

 

b) Formulating the hypothesis methods of difference, concordance, analogy, causal association (cause - effect / consequences), etc. are used.

 

   Causal association. A "cause" is a thing or event which when changed itself makes something else also change. "X causes Y" if a change imposed directly on X results in a change in Y.

 

c) The null hypothesis states that the result observed in a study, experiment, or test are no different from what might have occurred as a result of the operation of chance alone.

 

d) Each hypothesis is to be confirmed or refused. In the latter case it should be replaced by a new one. The confirmation can be based on natural observation or the experiment. Generally, for the comparison the sets of experimental and control units are used or past and actual phenomena values (comparative retrospective study). Principles of sampling must always be respected (see chapter 18).

 

e) The quality (probability) of the hypothesis expressed in numerical values (statistical hypothesis) should be tested by statistical methods indicating also the grade of error.

 

22.2.3 Epizootiological prognosis

 

a) Epizootiological prognosis is the prediction of the future development of particular phenomenon based on available past and actual data on it, on its past tendency as well as on accumulated knowledge and experience.

 

b) Prognosis is very important for  epizootiological strategy, programmes and measures. It requires good knowledge of respective processes and influencing factors.

 

c) The tendency can be determined in form of graph projecting the past time series data in a line or curve extending it into the future (prospective line or curve). It is obvious that in case of a disease with the periodicity (seasonality or cyclicity) the curve must be adequately adjusted.

 

d) If no major changes are expected the tendency can continue in the same trend. If major changes are expected then the tendency will be changed according to the changes of phenomenon determinants (e.g. increase of resistance due to mass vaccination).

 

22.2.4 Epizootiological modelling

 

a) Modelling of epizootiological phenomena using abstractions of the reality through language of symbols (verbal, physical, schematic or mathematical) facilitates to understand epizootic processes as well as to forecast the future development.            

 

b) Mathematical/statistical models explain different aspects of the occurrence of a variety of diseases. With some infectious diseases, models have been generated to elucidate the reason for epizootic and/or to predict the behaviour of the disease in reaction to given control measures. It is a representation of a system, process or relationship in mathematical form in which equations are used to simulate the behaviour of the system or process under study.

 

c) Simulation is a model system, e.g. a mathematical model or an animal model, to approximate the action of a real system, often used to study the properties of a real system.

 

d) The models should be logical, flexible and based on professional knowledge and experience. The field or laboratory practice tests the reliability of the model results.

 

22.3 Experimental methods in epizootiology

 

22.3.1 General principles

 

a) Epizootiological experiments (experimental epizootiology) consist in artificially inducing a characteristic which changes natural course of animal population health/disease or influencing factors in order to discover, confirm or demonstrate determined epizootiological phenomena, their causes, functions and consequences. These experiments represent the strictest tests of causal relations in epizootiology.

 

b) Generally, in epizootiological experiment a population is selected for a planned trial of a regimen whose effects are measured by comparing the outcome of the regimen in the experimental group with the outcome of another regimen in a control group. To avoid bias members of the experimental and control groups should be comparable except in the regimen that if offered them. Allocation of individuals to experimental or control groups is ideally by randomization (randomized controlled trial).

     

22.3.2 Types of epizootiological experiments

 

a) Epizootiological experiments have different objectives, contents and forms. The basic  form is the comparison between the tested and compared "control" animals (or other sets of units). The comparison can be simultaneous (with paired or standard units) or successive (with past units - historically). Both types can be carried out between different groups treated differently or between identical groups treated differently.

 

b) Epizootiological experiments are different in field conditions (field trials) where  virulent etiological agents cannot be used and in laboratory with much better conditions for work with dangerous agents and for more precise selection, monitoring and evaluation of experiments. Laboratory and field experiments are usually interlinked.

 

c) Relatively often, before introducing new epizootiological methods, vaccines or drugs in practice, pilot tests are used (after confirming the effectivity and harmlessness first under laboratory conditions and following tests are applied in a small groups of animals under field conditions to confirmed the results).

 

d) Intervention trial is a planned experiment designed to assess the efficacy of a treatment in animals/herds by comparing the outcome observed under the test treatment with that observed in a comparable group of animals/herds receiving a control treatment. ( The term "treatment" is used as a broad definition of any possible intervention such as treatment for a particular disease or diseases, vaccination programs, and management/environmental maneuvering).

 

e) Experimental studies strives to make the treatment groups as similar as possible (e.g., breed, age, sex, nutrition, housing) with the only "difference" between the groups being the treatment given.  By "controlling" everything the outcomes can be compared (usually using simple statistics) with relative assurance that any difference seen was in fact due to the treatment.

 

f) Bioassay consists in quantitative evaluation of the potency of a substance by assessing its effects on tissues, cells, live experimental animals, etc. Bioassay may be a direct method of estimating relative potency: groups of subjects are assigned to each of two (or more) preparations; the dose that is just sufficient to produce a specified response is measured, and the estimate is the ratio of the mean doses for the two (or more) groups. In this method the death of the subject may be used as the "response". The indirect method (more commonly used) requires study of the relationship between the magnitude of a dose and the magnitude of a quantitative response produced by it (dose-response assessment).

 

22.3.3 Evaluation of epizootiological experiments

 

a) Generally, the results of the experiments are evaluated using statistical methods. The purpose is to confirm or reject epizootiological hypothesis, define central values and the dispersions, associated values, correlation and regression values, difference between experimental and control units, test of statistical significance (probability) and its level.

 

b) The smaller the probability (P) value, the less likely it is that the observed relative difference is just due to random variation. P-values generally need to be smaller than 0.1 or 0.05 to be considered significant. (Not all statistically significant associations are causal.)

 

c) Among statistical tests often used in epizootiology belong: Student 't' test, F test, chi-square test (contingency tables), etc.

 

d) Interpretation of the results must have epizootiological sense (logic), i.e. must be biologically meaningful.

 

22.4 Epizootiological studies

 

a) Different observational study designs may be used to test hypotheses about causes of disease.  A common component of all observational study designs is the comparison of two or more groups. Studies may be broadly classified as prospective or retrospective depending on whether the outcome of interest has already occurred.

 

  Observational studies are used the most in epizootiological studies. This kind of studies allows nature to take its course without intervention in the disease process. Studies may be done with relationship to time, factor exposure or disease status.

 

  In these studies, called also analytic studies, individuals  may be classified according to absence or presence (or future development) of specific disease and according to "attributes" that may influence disease occurrence. Attributes may include age, race, sex, other disease(s), genetic, biochemical and physiological characteristics, economic status, various aspects of environment, etc.

 

b) A chief advantage of observational studies is that they are directed towards the species of concern in its natural environment. This greatly reduces the problems associated with extrapolation of results from a particular study to the target population. It also allows to test a much broader range of hypotheses than would be possible under controlled experimental conditions.

 

c) A major disadvantage of observational studies is the possibility of biases especially confounding which may distort the true relationships between variables. Missing data are also a common problem in prospective studies because animals are sold, die or lose their identification.

 

d) Types of observational studies

 

aa) Cross-sectional study (syn.: disease frequency survey, prevalence study) where the sampling is without regard to exposure or disease status. The prevalence of the disease in question are measured and compared among those with and without the suspected risk factor(s) of interest. Evidence for a causal associations is only realistically produced for permanent factors such as breed and sex.

 

bb) Case-control study where the sampling is on the basis of disease status. The animals, litters, herds, or some other units with the disease of interest as the "cases" and units without the disease as "controls" are selected. Information about prior exposure history to "risk factors" is gathered and compared among the groups. These studies are well suited to rare diseases and many risk factors can be evaluated at the same time. They are quick and easy to perform but subject to many potential biases.

 

cc) Cohort study (follow-up study) where the sampling is on the basis of exposure status. Representative animals (or litters, herds, etc.) exposed to a selected risk factor are selected along with a comparison group which is not exposed to the factor. The natural course of events is merely observed. After a suitable period (longitudinal study) the incidence of disease of interest is compared between the groups.

 

    The groups or populations, selected on the basis of whether they have been exposed to risk, received a specified preventive or therapeutic procedure, or possess a certain characteristic, are followed to assess the outcome of exposure, the procedure, or effect of the characteristic, e.g. occurrence of disease.

 

dd) If all the relevant events (exposure, disease, etc.) have taken place prior to the study then the study is retrospective, otherwise the study is prospective. Cohort and case-control studies can be both prospective and retrospective.

 

ee) Ecological study in which the data are collected on the basis of a group rather than for each animal individually. This kind of study is done when more than one factor needs to be studied in their relationship to the disease.

 

e) Blind(ed) study (Syn.:masked study) in which is intended to keep participants in a study from knowing some facts or observations that may bias or influence their actions or decisions regarding the study. These studies can be single-blind, double-blind or triple-blind trials.

 

22.5 Bias

 

a) Bias is the distortion of results by neglected factors, e.g. due to systematic error in the data. It is not a matter of random variation or imprecision. Bias is caused by messed-up study designs.

 

b) Selection bias is a systematic error in the way that the samples of subjects were drawn from their underlying populations, or in the way that subjects were assigned to interventions (or other maneuvers).

 

c) Information bias is a systematic error in the way that data were gathered or measured. All data potentially are subject to imprecision (random variation). There may be a systematic error (inaccuracy) in the measuring tool compared to the best possible tool. There are also systematic errors that are applied differentially between groups.

 

d) Diagnostic  bias consists in errors when using non-standard (non-uniform) methods and tools (objective errors), when different investigators using the same methods  obtain different results in the same animals or samples (subjective errors) and when methods with poor sensitivity and specificity are used.

 

e) There are other types of bias such as:

 

- confounding epizootiological indicators (e.g. prevalence, incidence and proportion of positive results)

- making conclusions without taking into consideration the dynamics of population health/disease processes

- not respecting space and time aspects

- making conclusions not respecting the possibility of false negative and false positive results, of possible influence of previous vaccination or treatments

- making premature conclusions based on incomplete analysis

- lack of critical evaluation of the results                

- lack of epizootiological logic when interpreting the results, etc.

 

 

   Note: More information on statistical methods see in respective textbooks).

 

 


 

 

 

23. EPIZOOTIOLOGICAL STRATEGY AND MEASURES

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23.1  Epizootiological strategy

 

23.1.1 Introduction

 

a)  The strategy for disease prevention, control and eradication (further "strategy") represents the policy which, respecting society needs, biological and methodological as well as economic and organizational feasibilities, identifies main concepts, priorities and objectives and determines systems - principal methods for achieving these objectives in a most effective way.

 

b)  The strategy, programmes and practical measures should be based on an adequate analysis of epizootiological situation as well as on prognosis considering influencing factors.

 

c)  The decisions are made at different levels of organization management structure. Usually, the strategic decisions are carried out at international and national level (political - strategical). The decisions about the concrete field measures are made at the lower - local levels (operational - tactical).

 

d)  The priority intention is to maintain and strengthen benefit factors of population health and reduce till eliminate damaging factors of diseases.

 

e)  Protection of human health represents the priority objective of society. One of the component of public health strategy is the protection of man against diseases transmissible from animals.

 

f)  Before a specific strategy is decided, the level of knowledge about the causes of the disease, its sources and transmission ways, host range and the nature of the host/parasite relationship as well as diagnostic feasibility should be considered.

 

23.1.2  Society needs - strategy basis

 

a) Strategy for disease prevention, control and eradication represents an integral component of the overall social and economic development strategy. The needs of human society are to be fully respected and its requirements met effectively as a contribution to social and economic development of the country.

 

b)  The strategy should first create as effectively as possible the animal health conditions, particularly for the improvement of the production of food of animal origin in its quality and quantity and the contribution to the protection of human health against zoonoses and food-borne diseases.

 

c)  The strategy should contribute to desirable and uninterrupted development of animal breeding, production and reproduction with minimum possible inputs.

 

d)  Some difficulties are linked with interests and priorities differences between  particular social groups, between society and individuals, between state and private sectors, between producers and consumers, between national and local levels, etc.

 

23.1.3  Strategy concept

 

a)  Strategies for animal disease prevention, control and eradication apply  general social and economic development strategies in the field of animal health and protection of human health.

 

b) The strategy is based on the  epizootiological, epidemiological, economical, social and political analyses and on the tendency studies and prognosis.

 

c)  The strategy reflects general veterinary philosophy prevailing in the given country. Preventive medicine concept is prevailing in some countries, while the curative concept is prevailing in the others.

 

d)  Only healthy animals create conditions for effective breeding and production and for the protection of human health against the diseases transmissible from animals. Therefore, the preventive concept is more effective and cheaper with  better impact on production improvement than curative treatment of sick animals ("fire brigade" concept).

 

e)  The problem is not to achieve the objectives at any costs but to achieve them in a most effective way.

 

f)  Preference should be given to the strategy and application of those concepts  and methods which have already proved in practice to be feasible and effective under comparative conditions.

 

g)  The positive results of the strategy and its implementation programmes should be consolidated and maintained, i.e. to convert them in lasting effect.

 

h)  The strategy should be flexible in case of significant changes in epizootiological situations and/or in influencing factors to be able to adjust the programme and keep it functional.

 

23.1.4  Strategy priorities

 

a)  In all the countries, there are so many animal health problems that in none of them the solution of all problems is realistic in the next future. Therefore, there is an imperative need to identify the most urgent problems which solution is feasible under the given conditions.

 

b)  Identification of the priorities helps the concentration of the available forces and resources on the main problems solution which promises successful and beneficial results.

 

c)  The strategy priority represents the cross-result of the complex analysis and identification of biological, economic, public health and social priorities after being corrected by the degree of feasibility and expected benefits.

 

d)  The procedure can start with preparing a list of epizootiological problems in the order of importance and urgency. Problems which solution is still unrealistic will be eliminated from the list. Among the high priority problems should be included the most important ones considering the specific diseases situation and grade of feasibility and expected effectivity of the programmes.

 

   One of the methods which has proved to be useful consists in following procedure: First step is to prepare a list of diseases to be  considered and then they  should  be  evaluated by  their  biological, economic, public health and social importance grades (e.g., scale from 0 to 10).  The  obtained  values  to  be  multiplied  by importance coefficients  for  different  forms  of  importance.  The results (numbers  of points)  is corrected (multiplied)  by solution feasibility and inputs  availability grades (e.g.  scale could be also from 0  to 10). The order of priority is given by the number of points obtained.

 

e)  Those diseases which are in final phase before their eradication, although the losses caused by them are not more the major problem, should be included among the priorities.

 

f)  Particular attention is given to those diseases which are officially notifiable due to their importance. The situation of these diseases is usually better known than of the others giving more reliable basis for the analysis and prognosis.

 

23.1.5  Strategy objectives

 

a)  Every strategy should have its objectives to be achieved. The clear cut objectives facilitate to maintain the orientation "line" and to concentrate on programmes and activities aiming at the final goal. The objectives expressing the situation which should be by the end of the given period represent the basis for planning of particular measures.

 

b)  The objectives should define  what, where, when and what level or quality should be achieved. Measurable parameters have the preference. The objective should be demanding and mobilizing but feasible.

 

c)  Examples of objectives to be achieved:

 

- specific disease-free territory created, protected or extended;

- specifically healthy herds, farms or population created, protected or extended;

- proportion of specifically healthy animals detained or increased to a given level;

- fertility, natality or/and weaning rate increased to a given level;

- general or specific morbidity detained or reduced to a given level;

- specific disease(s) eliminated or eradicated;

- specific disease(s) focality detained or reduced to a given level or eliminated;

- specific epizootic process detained, reduced to a given level, slowed down to a given level, interrupted or eliminated, etc.;

- general or specific disease mortality / lethality or other losses detained, reduced to a given level or eliminated; etc..

 

d)  In the case of healthy animals, diseased animals and focality rates the use of point prevalence rate is preferable.

e)  The objectives of the strategy and implementing programmes can also be expressed in public health terms (specific human health protected, improved, specific zoonoses morbidity decreased or eliminated, zoonoses mortality eliminated, etc.), economic terms (e.g. particular productivity maintained, increased, improved), ecological terms (e.g. healthy environment created, protected, expanded, recovered),etc.

 

f)  Global strategy aims at gradual eradication of specific diseases of major importance in the whole world.

 

g)  The strategy and implementing programmes should have not only temporary but sustainable effect which requires often demanding follow-up activities.   

 

23.1.6  Strategy types

 

a)  The strategy can be general covering animal health and diseases in full etiological spectrum or specific dealing with specific health and diseases only.

 

b)  The strategy can cover all animal species in a given country or territory or only one or few selected animal species.

 

c)  The strategy can be a complex one covering all aspects of the given problem or partial, dealing only with specific aspects of the given problem.

 

d)  The strategy can be oriented to particular objectives such as:

 

- active creation of animal population health;

- prevention (protection) of animal population health;

- increased rate of healthy animals;

- simple control of epizootiological situation;

- reduction of animal morbidity;

- elimination of specific disease (point prevalence = 0);

- eradication of specific disease (incidence = 0);

- reduction of animal mortality;

- protection of human population health;

- reduction of human population zoonoses incidence;

- elimination of human population zoonoses incidence; etc.

 

e)  In zoonoses particular importance has the common epizootiological and epidemiological strategy protecting, expanding and recovering human population health through improved specific animal population health.

 

f)  The strategy can cover (determine) also the activities such as:

 

- diagnostic activities;

- prophylactic activities;

- sanitation activities;

- mass treatment activities;

- epizootiological surveillance; etc.

 

g)  According to the space aspects the strategy can be territorial covering whole countries or zones or particular sectors, production branches, etc.

 

h)  According to the time aspects the strategy can be temporal, short-term, middle-term, long-term or perspective.

 

i)  In some diseases doing nothing  can be applied when

 

-  the morbidity may be absent or reduced by natural changes in host/parasite relationship without the intervention of man (e.g. due to the lack of natural vectors, inadequate climate, absence of susceptible species, etc.);

-  the low importance or lack of necessary conditions for desirable actions do not require  or permit any control programme for the moment.

 

     Today, unfortunately the majority of the many hundreds of transmissible and non-transmissible diseases (mainly chronic and subclinical) are still waiting for specific actions which have been postponed for the future after solving the diseases of major importance with the chance for successful programmes.

 

23.2  Factors influencing epizootiological strategy

 

23.2.1  Introduction

 

a)  To select an optimal strategy it is necessary to analyze, respect and eventually exploit the influencing factors such as biological, ecological, economic, social, political, organizational, etc. These factors, on the one hand, orient and create conditions for practical programmes and measures and on the other hand limit their feasibility.

 

b)  When deciding on the strategy, the biological, public health, economic and social influences and consequences of the animal health and disease must be taken into consideration.

 

c)  The diversity of the specific epizootiological situation and complexity of many influencing factors require concrete decisions to be taken in any particular situation.

 

d)  Comparison of expected effectiveness of a given strategy with the expected (supposed) situation development when no adequate actions are taken, is of particular importance.

 

23.2.2    Biological and ecological factors

 

a)  The biological factors and aspects have the primary importance for the decision on disease prevention, control and eradication strategy. In particular, the epizootiological situation as well as biological and methodological feasibility must be considered. Unfortunately the effective and reliable biological methods for achievement of desirable strategy objectives are not always available.

 

b)  Among  biological and ecological strategy influencing factors belong the following ones:

 

aa) animal population general characteristics: (number of animals, population structure according species and categories; animal productivity and behaviour; physiological and genetic development; animal reproduction; population location, density and concentration in farms, herds or flocks; population horizontal and vertical movement; nutrition status; etc.); (see chapter 2);

 

bb) animal population epizootiological characteristics:

general and specific susceptibility and resistance grades; values of animal population health (general and specific) grade and viability; animal population morbidity and mortality (general and specific); animal population epizootiological structure (healthy, diseased, suspected, threatened, exposed, etc.).; (see chapters 3-7);

 

cc) etiological agents and their characteristics of epizootiological importance (such as pathogenity, tenacity, transmissibility, life cycle, etc.); sources of etiological agents and ways of their transmission; (see chapters 8-10);

 

dd) environmental factors and their characteristics: atmospheric, geospheric, hydrospheric, biospheric, nutritional, etc.; (see chapter 11);

 

ee) infectious diseases that affect or can be transmitted by only one species of host are relatively easier to control and eradicate that the diseases with a wide host range; diseases due to exogenous agents can be identified and controlled easier than diseases due to endogenous and ubiquitous agents (their overall eradication is impracticable).(See chapter 12).

 

ff) epizootic processes characteristics such as specificity, contents, susceptible species, development stages, forms, range, intensity and grade, location, distribution and propagation, time delimitation, duration, frequency, variability, etc.; (see chapter 13);

 

gg) nidality characteristics; diseases with natural nidality involving wild animals and/or with arthropod vectors are particularly difficult to control and eradicate; (see chapter 14);

 

hh) etiological agents transmissibility to man and zoonoses epidemic process characteristics such as specificity, development stages, forms, morbidity, location, distribution, time delimitation, frequency, etc.; (see chapter 15).

 

c)  Effective specific prevention, control and eradication are possible only if a particular disease can be recognized and the main epizootiological characteristics are known.

 

d)  The possible ecological consequence of a given strategy as well as  the desirable ecological balance in a given ecosystem should always be considered, particularly in diseases with natural nidality.

 

23.2.3  Economic factors

 

a)  Economic factors usually play a supporting, stimulating or limiting role when the strategy is to be decided.

 

       Among these factors belong such as economic situation of the country or territory, of the breeders, producers, consumers, of veterinary services, etc. There is the problem of economic feasibility of the strategy.  Necessary economic resources are not always available.

 

b)  Among the economic factors are those as general economic level, grade of urbanization and industrialization, transport and communication, trade, etc. Rural development, livestock breeding and production development (organization, structure, concentration, specialization, technology, management, etc.) should also be considered. (See chapter 16).

 

c)  Availability of necessary inputs such as financial funds, transport, fuel, energy, investments, facilities for diagnostic and production laboratories, veterinary drugs, equipment, instruments, etc. are indispensable for animal health strategy and programmes. This availability depends on the priority grade within the state and private sector budgets.

 

d)  Losses compensation, prices' differences, livestock insurance complement economic factors complex, as well as financial contribution of the enterprises, cooperatives and private sector to the animal health programmes. Governments usually cover the cost and consequences of obligatory measures of society interest such as mass investigations and vaccinations, final sanitation in foci of dangerous diseases, losses due to emergency slaughter, etc.

 

e)  Some animal health programmes temporally limit economic activities, reduce breeders and producers income (limitation or prohibition of animal movement; limitation of animal products use and sales or their confiscation, etc.). Drastic measures consequences require adequate economic compensation.

 

f)  The importance, role and position of animal production in general economic development as well as in the export or/and import of animals and their products should be always taken into account.

 

g)  If the strategy and programmes are to be successful, necessary economic resources must be available or the strategy and programmes must be adjusted to limited resources.

 

h)  If a control or eradication campaign involves the slaughter of many animals, sufficient replacement stock should be available in livestock industry to minimize the disruption of the breeding and production.

 

23.2.4   Social factors

 

a)  Social factors influence the strategy and programmes supporting, stimulating or limiting them. The main social factors are standard of living, culture standard, political conditions as well as conditions of peace and war.

 

b)  In the countries and territories with very low living standard where the poor hungry people have the priority in surviving, the desirable interest in animal disease control strategy is usually lacking.

 

c)  In the countries and territories with low percentage of alphabets and low culture standard, the strategy is much more difficult to apply than in the countries and territories with opposite characteristics.

 

d)  The strategy can also be supported or limited by traditions, habits and religious prejudices.

 

e)  Availability and adequate standard of mass communication (extension) means for informing, explaining, convincing and mobilizing the farmers and other inhabitants, are of extraordinary importance.

 

f)  The selected strategy is easier to apply where political system is stable, where laws and government authorities are respected, where the local power and political organizations actively support animal health programmes.

 

g)  Social differences in interest in the strategy and programmes such as between the society and individual and group interests, national and local interests, should always be taken into consideration.

 

h)  Support of the selected strategy depends a lot of  conviction grade of concrete programmes feasibility. Examples of successful results under similar conditions are the best arguments. Uncertainty about results is one of the most difficult obstacles. Veterinary service itself should be convinced first.

 

i)  Usually the strategy and implementing programmes are easier to apply in state sector than in private sector where economic profit aspects are decisive.

 

j)  Views of veterinarians, public health specialists, breeders, producers and society must be always considered. Their opinion and the degree of their cooperation are influenced by their understanding of the strategy and implementing measures.

 

k)  Suitable legislation with provision for compensation is indispensable.

 

l)  Effective strategy and implementing programmes can be carried out only under peace conditions.

 

23.2.5   Organization factors

 

a)  Every veterinary strategy requires adequate organization of animal health services in terms of its standard, capacity, activity, structure, diagnostic facilities, manpower (standard, number, distribution), funds, transport, etc. at all levels from field up to national.

 

b)  The strategy and implementing zoonoses programme requires also adequate organization of public health services.

 

c)  Organization of animal husbandry, food processing as well as political and administrative system and structures must be respected.

 

d)  Animal health services cooperation and coordination with public health services and other participating services and organizations is essential for any successful strategy and programmes aimed at animal disease prevention, control and eradication.

 

e)  Strategy based on obligatory measures supported by government infrastructure and legislation is easier to apply than the campaign on voluntary basis requiring adequate incentives.

 

23.3  Epizootiological measures

 

a) Epizootiological measures represent practical activities for the implementation of the strategy and programmes aimed to reach respective objectives.

 

b) Measures should be well targeted to their purposes and goals using the most convenient and effective methods. Due to the fact that every case is different, the selection of adequate measures in concrete cases based on previous analysis is decisive. Routine and "mechanical" application should be avoided. Applied measures should be indispensable, reasonable, logical, feasible and well justified and defensible.

 

c) Where possible planned and complex measures are preferable to ad hoc and isolated measures (e.g. in first moments of a new disease outbreak when applying provisional measures). 

 

d) Preference is given to the primary measures against the cause of animal disease, i.e. against specific etiological agents, their sources and ways of transmission to interrupt epizootiological chain and thus protect healthy animals. These measures are decisive, however, they are usually complemented by a series of supporting secondary measures.

 

e) Measures should be defined in a very concrete form. Everybody responsible for particular measures application should know what, how, how much/many, where, when and why they should be carried out. The measures should be fully understandable which is the preconditions for the discipline in their applications.

 

f) Majority of effective preventive and control measures consists in prohibiting, limiting, restricting or regulating respective activities of animal owners, breeders, producers, public etc. Therefore, the measures are to some extent conflicting and "complicate" the normal life and production.

  

g) The methods to be used should be based on previous practical experience where they proved to be feasible and effective under the given field conditions. New methods should be first applied in limited number of animals in a form of pilot test.

 

   For current daily field epizootiological work so called "experiments" should be avoided. Any fiasco causes general mistrust in the professionals' competence and in the given programme feasibility which is very difficult to overcome in the future.

 

h) Measures can be obligatory or voluntary depending on local legislative and government decisions. For major programme at population levels to be effective obligatory measures are a must.

 

i) The grade of measures exigency depends on many factors. It is increasing following increasing epizootiological importance of animal population, place and time moments or periods, increasing pathogenity, contagiousness, speed of propagation of etiological agents, morbidity, nidality, losses, etc. and vice versa. It is decreasing following increasing of the distance of foci and sources of etiological agents, resistance, chronicity, etc. and vice versa.

 

j) Particular attention is given to critical groups of animals, places, moments and periods influencing specific epizootic process in decisive way.

 

k) Measures should be relatively stable during the necessary period but also flexible to be able to adjust to changed situations.

 

l) Only the measures which are implemented consistently can assure expected results.

 


 

 

 

24. ACTIVE CREATION OF ANIMAL POPULATION HEALTH

===============================================

 

 

24.1 Introduction

 

a) Active creation of animal population health consists in the formation of new generations composed of healthy animals.

 

b) Active creation of animal population health has different forms:

 

- through the use of only healthy animals for reproduction purpose

- through the replacement of old generation by healthy new born animals

- through the formation of new farms, ranches and breeding areas using healthy animals only

- through the formation of new herds composed by healthy animals only in farms, ranches and areas previously depopulated.

 

c) The most natural creation of animal population health is the exploitation of current or accelerated replacement of old generations by the new ones usually born as healthy or in better health. This offers the opportunity for gradual improvement of epizootiological situation.

 

d) The selection of healthy animals for future breeding and production can be from general or specific diseases point of view. Other aim of active selection is to reinforce general or specific resistance against diseases.

 

e) Active creation of collective health should be linked with the formation of healthy environment, areas and territories, i.e. free of particular etiological agents. Other epizootiological measures such as prevention, control and eradication contribute to the same objectives.

 

f) Collective health once achieved should be consolidated and protected.

 

24.2 Creation of new healthy generation of animals

 

24.2.1 Selection of healthy  animals for reproduction

 

a) Careful selection of only healthy females and males for reproduction purposes is decisive step for the formation of a new healthy generation. Therefore genetic and reproduction policy should be directed (programmed) toward the selection of the most convenient animals with the best health.

 

b) Selection of the new reproductive males for an elevated number of females is of particular importance. Selection criteria have to be not only from the production and reproduction points of view but also from the animal health aspects (free of infectious and hereditary diseases, resistance against diseases, etc.). Selection should be based not only on anamnesis and clinical investigations but also on specific investigations confirming etiological agents free status.

 

c) Only healthy parents are able to produce healthy new born animals, i.e. new healthy generation.

 

24.2.2 Replacement of old generation by healthy new born

       animals

 

a) Almost in all cases the animals are born without etiological agents. This is the chance to keep them healthy protecting them against these agents.

 

b) Reproduction cycle provides the conditions for transmission of many communicable diseases from one generation to the new one, from elder populations to younger ones.  Therefore,  the vertical isolation between old and young animals is effective method to avoid  vertical transmission of communicable  diseases. 

 

c) Breeding of new  born healthy animals separately from old animals which  are often not in  good health, is the chance  to  improve  gradually  population  health  due to step‑wise replacement of old generations by new  ones with better health.

 

d) Semi-artificial breeding of new born animals consists in immediate isolation of these animals from their parents and other animals, in an environment  free of pathogens. The colostrum should be from healthy animals or special substitute to be used. These animals should be kept isolated in the same groups avoiding contacts with other animals and fed with etiological agents free feedstuffs.

 

e) Premature weaning is also a form of semi-artificial breeding when making shorter the period of direct contacts between the new born animals and their mothers through the colostrum.

 

f) Specific-pathogen free (SPF) programme is the most advanced form of artificial breeding.

 

aa) It consists in new born mammalian animals through hysterectomy of healthy mother under sterile conditions and their immediate isolation in a space free of pathogens. The isolation can last up to their weaning or longer or up to the end of their life.

 

    Example: SPF technology and  schemes of SPF swine production have become routine in several developed countries. Such schemes have mainly been introduced to reduce losses in animal production. However, they may become of increasing significance for projects for reducing the risk of infections by "hidden" agents, such as invasive Salmonella spp., and other enterobacteriaceae, toxoplasma, Q-fever, respiratory infections, etc.

 

bb) In birds SPF programme consists in selection of healthy flocks confirmed by a complex of clinical, epizootiological and laboratory investigations including the history of the flock origin. Fertile eggs are strictly controlled from microbiological point of view using sampling methods, disinfected and placed in sterile environment of incubators. The hatched birds are immediately placed in a pathogen-free space.

 

    Example: This method is used in poultry to create the flocks free of specific diseases such as mycoplasmosis, Newcastle disease, infectious bronchitis, salmonellosis, Marek's disease, etc.

 

24.3 Creation of new healthy herds/flocks

 

24.3.1 In new places

 

a) The best occasion for creating new healthy herds/flocks offers the establishment of completely new facilities and function of breeding or production units such as farms, ranches, etc. if they are populated from the very beginning by healthy  animals only.

 

b) The selection of animals for initiating new herds or flocks is extraordinary demanding. First is to select areas free of specific diseases and then epizootiologically healthy ranches and farms. From these places the groups of healthy young animals of the best productivity are formed and investigated. These investigations have decisive importance to avoid any affected animal to be introduced in new established premises. Selected animals should be isolated and observed during a determined period before moving them to a new place (quarantine).

 

c) It is obvious that the new facilities must be prepared and kept in very good hygienic standard, disinfected and protected against introduction of etiological agents.

 

24.3.2 In depopulated places

 

a) Repopulation of places depopulated due to eradication measures gives similar chance to start with new herds/flocks of healthy animals.

 

b) First condition is to be sure that the former focus area is completely free of specific etiological agents of the disease which has been eradicated (after so called "observation period" and final sanitation).

 

c) The selection, observation and protection of animals to be used for the repopulation are similar as in the case of starting new herds/flocks (see above).

 

24.3.3 Declaration of disease free herds/flocks

 

a) In practice the declaration of disease free herds and flocks is limited to selected infection diseases, first the most dangerous emergency diseases and diseases of major trade importance.

 

b) Before declaring any herd or flock as specific disease free, epizootiological situation is to be investigated and analyzed using the results of a complex of specific diagnostic methods.

 

c) Basic condition is that the herd or flock during a determined period has been free of the specific disease, i.e. prevalence rates of specifically healthy animals have been of 1.0 value (prevalence and incidence rates of specifically diseased animals as well as specific nidality have been of zero value).

 

   Example: International requirements for declaring sheep flock free from ovine brucellosis (B.melitensis): the flock be under official veterinary control, all sheep showed no clinical evidence of ovine brucellosis during the past year, all sheep are identified with permanent mark.

 

d) As specific disease free can be declared herd or flock in which the specific disease has never occurred and no any suspect cases have been discovered. However, in any case a particular epizootiological investigation is a must.

 

e) As specific disease free can be declared herd or flock in which this disease has been eradicated and during a sufficiently long observation period  the absence of diseased and suspect animals as well as of other sources of specific etiological agents has been confirmed.

 

f) Herds and flocks declared as specific disease free must be systematically controlled using respective diagnostic methods to reconfirm the disease free status and be protected using a complex of preventive methods.(See chapters 25 and 26).

 

   Example: International requirements for declaring cattle herd officially free from bovine tuberculosis: all cattle in the herd show no clinical sign of bovine tuberculosis; over six weeks of age, have shown negative result to at least two tuberculin tests carried out at an interval of six months, the first test being at six months following the slaughter of the last affected animal; showed negative result to an annual tuberculin test to ensure the continuing absence of bovine tuberculosis.

 

g) For official declaration of specific disease free status exist different legislative norms at national and international levels. For international trade purposes OIE International Animal Health Code is used.(See chapter 27).

 

24.4 Creation of specific disease free zones

 

a) Creation of specific disease free zones (areas) is similar as the creation of specific diseases free herds and flocks. This measures can be applied to depopulated zones and zones after a specific disease has been eradicated.

 

b) In the zones where no cases of a specific disease have been found for a longer time, a complex investigation of specific epizootiological situation using adequate tests in sample size representing the population must be carried out with negative results.(See also chapters 18 and 20).

 

c) In other cases is the need first to eradicate the disease, confirm the disease free status by particular investigations and ensure the protection of this territory against the reintroduction of specific etiological agents.(See chapters 27,28 and 29).

 

   The strategy is to create first smaller disease free areas and gradually to enlarge and unite them forming major territory with absence of specific disease.

   

 


 

25. GENERAL PREVENTIVE MEASURES IN ANIMAL POPULATION

====================================================

 

 

25.1 Introduction

 

a) General preventive measures protect healthy animal population, herds, flocks and individual animals against etiological agents and debilitating factors, strengthen animal resistance and protect healthy environment and specific disease-free zones and territories. Prevention is the first line of defense against a disease. The goals are to promote health, to preserve health and to restore health when it is impaired.

 

b) Preventive measures are those practices used to exclude a disease from a population of unaffected animals. It involves measures to exclude etiological agents from areas where it is not present and measures to protect animals when the disease is present within the geographical area and/or population (i.e. mass immunization, chemoprophylaxis, environmental control, hygiene, etc.).

 

c) Grade of exigency of preventive measures increases simultaneously with the grade of animal populations concentration and productivity, with the grade of epizootiological risk, grade of economic and public health importance of threatening diseases, grade of their propagation velocity, grade of animal susceptibility, proximity of the nearest foci and eventual links (contacts) with the affected animals or territories.

 

d) Graduation of preventive measures, ranging from almost no measures to very complex ones, also depends on a series of social and economic conditions. The most complex measures are applied to protect health of animals in highly concentrated and specialized enterprises with very intensive production.

 

   Therefore, complex preventive measures applicable for intensive large-scale production units (herd health programme for cattle or pigs or flock health programme for poultry) described below can serve as the model which should be adjusted to local conditions and needs.

 

25.2 Regulation of animal population breeding and production

 

25.2.1 Location of large-scale animal production units

 

  For new planned and/or being established breeding or/and production unit special requirements should be applied:

 

a) Protective zones varying from several hundred meters to several kilometres depending on size and importance of the unit, animal species and category and grade of epizootiological risk should be established:

 

- between the unit and nearest human habitation;

- between the unit and the other specialized animal units;

- between the unit and quarantine establishment;

- between the unit and nearest animal farm;

- between the unit and:  underground and surface sources of potable water; surface streams or natural and artificial reservoirs; slaughterhouses and meat processing plants; rendering plants; international airports and seaports; highways, major roads and railways with international traffic; industrial enterprises (depending on type and intensity of air pollution), etc.

 

b) The following conditions should be ensured:

 

- sufficient source of good  quality potable water;

- supply of animal feeds; for ruminants also arable land and/or grass land area;

- utilization of waste products, especially manure;

- electricity supply;

- proximity of communication;

- level of groundwater (at minimum 50 cm under the foundation of buildings).

 

c) The following aspects should be considered:

 

- risk of flooding or subsidence;

- epizootiological risk (risk of contaminated soil from previous animal keeping and buried carcasses, from inundations, etc.);

- risk of local foci with affected domestic animals by contagious diseases in the neighbourhood (affected-enzootic zone), risk of local natural foci among wild animals, risk of introduction etiological agents through vectors and reservoirs (arthropods, wild birds, etc.).

 

d) Preparatory investigations should be made before situating new large-scale animal production units and decision taken by respective local authorities.

 

25.2.2 Requirements for buildings and equipment

 

a) When projecting new buildings for large-scale animal production units the following is recommended:

 

- the buildings have to respect fully the physiology and ethology of the animals for which they are being prepared;

- the buildings have to create optimal conditions for animal rearing, reproduction and production;

- the buildings space and area (capacity) should correspond with physiological norms of space and area for one animal of a given species and category to avoid overcrowding;

- the buildings have to create optimal microclima during the whole year (during production process), particularly as far as light, air temperature, humidity, movement and contents are concerned, according to physiological requirements of the respective animals;

- the buildings should be provided with equipment for microclima measurement and automatic regulation;

- the building material used for the floor and walls should be disinfectable and wholesome for human and animal health.

 

b) The entrances should be provided with disinfection facilities for transport and personnel entering the premises.

 

c) The buildings and establishment zone for the animals - production zone should be isolated from the administrative, preparatory and storage buildings and entrance to the production zone should be only through the sanitary filter ("black and white system").

 

d) The area of the unit should be completely fenced.

 

e) The quarantine and isolation establishment should be out of the unit area or only on its edge.

 

f) A dead animals deposit or small necropsy room should be established on the edge of the unit so that the rendering plant vehicles do not need to enter the unit.

 

g) At the entrance of the production zone, a sanitary filter should be established where staff can change clothes and boots, and wash and disinfect themselves before entering and before leaving the unit.

 

h) Premises for the animals should be:

 

- constructed and equipped so that the proper and effective disinfection, control of insects and rodents can be carried out;

- protected against the penetration of insects, other arthropods, wild rodents, birds and free moving animals;

- equipped with suitable facilities for animal fixation, to enable veterinary interventions.

 

i) Pits and ponds for collection, storage and processing waste, particularly manure, should be built. Liquid manure should be stored in pond of impermeable construction to prevent contamination of ground and surface water.

 

25.2.3 Organization and management of large scale units

 

a) The unit's organization and management should fully respect all veterinary requirements, particularly as far as the technology, organization structure, production cycles and rhythms, supply and work organization are concerned.

 

b) The organization and management of the production process should ensure the separation in space of different categories (age, sex, weight) and animal groups from different sub-units.

 

c) An "all in-all out" system should be introduced and practiced (exception for dairy cows). The period between the following batches should be sufficient for effective cleaning and disinfection.

 

d) The closed herd system is strongly recommended as it minimizes risks of introducing infectious diseases into the unit. Adequate isolation facilities (quarantine) should be provided for bought-in stock.

 

e) Protection against many parasitic diseases in grazing animals consists also in particular grazing system such as mixed, alternate or sequential.

 

f) An identification system of the animals is to be established so that their origin can be traced, particularly when an infectious disease arises.

 

g) Records on all animals diseases and natural deaths, on the results of clinical and epizootiological investigations, findings from diagnostic laboratories, slaughterhouses, etc. should be kept at the unit and available for control and analysis if and when required.

 

h) The unit manpower should be skilled and well trained in applying management and feeding methods properly, in offering first aid to diseased animals, in reporting any animal disease and its suspicion to respective authorities and in assisting veterinarians when necessary.

 

i) Internal organization and working rules including animal health and hygiene measures should be cleared by local veterinary authority.

 

25.3 Animals selection, nutrition, management and hygiene

 

25.3.1 Animals selection

 

a) The animals to be selected for the large-scale production unit should be disease free and originate from herds free of transmissible diseases. The animals should be genetically, physiologically and morphologically suitable for intensive farming.

 

b) The favourable animal health status should be certified based on clinical and epizootiological examinations and on the relevant diagnostic laboratory tests (e.g. serological, parasitological, microbiological, etc.).

 

c) The animals selected for a unit should originate from one or very few (minimum) herds, preferably within a long-term programme to stabilize the relation between the unit and supplying units (minimize mixing of animals from different herds).

 

25.3.2 Animal nutrition, management and hygiene

 

a) A sufficient amount of feedstuffs, biologically wholesome and valuable and free of etiological agents, to be composed according to respective animal species and categories as well as grade/type of their exploitation. The ration, feeding technology, feed mixture concentrates and dietary constituents (feed additives, etc.) should be cleared by veterinary specialists.

 

b) Confusion between feedstuffs should be avoided. The necessary change of feedstuffs and feeding technology should be gradual and not sudden. Special attention should be paid to the transport and storage of feedstuffs if they are not produced locally. Plastic or paper bags are preferred (they can be burned while textile-made bags are usually reused).

 

c) Strict control of composition of feedstuffs is essential. An adequate monitoring programme in factories producing feed as well as the laboratory test of feedstuffs should be carried out. Precautions should be taken to avoid toxic hazards from substances used for sanitation (insecticides, disinfectants, etc.) when used improperly.

 

d) Water for animals should be drinking water only (corresponding to drinking water norms), natural or after suitable treatment. The amount should be ensure according to physiological requirements of the animals.

 

e) Periodic examination of feed and water should be carried out, especially for detection of biological and chemical agents dangerous to animal and human health.

 

f) Particular attention should be given to the animals of basic breeding herds. They should be healthy, free of transmissible diseases, genetic diseases, of anomalies and constitutional deficiencies. Their rations should be adjusted to the reproductive cycle requirements.

 

g) Cleaning, disinfection and control of insects and of damaging rodents should be regular and effective respecting the production cycle. Excessive dust should be kept under control (in poultry units a dust-free environment is necessary for all categories).

 

h) Manipulation with animals should be careful avoiding stress (.e.g. during fixing, regrouping, additions, etc.).

 

25.3.3 Animal transport hygiene

 

a) For animal transport, suitable arrangements should be made to preserve their health and to prevent the spread of transmissible diseases.

 

b) Loading and transportation should be carried out with a minimum of stress.

 

c) Vehicles should provide shelter against wind, rain, intensive sunshine, etc. especially for long journeys.

 

d) Trucks and railway wagons should never be overcrowded and hot, and should be designed to avoid injury to animals. At high temperature, a good ventilation of vehicles is essential to prevent heat exhaustion and death.

 

e) Transportation of new born animals (chicken, piglets, etc.) at low ambient temperature requires adequate warmth inside the vehicle, if necessary maintained by heating and ventilation. Animals on journeys lasting more than one day should be fed and watered daily.

 

f) After transportation the animals should be rested and watered. After a long journey between different climates, acclimatization is necessary for a few weeks to several months.

 

g) Animals should be loaded only into vehicles that have been thoroughly cleaned of substances which may be toxic or injurious to animals.

 

h) The vehicles should be cleaned and disinfected after transport of each batch of animals. Special attention should be paid to this procedure after shipping sick animals.

 

25.4 Animal health control and investigation

 

a) The unit animals should be under continuous and systematic health and productivity control carried out by the owners, attendants and technicians as well as by veterinary specialists during the whole production process and cycle.

 

b) The herd owner or attendant should inspect the entire herd at least once a day so that diseased animals are identified without delay. This can best be done at feeding time. The animals should be closely observed for occurrence of respiratory and enteric diseases. Special attention should be paid to the behaviour of animals, interest in feed and water, daily feed consumption and nutritional state, course of parturition, viability of new born animals, movements/walking etc.

 

c) Animals showing deviations from normal health, i.e. sickness and/or unthriftiness, should be identified, promptly removed and isolated and the veterinarian should be notified. Carcasses should be immediately isolated with strict sanitary precautions.

 

d) The veterinarian should examine suspect and diseased animals and if necessary institute measures to protect healthy stock. First, the possibility of an emergency disease must be checked!

 

e) All animals (mammals) dying in a large-scale unit should be checked for anthrax and if negative should be necropsied either in special farm facilities (necropsy room) or in diagnostic laboratory eventually in rendering plant. Slaughter of one or more sick animals may be necessary to aid diagnosis. Animals passed for emergency slaughter must be also examine for evidence of disease. A small emergency slaughterhouse in a big unit is useful.

 

f) On the basis of clinical, pathomorphological and epizootiological findings the veterinarian should direct any further examinations necessary to confirm the tentative diagnosis. Once diagnosis is confirmed, he should, if necessary, improve measures on both diseased and healthy animals in individual sub-units and/or in the entire unit.

 

g) Special emphasis should be put on early diagnosis of subclinical diseases by regular testing. Selection of tests depends on local epizootiological risks.

 

h) The owner as well as field veterinarian are responsible for notifying the official authorities of notifiable disease outbreak or its suspicion.

 

i) In slaughterhouses all the animals must be veterinary investigated before and after slaughtering (meat inspection).

 

25.5 Prophylactic measures

 

25.5.1 Immunological status

 

a) An adequate uniform immunological status of the unit animals should be achieved and maintained by rearing them in groups, by avoiding the mixing of animals from other groups and from different origins and by ensuring that the new born animals receive a sufficient quantity of colostral and milk antibodies. Particular attention should be paid to the creation of new immunologically uniform batches and groups of animals from the reproductive herd.

 

b) A systematic vaccination programme should be established and carried out taking into account the immunological status of the unit animals and the risk related to the local epizootiological situation and to the eventual introduction of animals from other places.(See chapter 26).

 

c) Current recommendations are against vaccination of pregnant animals except in late pregnancy when inactivated vaccines may increase the level of colostral and milk antibodies to protect the offspring in the early postnatal period.

 

d) Immunological status can be temporarily supported by using immune sera for prevention of certain diseases or in sero-vaccination in combination with specific antigens.

 

25.5.2 Chemoprophylaxis

 

a) In accordance with the local animal health situation a chemoprophylaxis programme should be prepared.

 

b) The use of chemical substances, such as feed additives for mass prophylactic and therapeutic application, which could cause residues in the final animal product, must be subject a very careful decision. Different anti-parasitica, feed antibiotics, peroral therapeutics, etc. belong to this group.

 

c) Where the parasitic diseases are a problem, antiparasitic treatment should be applied, particularly in the reproductive herds and feedlots.

 

d) According to the objectives and forms the prophylaxis can be divided in defensive, offensive, medical, sanitary, etc.

 

25.6 Measures against the introduction of diseases

 

25.6.1 Measures against the introduction through animals

 

a) Breeding units should be as self-contained as possible.

 

b) If it is impossible to apply fully the closed herd system, then the introduction of new animals from other places should be reduced to a minimum (in number of animals and places of origin).

 

c) Only healthy animals from healthy herds with favourable epizootiological local conditions should be selected. An exception could be made in the case when the herd of animal origin has the same epizootiological situation as in the unit.

 

d) The stock being transported into a unit should be examined by a veterinarian in the unit of origin and/or loading place who issues a certificate indicating health conditions, freedom from evidence of disease and the favourable epizootiological situation in the area from which the animals originate.

 

   The animals should be certified free from transmissible diseases based on clinical and epizootiological examinations and on the relevant diagnostic laboratory tests (e.g. serological, parasitological, etc.).

 

e) The veterinarian of the receiving unit should first examine the animals and their certificates. Only when no any adverse problem is found then the stock should be unloaded. All the animals should be quarantined for adequate periods according to local conditions before they join the herd. During quarantine, the animals' health should be controlled regularly and eventually examined complementing clinical and epizootiological methods by laboratory testing.

 

f) Entry to the premises of any stray farm animals and birds, stray cats and dogs, as well as wild animals and birds should be prevented. Farm personnel should not be allowed to bring pets or other animals into the units.

 

g) Adequate safeguards against transmitting diseases by semen is best achieved by controlled artificial insemination.

 

25.6.2 Measures against the introduction through humans

 

a) Regular workers should not be recruited if they suffer from disease transmissible to animals. All workers should pass a medical examination on recruitment and should be re-examined regularly and whenever necessary. Workers suffering from a disease transmissible to animals should not work in the unit.

 

b) The workers should change clothes (preferably including undergarments) in dressing rooms situated conveniently near the unit entrance. Dressing  rooms, separated for men and women, should be equipped with boxes for personal and protective garments, showers, washbasins and toilets. Workers should move between the sub-units in minimal frequency. Administrative employees should wear overalls and overshoes when entering animal accommodation.

 

c) Mats soaked with an approved disinfectant should be placed in front of the entrance to each sub-unit, and a supply of water for cleaning and washing should be available inside the buildings. Shoes or boots should be washed and disinfected at the end of each working day and overalls and undergarments used at work should be changed at least once a week and washed in the unit or safely elsewhere.

 

d) Seasonal (occasional) workers should be informed of all hygienic measures to be observed. The management should provide them with boots, overalls and other protective clothing as necessary. Within the unit, they should be restricted to the area necessary for their work.

 

e) Visits to large-scale units should be discouraged and should be permitted only when authorized by the veterinarian. New technology and management systems should be demonstrated by documentation (e.g. video) to avoid visits to animal buildings.

 

   No visitor should be permitted to enter a unit:

 

- when epizootic diseases have been confirmed on the farm or in the neighbouring area;

- if they have visited another livestock unit within the previous days;

- if they are from abroad and their stay in the country has been very short;

- if they are from a country affected with most dangerous diseases (e.g. foot-and-mouth disease).

 

   Visitors who are permitted to enter a large-scale unit should observe similar hygienic precautions to those of regular workers. The best is to use the "shop window system".

 

f) Unit personnel should not rear their own animals at home unless accepted as being of no risk to the unit's animals.

 

g) The management should supply meals and refreshment for the entire staff to avoid the units workers bringing in food.

 

25.6.3 Measures against introduction through transport means

 

a) Transport to the unit of feeds, straw, equipment, etc. from places affected by transmissible diseases (notifiable) should be prevented.

 

b) In front of the unit, a wheel dip filled with disinfectant should be available for tire disinfection of vehicles driving in. The movement of drivers and accompanying persons should be restricted inside the unit.

 

c) The storehouses should be filled from outside the unit and the supplier's vehicle should not drive in.

 

d) Loading bays should be provided close to the entrance for the delivery and despatch of live animals.

 

e) Special vehicles, watertight and easy-to-clean, should be used for carcass disposal. These vehicles should on no account drive into the unit. Therefore, the carcasses should be stored in a separate building accessible not only from inside but also from outside the unit to avoid entry of the renderer's truck.

 

25.7 Preventive sanitation

 

     See chapter 31.

 


 

 

 

26. PROTECTION OF ANIMAL POPULATION SPECIFIC HEALTH

===================================================

 

 

26.1 Introduction

    

a)     Specific preventive measures protect animals, herds, flocks and territories free of specific disease against its etiological agents and strengthen specific animal resistance.

 

   Specific preventive measure complement general measures as described in previous chapter 25.

 

b) In order to apply correctly specific preventive measures space and time delimitation between specifically healthy and diseased animals and between specific disease free and affected herds, flocks and territories is a must. This can be done only using a complex of investigation methods (see chapter 18).

 

c) There are different protection methods targeted against specific diseases. Beside the special regulation of animal breeding and production, sanitation methods against specific etiological agents (see chapter 31), application of specific prophylactic treatments (e.g. specific hyperimmune serum, selected antibiotics), measures against the introduction of specific etiological agents (see chapter 25) and control of their vectors and wild reservoirs (see chapter 31), the key role has the reinforcement of specific resistance.

 

26.2 Reinforcement of specific resistance

 

26.2.1 Genetic methods

 

a) Genetic improvement policy should be oriented also to strengthen general and specific resistance of animals. Modification of host resistance is based on the presumption that certain breeds and lines of animals are more resistant to  development of certain diseases than others. 

 

b) Genetic methods for the reinforcement of the resistance against specific diseases are based on the genetic selection and crossing of animals with the particular aim to achieve higher population resistance in the population.

 

c) For the reproduction the animals with higher resistance against specific disease than the others should be selected, i.e. to select stock that tends to be resistant to certain diseases.

 

d) The use of resistance breeds and stocks against some diseases is preferable.

 

e) Genetic engineering combined with selective breeding is promising for the future. At present, there is great interest in producing both transgenic animals in which genes for resistance are inserted.

 

26.2.2 Active immunological methods (vaccination)

 

a) Immunization (vaccination) represents the protection of susceptible individuals against transmissible diseases by administration of vaccine , i.e. living modified agents, suspension of killed organisms, or an inactivated toxin. The vaccine is capable of stimulating immune response by the host, who is thus rendered resistant to infection.

 

   Premunition signifies a state of resistance in a host harbouring a parasite, to superinfection by a parasite of the same species. This state is dependent on the continued survival of parasites in the body and disappears after their elimination.

 

b) Specific vaccination represents one of the most important components of a complex of specific protective measures in many infectious diseases. Mass vaccination, as a means of specific animal health protection, has to be well prepared and planned and should take into consideration a series of factors such as:

 

- specific epizootiological situation in the given area and in its neighbourhood;

- grade of specific epizootiological risk;

- species and number of exposed susceptible animals;

- type and effectiveness of available vaccines;

- space and time factors;

- effectiveness of other measures;

- expected cost/benefit ratio; etc.

 

c) First, it is necessary to define well the objectives which should be reached, i.e. to avoid originating a specific epizootic process and its developing in a given area or territory.

 

d) Selection of the vaccines should correspond fully with the specificity of etiological agents (specific disease) and their type (eventually subtype) threatening the given animal population. Animal species and categories to be vaccinated are to be determined according their susceptibility to respective specific etiological agents.

 

e) A further step is to determine the places (territory) of specific epizootiological risk, the herds, flocks or populations and the minimal animal number and proportion of them to be vaccinated. Sometimes only the epizootiologically and economically most important herds are selected for vaccination. In order to obtain effective protection is a tendency to reach the maximum possible vaccination coverage (proportion of vaccinated animals).

 

   Most large-scale outbreaks of contact transmitted infectious disease could be prevented if 70-80% of the population are immune.

 

f) The vaccination programme should also respect epizootiological categories of the animal population to be vaccinated. In this respect vaccination can be divided in:

 

aa) Territorial (total) vaccination which includes all susceptible animals or all animals of selected species and categories in a given territory; this type of vaccination is used against ubiquitous enzootic infections (e.g. swine erysipelas) or against highly dangerous diseases able to be transformed into a panzootic wave (e.g. foot-and-mouth disease).

 

bb) Zonal vaccination is used in threatened areas creating immune (buffer) zones to protect the animal population against potential panzootic wave, in border regions against epizootic threat from neighbouring countries, in districts around international ports and airports, international tourist centres, factories processing products of animal origin (local or imported), rendering plants, in the proximity of grand transit centres and routes, etc.

 

    Example: Buffer zone against foot-and-mouth disease in border areas of Greece, Bulgaria and Turkey protecting European territory.

 

cc) Perifocal vaccination is used in areas directly threatened from specific foci to protect animals in herds or flocks neighbouring with the foci. The range of the area depends on the character of disease propagation (vectorial transmission of diseases needs a wider zone), on epizootiological intensity (threat) of foci, on their number, size, location, etc.

 

dd) Intrafocal vaccination is used within the foci of specific diseases transmissible by contacts, i.e. in animals suspected of being infected but without presenting specific clinical symptoms. In these cases life vaccine provoking the immunity in a shorter time saving a good part of animals is preferable.

    Example: Use a life vaccine in early detected foci of Newcastle disease in large-scale poultry unit.

 

ee) Selective vaccination is limited to the herds or groups of animals selected from the point of view of epizootiological risk (the most exposed animals) and according to economic importance (the most valuable animals). This type of vaccination is applied also in herds with very weak preventive (protective) measures and in those which are supplied by animals originated from herds of different epizootiological situations.

 

ff) Mosaic vaccination is based on the combination (alternating) of areas vaccinated and not vaccinated forming a "mosaic" with the purpose of avoiding the onset of a panzootic wave, i.e. epizootiological and economic catastrophe in a given territory.

 

g) Systematic immunization creates an "immune barrier" which avoids the onset of panzootic waves and, generally, also of epizootic. However, it cannot often impede completely new sporadic cases and eventually local foci. This is because  in the majority of immunization programmes not all animals of susceptible species are vaccinated (not speaking of animals which are not presented to the vaccination by mistake or deliberately). In addition, the effectiveness of the immunization cannot be absolute and therefore almost always a part of the vaccinated animals can remain specifically susceptible (particularly the animals not being in good physiological status during the vaccination). This is the reason why together with immunization the other respective preventive/protective measures are to be applied.

 

h) Horizontal and vertical movement of the vaccinated population should always be taken into account as well as the new generation which has not yet been vaccinated and also the duration of postvaccination immunity. According to the risk duration  a complementary vaccination of newly introduced and new born animals and revaccination of the vaccinated animals is usually necessary.

 

i) In some territories where particular disease does not exist or only appears sporadically and where the radical "stamping out" methods is used, specific immunization can be limited or prohibited. There are different reasons for this:

 

aa) fear of "covering" the animals-carriers of etiological agents and the foci due to the block of disease development in immunized animals; in animal populations with a certain grade of immunity, the etiological agents cannot provoke clinically manifest forms, but can create latent carriers;

 

bb) fear of "covering" the epizootiological situation due to complication of the interpretation of diagnostic tests results when e.g. antibodies of vaccinated and naturally infected animals are often difficult or impossible to differentiate.

 

cc) low effectiveness of some vaccines or non desirable post-applicative reactions (local or total) in vaccinated animals (e.g. cases of postvaccination foot-and-mouth disease in the distant past due to errors during vaccine preparation).

 

dd) risk of spreading disease due to reversion to virulence (in the case of a modified live vaccine) or by creating carrier animals.

 

j) Different vaccination schemes are carried out according to: epizootiological situation, type of epizootiological risk, species and categories of animals to be vaccinated, local conditions and feasibility criteria, availability of funds, cost/benefit as well as the instructions on indication, contraindication and doses provided by vaccine producers.

 

   Priority is given the most threatened categories in which the immunity should be sufficient for a long period (e.g. up to end of fattening, in reproductive animals during the entire life, etc.). Population (territorial) vaccination is usually carried out seasonally (e.g. spring vaccination campaigns considering the disease seasonality and veterinary services activities cycles).

 

   It is preferable to vaccinate the animals at critical places and moments of breeding and production processes (when moving from one place to another, change in age or production category, change within the life cycle or production cycle, in quarantine, etc.). In this way  unnecessary disturbances of animals during the proper production periods can be avoided.

 

k) The schemes should avoid the accumulation or interference of different immunizations with exception of polyvalent vaccination using different vaccines together in the same animals.

 

l) Vaccine effectivity can be negatively influenced by low proportion of immune-competent animals in the population, by inappropriate maintenance of the vaccine (inadequate storage      temperature, elapsed expiration period), sub-dosification, etc.

 

m) Economic aspects play an important role when the decision to vaccinate should be made. Vaccination may be used initially before the eradication programme is actually in effect or secondarily as a control precaution.  It should also be considered if the vaccine will affect the epizootiology of the disease in a manner that would interfere with eradication measures. This problem is true for diseases that are detected by antibodies.

 

  Example: In vaccinating  cows against Brucella abortus it would not be determinable at a later date if they had been infected or vaccinated; this vaccination very often causes the underestimation and postponement of demanding radical measures for final eradication, i.e. using the easiest way but not the most effective one.

 

  The vaccination is usually used where and when the disease is widespread (enzootic) or increasing in spite of  control measures, the technology and conditions to eradicate are not available and it does not cause subclinical or carrier states and does not interfere with disease detection.

 

n) Vaccination can be a powerful tool in the early stages of eradication when the incidence of disease is high. During this stage of the programme, an effective vaccine can be used to reduce the rate of spread and incidence of disease. The problems caused in diagnosis and creation of carrier states are usually not significant at this stage when compared with the problems the disease is causing. The problems caused by vaccination use may become important at a later stage and vaccination should be discontinued.

 

o) There is a need for banks of vaccines against the most dangerous diseases, to be established by veterinary authorities for emergency situations.

 

 

 

 


 

 

 

27. EPIZOOTIOLOGICAL PROTECTION OF COUNTRY TERRITORY

====================================================

 

 

27.1 Introduction

 

a) The protection of country territory against the introduction of animal diseases and in particular of exotic ones (not existing in the country) is the priority of any effective disease prevention strategy.

 

b) The main objective is to maintain exotic diseases free status of the country territory (exotic diseases are different for each country) and create favourable external conditions for livestock husbandry and contra-epizootic programmes.

 

c) The principles for the protection of disease free territory are similar as the protection of disease free areas (zones) as described in chapter 25. However, these measures are much more demanding and stricter when applied for national territory protection.

 

d) The best measures against the introduction of diseases through the animals or their products is to be self-sufficient in production of food of animal origin and thus avoid this type of import.

 

   In other cases there is a need for reducing this import as much as possible and under very strict protective veterinary conditions regarding the commodity identification, origin, investigation results, veterinary certificates (sanitary guarantee) and quarantine. The governments should have strict control over commodities imported into the country so that these animals and products do not bring in diseases not existing in national territory.

 

e) Protective measures are applied also in border zones to avoid risk of introduction of animal diseases from neighbouring countries. Ideal location have the island countries or countries protected by high mountains, big rivers, impenetrable forests, deserts etc.

 

f) There are internationally accepted lists of the most important diseases to which special attention should be given when importing animals and their products:

 

aa) "OIE List A" means the list of communicable diseases which have the potential for very serious and rapid spread, irrespective of national borders; which are of serious socio-economic or public health consequences and which are of major importance for international trade of animals and animal products.

 

    In 2000 following diseases were included in List A:

 

- foot-and-mouth disease

- vesicular stomatitis

- swine vesicular disease

- rinderpest

- peste des petits ruminants

- contagious bovine pleuropneumonia

- lumpy skin disease

- Rift Valley fever

- bluetongue

- sheep pox and goat pox

- African horse sickness

- African swine fever

- Classical swine fever (hog cholera)

- Highly pathogenic avian influenza

- Newcastle disease.

 

bb) "OIE List B" means the list of communicable disease which are considered to be of socio-economic and/or public health importance within countries and which are significant in the international trade of animals and animal products.

 

  In 2000 following diseases were included in the List B:

 

- Multiple species: anthrax, Aujeszky's disease, echinococcosis/hydatidosis, heartwater, leptospirosis, Q-fever, rabies, paratuberculosis, New Word screwworm (Cochliomyia hominivorax) and Old Word screwworm (Chrosomyia bezziana).

 

- Cattle diseases: bovine anaplasmosis, bovine babesiosis, bovine brucellosis (B. abortus), bovine genital campylobacteriosis, bovine tuberculosis (Mycobacterium bovum), cysticercosis (C.bovis), dermatophilosis, enzootic bovine leucosis, haemorrhagic septicaemia, infectious bovine rhinotracheitis/infectious pustular vulvovaginitis (IBR/IPV), theileriosis, trichomoniosis, trypanosomosis, malignant catarrh fever and bovine spongiform encephalopathy (BSE).

 

- Sheep and goat diseases: ovine epididymitis (Brucella ovis), caprine and ovine brucellosis (B.melitensis), caprine arthritis/encephalitis, contagious agalactia, contagious caprine pleuropneumonia, enzootic abortion of ewes (ovine chlamydiosis), ovine pulmonary adenomatosis, Nairobi sheep disease, salmonellosis (S.abortus ovis), scrapie and maedi-visna.

 

- Horse diseases: Contagious equine metritis, dourine, epizootic lymphangitis, equine encephalomyelitis (Eastern and Western), equine infectious anaemia, equine influenza, equine piroplasmosis, equine rhinopneumonitis, glanders, horse pox, equine viral arteritis, Japanese encephalitis, horse mange, surra (Trypanosoma evansi) and Venezuelan equine encephalomyelitis.

 

- Pig diseases: Atrophic rhinitis of swine, porcine cysticercosis (C.cellulosae), porcine brucellosis (B.suis), transmissible gastroenteritis of pigs, trichinellosis, enterovirus encephalomyelitis (Klobouk's disease, Teschen disease) and porcine reproductive and respiratory syndrome.

 

- Poultry diseases: Avian infectious bronchitis, avian infectious laryngotracheitis, avian tuberculosis, duck virus hepatitis, duck virus enteritis, fowl cholera, fowl pox, fowl typhoid (S.gallinarum), infectious bursal diseases (Gumboro disease), Marek's disease, avian mycoplasmosis (M.gallisepticum), avian chlamydiosis (psittacosis/ornithosis), pullorum disease (S.pullorum), Salmonella enteritidis and Salmonella typhimurium  in poultry.

 

- Lagomorph diseases: Myxomatosis, tularaemia and viral haemorrhagic disease of rabbits.

 

- Fish diseases: Viral haemorrhagic septicaemia, spring viraemia of carp, infectious haematopoietic necrosis, epizootic haematopoietic necrosis and Oncorhynchus mason virus disease.

 

- Mollusc diseases: Bonamiosis, haplosporidiosis, Perkinsosis, marteiliosis and microcytosis (Microcytos mackini).

 

- Bee diseases: Acariasis, American foul brood, European foul brood, nosemosis and varroasis.

 

- Crustacean diseases: Taura syndrom, white spot disease and yellowhead disease.

 

- Diseases of other animal species: Leishmaniasis.

 

cc) Other diseases internationally monitored are in the "FAO list C".

 

New OIE list has regrouped international notifiable diseases according to  animal species and not according to their importance.

 

27.2 Protective measures in national borders

 

27.2.1 At frontier posts

 

a) All frontier posts through which the import of animals and their products is permitted should be under veterinary control. These posts (in seaports, airports, railway stations, roads, etc.) are usually selected and published by the government  authorities. In their neighbourhoods no domestic animals should be reared.

 

b) At these posts veterinary inspection controls the certificates of importing (passing) animals and their products, investigate clinically all animals or controls other commodities of epizootiological risk (products, objects, transport means, etc.).

 

c) Only in the case when no any doubts about the certificates (must correspond with veterinary conditions for particular import) and about the disease free status the commodities are permitted to entry national territory. 

 

   In opposite case these commodities should be blocked and higher veterinary authority decides if they will be returned or treated under special conditions.

 

   The permission of importation should be refused and adequate protective measures should be applied, if the inspecting veterinarian reveals or gives substantial reasons to suspect that:

 

- the animals are affected with notifiable disease, or with symptoms attributable to such disease, or have been in contact with such animals;

- the products constitute a danger to human or animal health;

- official sanitary requirements or conditions of origin have not been complied with;

- the consignment of animals or products does not comply with official standards of health or quality;

- the official certificate is missing, defective, or not corresponding to the consignment;

- the identity or origin of the consignment are doubtful;

- deceptive practices have been used.

 

d) For the case of emergency or detection of a dangerous disease the facilities for transport means disinfection and other forms of sanitation (e.g. for incineration of confiscated commodities and wastes) should be available. 

 

e) Many countries free of exotic diseases prohibit  international passengers to bring with products of animal origin. If these products are found during frontier control they are confiscated and incinerated.

 

27.2.2 Measures in territory along the borders

 

a) The border zone is understood as under elevated epizootiological threat from neighbouring territories. Epizootiological measures against the penetration of animal diseases through the country borders line consist in very strict protective procedures described in chapter 25.

 

b) All anti-epizootic measures such as monitoring and surveillance investigations, vaccination programmes, protection of herds and zones, etc. are significantly reinforced.

 

c) In the zones under long-term epizootic threat special additional measures are applied creating so called "buffer zone" consisting of territorial total vaccinations against specific threatening disease, depopulation or reduction of animal density, reduction of domestic animals movement outside the farms, intensive epizootiological surveillance, etc.

 

d) In some cases of acute risk complete temporal closure of national borders against neighbouring country has been applied (against nearing wave of very dangerous disease such as foot-and-mouth disease).

 

27.3 Protective measures related to import of animals

     and their products

 

27.3.1 General principles

 

a) Protection of the national territory against the introduction of animal diseases is an essential task of any animal health service, which, for this purpose, should have the overall power to control the import of all live animals and products of animal origin.

 

b) Importing countries protective measures consist in:

 

- getting reliable information on exporting country epizootiological situation, control measures and veterinary services standard ;

- defining veterinary requirements for the import to be certified by exporting country;

- requirements for the transport;

- requirements for zoo-sanitary measures applicable before and at departure;

- requirements for zoo-sanitary measures applicable during the journey between the place of departure in the exporting country and the place of arrival in the importing country and in transit;

- requirements for zoo-sanitary measures on arrival.

 

c) Official veterinary export/import control should be exercised as consistent with bilateral and/or multilateral international commitments, in accordance with relevant rules and regulations, through appropriate measures.

 

27.3.2 Decision on import and epizootiological conditions

 

a) Decision on import of animals and animal products and on epizootiological conditions  is the duty of the central veterinary authority responsible for the protection of the country.

 

b) The decision depends on diseases introduction risk assessment, i.e. on evaluation of epizootiological situation in exporting and transit countries, comparing with the own situation, exporting country veterinary services level (ability of early detection of animal diseases, effectivity of their control, laboratory diagnostic standard), past experience with the export from the given country, risk of illegal reexport, etc.

 

c) The prohibition of importing from a given country is usually linked with bad epizootiological situation in exporting or transit country (e.g. existence of exotic diseases) or when exporting country is unable to meet importing country requirements.

 

d) In positive case special conditions are be defined respecting international agreements. Usually importing country requires that:

 

- the animals are in perfect health and the products in adequate quality i.e. free of etiological agents;

- the animals and products originate from country, territory, areas and places (herds) are free of particular communicable diseases during a given period;

- necessary investigations give negative results;

- eventually the animals are specifically vaccinated and/or treated.

 

e) For the cases of introduction of a disease, non corresponding certificates or doubtful results of control investigations (e.g. in quarantine) a special agreement on reclamation should complement veterinary conditions for import. This avoids troubles in solving these cases.

 

27.3.3 International certificates for export/import

 

a) International certificates should confirm that the importing countries veterinary conditions have been fully met and therefore the particular import can be carried out.

 

b) International zoo-sanitary certificate means a document issued by an official veterinarian of the exporting country, certifying the state of good health of the animals and giving particulars where applicable of the biological test(s) to which the animals have been subjected and the vaccination(s) carried out on the animals which are the subject of the certificate. This may be either individual or collective depending on the species of animals under consideration or the particular conditions of the shipment. This term also applies to a certificate covering semen, milk, embryos/ova, hatching eggs, fish eggs, brood-combs of bees, giving particulars of the measures taken to prevent the spread of epizootics.

 

c) International sanitary certificate means a document issued by an official veterinarian certifying the wholesomeness of meat, fish products or products of animal origin destined for human consumption, and when necessary, giving particulars of the measures taken to prevent the spread of epizootics. This term also applies to a certificate covering products of animal origin destined for use in animal feeding, or for pharmaceutical or industrial use, as well as biological products and pathological material.

 

d) The certificate should be issued  not earlier than three days before the loading if no other decision is made by importing country. The certificate form should respect international models and be bilingual using at least one international language.

 

27.3.4 Preparation for international export

 

a) The animals to be exported must be examined by a veterinarian in the origin/loading place who will issue a certificate indicating health conditions, freedom from evidence of disease and the favourable epizootiological situation in the area from which the animals originate.

 

b) The animals should be certified free from transmissible diseases based on clinical and epizootiological examinations and on the relevant diagnostic laboratory tests (e.g. serological, parasitological, etc.).

 

c) In major exporting countries particular quarantine stations have been built where the animals selected for export are investigated and treated to meet importing country requirements as best as possible.

 

d) In some cases the experts of importing countries visit exporting country to be better acquainted with the local situation and eventually to take part in the selection and investigation of herds and animals.

 

27.3.5 Measures in destination place

 

a) The veterinarians of the receiving units (the number to be minimal possible) will first examine the animals and their certificates. Only when no any adverse problem is found then the animals may be unloaded.

 

   All the animals should be quarantined for adequate periods (in animals for reproduction usually one month as minimum) according to local conditions and epizootiological situation before they join the herd. During quarantine, the animals' health should be controlled regularly  complementing clinical and epizootiological methods by laboratory testing.

 

b) The investigations during the post-import quarantine period should include at least the tests required by the importing conditions, i.e. to repeat them in order to reconfirm the negativity.

 

c) According to epizootiological situation and programmes imported animals in quarantine can be vaccinated, prophylactically treated (e.g. dehelminthization), etc.

 

d) Imported animals should be under special surveillance during the post-quarantine period to detect in time eventual latent carries not reacting positively during quarantine (e.g. cases of Brucella abortus detected 2-3 years after the importation of pregnant heifers when all previous tests were negative).

 

e) Imported meat and other products subject to official veterinary inspection after examination of veterinary certificates and identity of consignment should be investigated visually and organoleptically and in diagnostic laboratory (samples under suspicion, or on routine basis).

      

f) It is preferable to import animal products after being devitalized (e.g. sterilized) than in crude state. The distribution of imported crude animal products should be limited to the minimum possible places and outside of livestock husbandry area.

 


 

 

28. ANIMAL POPULATION GENERAL HEALTH RECOVERY

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28.1 Introduction

 

a) Measures for animal population general health recovery aim at the improvement and restoration of collective health of diseased (epizootiologically affected) herds, flocks and populations. General health recovery is the basis for specific health recovery measures oriented against particular diseases.

 

b) General health recovery procedures represent an integral component of epizootiological measures complex implementing epizootiological strategy aiming at the reduction and elimination of epizootiological risk and losses.

 

c) The objectives are the reduction of general (crude) morbidity values and increasing general (crude) "salubrity" values. Reducing of affected environment and territory belong among the objectives  as well.

 

d) Recovery measures can be complete or partial (covering only a part of affected population), primary (decisive) or secondary (complementary), oriented against disease causes or only against general morbidity consequences (e.g. reduce or avoid mortality due to diseases).

 

e) General health recovery programme should be carried out in any herd and flock, mainly in large-scale animal production units, having problems with lower productivity and reproductivity caused by  multietiological general (crude) morbidity. The best solution is to include the measures as the normal components of breeding and production processes, organization and management, i.e. avoiding as much as possible the disturbing "interferences" due to additional recovery measures.

 

f) The main criterion for the evaluation of general health recovery measures is improved productivity and reproductivity, better utilization of the inputs (e.g. feeds) and reduced losses due to general morbidity.

 

28.2 Correction of animal population breeding and production

 

a) General health recovery caused by multietiological complex of biological and non biological factors, including deficiencies in rearing animals and hygiene, asks first for corrections of animal life conditions.

 

b) The correction of animal environment and hygiene can be done applying prevention measures, as described in chapter 25, regarding animal location, concentration, organization and management of breeding and production, selection of animals, nutrition, hygiene, immunological status, chemoprophylaxis, measures against introduction of etiological agents, sanitation, veterinary control, etc.

 

 

c) One of the effective measures is speeded replacement of the population which gives the chance to replace quicker the old generation, usually with worse health than the health of new generation. This natural process, if well managed, can contribute itself to reduction of general morbidity and mortality.

 

d) Other general principle is to detect the suspect and diseased animals in time and to isolate them without any delay in separate place where they should be investigated by the veterinarian who decides what to do with these animals.

 

28.3 Resistance reinforcement and treatment of animals

 

a) Reinforcement of general resistance in affected herds/flocks and populations contributes to the reduction of general morbidity. The methods are described in chapter 25.

 

b) In the herds or flocks enzootically affected by a complex of biological etiological agents and conditional pathogens colostral immunity has an important recovery role. The immunity of animal-mothers gained under the local external and internal microflora conditions is able to contribute to the protection of the new born animals against these local microbiological complexes.

 

c) In the herds or flocks affected by an etiological complex, in particular with low level of hygiene and/or with mixed animals of different origin (i.e. different immunity status) the application of wide-spectrum chemoprophylactics can reduce general morbidity and mortality.

 

d) Traditional curative procedures oriented against clinical symptoms if applied massively are able to decrease the losses due to general morbidity and mortality. It is obvious that the etiologically oriented treatment against the disease causes is preferable.

 

e) When using the same prophylactic and curative  treatment for longer period attention should be given to the risk of the creation of resistant etiological agents strains complicating the future effectivity of this treatments. Only tested and approved prophylactics and curative drugs should be used respecting fully the producer's instructions.

 

28.4 Measures against etiological agents propagation

 

a) Measures against etiological agents propagation within the affected herds, flocks and areas prevent the worsening of the local epizootiological situation. Horizontal and vertical isolation of individual groups of animals, division of affected groups from "healthy" groups and isolation of any suspect and diseased animal are the basic methods. (See chapter 26).

 

   Reduction of contact is used to reduce or prevent direct or indirect contacts between infected and non-infected animals. Animals may be separated spatially (e.g. in different premises for cows and calves) or temporally (e.g. "all in-all out" poultry facilities).

 

b) Quarantine is the limitation of freedom of movement of diseased animals and of such animals as have been exposed to a transmissible disease for a period of time (the longest usual incubation period of the disease) in such manner as to prevent effective contact with those not so exposed.

 

c) Sanitation measures are indispensable. (See chapter 31).

 


 

 

 

29. ANIMAL POPULATION SPECIFIC HEALTH RECOVERY

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29.1 Introduction

 

a) Measures of animal population specific health recovery -  animal diseases control and eradication measures represent the activities aiming at the improvement and recovery (reestablishment) of animal health of affected herds, flocks and populations, as well as specific disease-free status of previously affected environment, areas and territories.

 

b) The disease control and eradication (further is used "control" only for both terms) as an integral component of antiepizootic measures complex aims at reduction and elimination of specific epizootiological risks for healthy herds, flocks and populations as well as zoonoses risks for human.

 

   These measures can be operational in cases of new individual outbreaks or programmed in cases of affected population or territory recovery (control programme).

 

c) Disease control measures can be oriented to the reduction and elimination of etiological agents and/or to the reduction and elimination of clinical cases and other negative consequences (such as mortality).

 

d) To achieve necessary effectiveness disease control measures should be applied during the whole period of the actions against given diseases as well as in all places with affected and threatened animals and environment.

 

e) To apply disease control measures correctly, the limits between diseased and healthy animals, affected and not affected places, territories and environment should be well determined dividing preventive and recovery measures. This requires demanding investigation activities before and during all programme phases.

 

f) To reduce and avoid new cases and foci the protection of healthy animals, herds, flocks and populations at risk is a must. Therefore, the isolation of the animals that are either infected or suspected of being so should be applied.

 

g) The disease control measures should be well adjusted to the specific nature of a given disease, its situation and development stage respecting influencing conditions and factors.

 

h) Disease control measures can be subdivided in conservative - based on curative treatment and/or vaccination and radical - based on detection and elimination of diseased animals (e.g. test and slaughter).

 

i) The control programmes have different phases:

 

-  In the preparatory phase,  personnel are trained,  the supply  of  local services is assessed and programme organization and administration is  put into  place.

-  In the attack phase, the area‑wide directed activity against the disease commences.

-  In the execution phase the control actions complex is implemented.

-  In the maintenance  phase consolidating the results after achieving the objectives is applied intensive surveillance for remaining cases and the traceback of all cases to ensure that the original source and all contacts of  the case are detected and controlled.

-  In the final phase  of eradication surveillance in preventing the reintroduction  of  the disease and  developing an early warning system for such introduction should be carried out.

 

29.2 Objectives of specific health recovery

 

29.2.1 Introduction

 

a) Gradual, i.e. in stages (step-by-step) and zone-wise, "cleaning" of animal population from all economically and public health important diseases represents the general programme of the recovery policy.

 

b) Basic objectives express either gradual increase of specific "salubrity" rates values up to 1.0 or gradual reduction of specific morbidity rates values down to 0.0. The objectives are closely related to a gradual increase of the number of specifically healthy herds, flocks and specific disease-free areas, i.e., on the contrary, a gradual reduction of the number of foci (nidality rates) and of affected areas (size).

 

c) The objectives can be expressed not only in terms of epizootiological indicators but also in economic terms (e.g. reduced milk losses in litres), in public health terms (i.e. reduced incidence in humans) and eventually in ecological terms (e.g. increased population of rare wild animals).

 

d) Principal grades of control objectives are: detaining, reduction, elimination and eradication of specific diseases.

 

29.2.2  Detaining of specific morbidity

 

a) The first grade  of  disease  control  objectives  is to detain specific animal morbidity and epizootic process. Detaining means to avoid  further increase of morbidity  values, eventually also the values of specific nidality and to limit or stop further propagation of the given etiological agents.

 

b) The balance  between the number of  new diseased animals and  extinct diseased  animals (by death, slaughter, recovery, remove, etc.) is maintained.

 

c) The  value of  point prevalence rate by  the end of  a given period is about the same as the initial one.

 

29.2.3  Reduction of specific morbidity

  

a) The second grade of control objectives is to reduce specific animal morbidity to a certain acceptable level and to improve the epizootiological situation.

 

b) Morbidity reduction is generally linked with specific mortality and nidality  reduction  as  well  as   affected   areas (territory) reduction.  Usually point prevalence rates of diseased animals, affected herds or foci are used for the formulation of control programme objectives and for the evaluation of the results in chronic diseases and incidence rates in acute diseases. In enzootic diseases territorial indicators such as absolute and relative values of affected areas (zones) in surface measure units are used.

 

c) To  achieve  reduction  of  specific  disease occurrence active,  intensive  and demanding  complex  measures  need  to be applied.

 

d) Reduction of  disease  morbidity  is  the  most frequent objective of specific diseases control programmes.

 

29.2.4  Elimination of specific disease

 

   Elimination of specific disease represents the achievement and maintenance of zero value of specific morbidity expressed in terms of point prevalence rates. Incidence rate has not yet reached zero value.

 

   Elimination, however does not mean the extinction of specific etiological agents in the given place or territory. These agents still survive within different sources (undetected animals-carriers, vectors, infected or contaminated products, environment, etc.). Therefore there can be newly detected cases of diseased animals which should be immediately eliminated.

 

29.2.5 Eradication of specific disease

 

   Eradication of specific disease represents the achievement and maintenance of zero value of morbidity in terms not only of prevalence rate but also of incidence rate and specific nidality rate. The disappearance (or devitalization) of all specific etiological agents in a given territory is complete. Shortly, the eradication refers to the extinction (extermination) of specific infectious agents in a given herd, flock, population or territory. (Measures see in 29.6).

 

29.3 Outbreaks discovery and first measures

 

a) An outbreak is a series of new cases of a disease clustered in time and in space or occurring at a higher frequency (rate) than what is normally expected. The effectiveness of control measures depends greatly on timely discovery of outbreaks of specific disease and correct determination of their limits.

 

   The obligation to report notifiable and diseases included in animal health programmes and suspicion of them to the respective veterinary authority should be assured by legislation.

 

b) Veterinary officer who receives the notice of suspect case of a notifiable disease (see chapter 19) should be obliged to proceed without delay to the place concerned and to ascertain the fact on the spot. Such visit should be free of charge to the owner of the suspected animals or carcasses. In the areas of extensive livestock husbandry where the immediate visit by a veterinary officer is not always feasible, the preliminary investigation may be entrusted to private veterinarian.

 

c) At the site of occurrence the first steps should be:

 

- examination of the suspected animals or carcasses concerned;

- clinical examination of other susceptible animals in the place concerned;

- submission of samples for laboratory examination and/or diagnostic tests;

- determination of the extent and limits of the infected place, and number of animals therein, for the purpose of immediate precautionary measures and subsequent sanitary action.

 

d) Unless the ascertaining of facts provides convincing evidence that the symptoms observed (findings) are not attributable to a notifiable disease, the veterinarian should take immediate precautionary (provisional) measures, which should be designed, applied and effectively enforced as consistent with the nature of the disease suspected and suitable for the purpose of preventing spread. In particular such measures should provide for:

 

- preventing of removal of any animals or objects capable of transmitting the disease from the infected or suspected infected place;

- identification of susceptible animals in the place;

- prohibition of entry of unauthorized persons or introduction of animals to the place;

- equipment such as buckets, brushes, scrapers, disinfectants and spray pump should be made available at the gate for cleaning and disinfecting personnel, trucks and other equipment leaving the premises;

- adequate instructions of the livestock owners or tenants as to the handling of the affected animals, litter, dung and manure, and other pertinent precautions which they should be obliged to observe.

 

e) The initial epizootiological analysis should be aimed at the investigation of the origin and possible spread of the infection, in particular by:

 

- thorough inquiry on any recent movement of animals or products capable of transmitting the disease to the infected place and from such place, including where appropriate the movement of persons;

- adequate inspection at the places of origin and destination thus determined;

- clinical examination of susceptible animals in the surrounding area.

 

29.4 Further investigation of the outbreak

 

a) Objectives of outbreak investigation following the first steps described above are:

 

-  etiological diagnosis - tentative and final (suspicion confirmed or rejected);

-  epizootiological diagnosis (determine epizootiological situation and its characteristics).

 

   It is obvious that it must be confirmed that the problem is an outbreak (epizootic - certain number of diseased animals can be expected) or not.

 

b) Tasks of the epizootiological investigation to be able to determine epizootiological diagnosis:

 

- determine the limits of affected place, perifocal area, threatened zone and "tampon" zone (territorial epizootiological structure);

- determine the sources of etiological agents (affected animals, feeds, products, etc.);

- determine the origin of the disease (trace back survey);

- determine the time and way of disease introduction;

- determine the forms and ways of transmission;

- determine the propagation inside and outside of the outbreak area;

- evaluate previous situation in this area;

- evaluate epizootiological situation in surrounding area;

- identify animals and other potential sources of etiological agents for collection of specimens for laboratory tests;

- identify animals for clinical examination, for treatment, for slaughter and for isolation;

- determine epizootiological structure of animal population (affected, suspected, contact, at risk, susceptible and resistant animals);

- determine epizootic process form, grade, stage, tendency, prognosis and influencing factors;

- orientate diagnostic test procedure and results interpretation in laboratories;

- indicate the need for vaccine application; etc.

  

c) The cases can be defined in several ways: clinical, subclinical (requires field and/or laboratory tests to discover antibodies or agents) and/or according to non-specific signs that may be associated with the disease (e.g. decreased production, etc.). The other animals must also be verified by the same criteria as the cases.

 

d) This investigation relies on the premise that cases of a disease are usually not distributed randomly in a population but rather occur in certain patterns:

 

aa) Animal pattern exists mainly because of a natural or artificial susceptibility or resistance of groups of animals.  In outbreaks it is usually some resistance that protects the animals remaining well during the outbreak. Age, breed, sex, strain and genetics are the most frequently described host attributes. It is important to examine all the animals and determine the population-at-risk. Healthy animals should be examined first so the disease is not spread due to the investigator.

 

bb) The first case and temporal pattern may indicate the introduction time, incubation period, the duration of the disease and possibly the mode of transmission. To examine the temporal distribution of new cases, a graph should be drawn  with one or more epizootic curves using various time intervals that might be appropriate for the disease under study, e.g. hours, days, weeks. Its shape may reveal information about the nature of the epizootic (e.g. point or propagated epizootic) expressing the increase or decrease and speed of change.

 

cc) Characterization of the disease by location (spatial pattern) usually requires a topographic schemes (charts or maps) of the area or facilities indicating where the diseased and exposed animals were and are now located. The drawings help to analyze the interrelationships among cases and between the location of cases and other physical features.

 

e) The investigator should formulate and test (confirm or reject) a hypothesis as to the etiology, date of introduction, source, transmission, location and differential diagnosis. It is important to demonstrate that no other agents and mode of transmission is responsible for the disease. Further hypothesis testing is done by serology, epizootic curves, incubation period calculation, duration of disease and attack rate charts. Although laboratory results should not be discounted, a decision about possible cause and method of control may have to be made immediately if the disease spreads rapidly or the specific manifestation rate is high. Over the course of a longer period, the laboratory results and control measures will yield confirmation.

 

f) Not all steps are necessary in each outbreak. The measures within the framework of official rule and regulations should be designed and applied to suit the nature of each of diseases concerned and to meet the purposes of effective preventive measures, as appropriate under the circumstances and in view of the disease concerned.

 

29.5 Intrafocal and perifocal measures

 

   The below described general measures must be in any particular case adjusted to the specificity, risk and importance of the disease diagnosed or suspected and the local conditions in order to be selected the most appropriate and effective methods respecting official rules and regulations. The most complex and strict measures are applied in case of exotic diseases.

 

29.5.1 Intrafocal measures

 

a) Immediate precautionary measures, taken by the veterinarian at the site, should be confirmed or adjusted.

 

b) The outbreak place should be officially declared infected, or suspected to be infected, to the effect that pertinent legal provision apply to such place.

 

c) It should be announced to the public, through posters and other appropriate means, indicating the infected place, its exact limits, and relevant rules to be observed by the public.  

 

d) The initial intrafocal measures can be complemented by:

 

- intercurrent disinfection, cleaning, sterilization of swill, particularly residues of food and feed;

- diagnostic measures, collection of samples for diagnostic purposes and laboratory examination of such samples;

- prophylactic or therapeutic treatment of the animals, or prohibition of such treatment;

- slaughter or destruction of animals;

- disposal of dung, manure and litter;

- incineration, deep burial or confiscation for destruction of dead animal bodies; etc.

 

e) The spread of diseases requiring contact for transmission should be decreased and avoided through the  isolation of sick animals , i.e. separation, for the period of communicability, of infected animals from others, in such places and under such conditions as to prevent the direct or indirect conveyance of etiological agents from those infected to those who are susceptible or who may spread the agents to others.

 

f) Sanitary slaughter is the deliberate killing of animals infected, suspected of being infected or in contact with infected animals to stop disease spread. Slaughter may be selective, e.g. in "test and slaughter" where only test-positive animals are slaughtered. This technique is effective in slowly spreading diseases. The decision between slaughter   of only serologically or allergically positive animals and slaughter of affected herds is also dependent on the  prevalence, i.e. the  strategy  can be changed during one control programme, when a certain low level of the prevalence has been achieved and depopulation of whole herds can be afforded.

 

 Complete depopulation of herds or animals in defined areas is used for rapidly spreading diseases and/or diseases with serious consequences (see 29.6).

 

g) Chemoprophylaxis, i.e. the administration of a chemical, including antibiotics, to prevent the development of an infection or the progression of an infection to active manifest disease. Chemotherapy, on the other hand, refers to use of chemical to cure a clinically recognizable infectious diseases or to limit its further progress.

 

h) Biological control employs living organisms to combat disease.  Efforts to destroy the vectors as well as remove or control animal reservoirs that transmit specific etiological agents reduce the incidence of disease.

 

   Examples: screwworm control and eradication by release of sterile male flies. Removal of stray dogs and awareness of wildlife reservoirs has helped decrease the number of rabies cases in human population.

 

29.5.2 Perifocal measures

 

a) Where appropriate, and as consistent with the nature of the disease involved, following measures should be applied:

 

- designation of a perifocal zone (neighbouring with outbreak area), threatened zone (restricted - first protection zone) and "tampon" zone (observation - second protection zone) surrounding infected place, for the purpose of restriction, observation and other sanitary action as should be ordered in such area, with appropriate announcement to the public;

- for highly contagious and rapidly spreading diseases there should be following concentric zones: the infected place (outbreak and perifocal zone), the zone of movement prohibition (threatened zone) and the zone of intensive observation ("tampon" zone);

- immediate onset of sanitation action in the infected place, and where applicable, in the threatened and "tampon" zones.

- immediate onset of the epizootiological inquiry also in perifocal zones.

 

b) The measures in concentric zones surrounding the infected place and the criteria determining their size and limits should be designed and applied as consistent with the mode  of propagation of the given disease meeting the purposes of adequate prevention of spread. These measures should include, as applicable and appropriate:

 

- display of posters in conspicuous places and/or information by radio, television, press and other appropriate means to indicate the "restricted area" and/or "observation area", and to give pertinent instruction to the public;

- checkpoints and cordon fences as feasible and as appropriate for effective implementation of control measures;

- prohibition of animal markets, fairs, shows and other gatherings of susceptible animals;

- in particular cases, such as severe outbreaks of foot-and-mouth disease, also prohibition of major assemblies of persons and of markets also for non-susceptible animals, horse races, and similar events;

- prohibition of movement of animals and products capable of transmitting disease out of the area concerned;

- prohibition, restriction or limitation of the movement of animals and associated products within the area concerned;

- reinforced disinfection of vehicles;

- placing of disinfection mats at entry to premises and other suitable places;

- vector control, particularly insect control in the case of insect- transmitted diseases, and tick control in the case of tick-borne diseases;

- vaccination or prohibition of vaccination;

- intensified veterinary inspection, including identification of animals, systematic testing and clinical examination of susceptible animals, and related measures;

- compulsory pasteurization or boiling of milk and disinfection measures in dairy establishments;

- compulsory processing, sterilization or disinfection of products capable of transmitting the disease;

- specific measures, as applicable to certain diseases; etc.

 

c) Many diseases in which endogenous agents are incriminated are best controlled by alteration of other determinants, for example by improving hygiene.

 

29.6 Methods of animal disease eradication

 

a) The eradication of a newly introduced very dangerous exotic infectious disease requires very strict emergency programmes and measures. The eradication of diseases existing for longer period in a given territory requires usually long-term programme and measures.

 

   Effective eradication depends greatly of timely discovery of all specific foci and correct determination of their limits. Case detection and disease surveillance should be possible and feasible; and at least one tool effective in halting disease transmission must be available.

 

b) The eradication represents the follow-up of the disease reduction and elimination measures which has significantly reduced  the morbidity.

 

c) The main principle of eradication consists in elimination of all diseased animals through either slaughtering policy of affected and suspected animals (test and slaughter) or complete depopulation of all diseased, suspect and directly threatened susceptible animals at herd, flock or territory levels.

 

d) The slaughter policy can be applied as urgent measure in case of exotic diseases or gradually in case of chronic or enzootic diseases. The purpose of slaughtering of infected  and in-contact animals is to remove the main sources of infection.

 

e) To avoid the recidives (recurrence) or surprising later appearance of the given disease eradication programme requires very qualified investigation before starting and during the programme as well as during follow-up observation period. The eradication can be successful only if all existing foci and their perifocal zones and their limits are known and included in the programme.

 

   (Note: This is the reason why in some countries specific vaccination is prohibited due to disease 'covering' and diagnosis complications.)

 

f) Eradication procedure must be combined with very strict quarantine measures isolating and protecting specifically healthy herds and territories avoiding new cases and foci.

 

g) Eradication of an animal disease involves:

 

aa) selective slaughter is killing of infected animals to protect the majority. Selective slaughter has been and is presently used in many successful large scale campaigns against animal disease. Sometimes, however, the monetary costs outweigh the benefits due to the number of animals involved, disruption of the economy and the unavailability of replacement animals. Often the disease with very high prevalence is first decreased by mass immunization and later selective slaughter is used.

 

bb) Depopulation is the killing of entire herd or flock or population used in some very dangerous and exotic diseases. It is applied when a diagnostic test cannot be applied to an affected population in order to carry out selective slaughter; the population is inaccessible to perform other measures; the disease is spreading too rapidly to control by other methods; there are no other control methods available and depopulation of a specific herds or population is the only way to protect the neighbouring herds, flocks and populations (territories).

 

The depopulation includes:

 

- systematic slaughter of the entire susceptible animals population in the restricted area, or slaughter of particularly exposed sectors of such population;

- sanitary destruction, transformation or adequate processing of the carcasses;

- effectively enforced depopulation to be maintained during adequate periods of time, as consistent with the known length of survival of the etiological agents in the environment;

- subsequent repopulation effected under restriction and close official supervision.

 

cc) mass immunization to reduce the morbidity and losses followed by the proper depopulation of herds and/or flocks (still remaining infected animals in spite of the vaccination).

 

h) "Stamping-out" policy means the killing the animals which are affected in the herd and, where appropriate, those in other herds which have been exposed to infection by direct animal to animal contact, or by indirect contact of a kind likely to cause the transmission of etiological agents. All susceptible animals, vaccinated or non vaccinated on infected premises should be killed and the carcasses destroyed by burning or burial, or by any other methods which will eliminate the spread of infection through the carcasses or products of the animals killed. This policy should be accompanied by cleansing and disinfection.

 

i) Eradication of a disease having the only known reservoir and the agent is unstable in the heat, disinfectants and the environment is relatively easier than of diseases which etiological agents have a large wildlife reservoirs (e.g. rabies), persist very well in the environment and for long periods (e.g. anthrax), or are too ubiquitous (e.g. toxoplasma).

 

j) Several factors make disease eradication programmes perhaps less feasible now than in the past.  Among these factors are: increased constraints on governmental funding; increased concentration of livestock, creating possibilities of rapid spread to large numbers of livestock; environmental restrictions which complicate carcass disposal; and public sentiment which is less likely to accept slaughter as a means of disease eradication than formerly.

 

29.7 Measures during postfocal period

 

a) The infected place and surrounding zones should be released from restriction and an official declaration to that effect should be made, stating the end of the outbreak, when there is evidence that the etiological agents of the disease are no longer persisting in the place concerned, neither in animals nor in the environment.

 

b) To the extent to which the nature of the infected place permits and requires and where reasonable in view of the etiological agents concerned, terminal disinfection should be applied prior to release from restriction, including the incineration of presumably contaminated objects of low value which cannot be efficiently disinfected.

 

c) The infected place should be released from restriction if all infected animals have been slaughtered or died or recovered and if no further disease has occurred among the other susceptible animals following the last case of death or ascertained recovery during a certain length of time (observation period) as should be defined in accordance with known disease incubation and agents surviving periods. Tests of eventual "sentinel" animals have given negative results.

 

d) Appropriate precautionary measures of observation and movement control in the entire restricted area, including previously infected places should continue to be applied during adequate safeguard periods following the end of the outbreaks. This period should be defined by relevant rules and regulations and as consistent with known incubation periods, length of survival of the etiological agents in the environment, possible occurrence of clinically healthy carriers and other relevant factors, as applicable to each of the disease concerned and taking into consideration whether vaccination was practiced.

 

e) The release of the area from restrictions and intensified observation measures should be declared by an official statement and should be announced to the public.

 

f) Intensive epizootiological follow-up monitoring and surveillance should continue a longer period to be sure that no any source of specific etiological agents has remained in the recovered territory and populations.

 


 

 

30. MEASURES AGAINST DISEASES COMMON TO MAN AND ANIMALS

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30.1 Introduction

 

a) Protection of human health is one of the main priorities of any society. One of its components is the protection against diseases transmissible from animals. Therefore, in all specific diseases common to man and animals, called "zoonoses", the first priority measures consist in protection of human health.

 

b) Any discovery of a new case of zoonosis or new suspicion of it  in the animal population by veterinary service must be reported without delay to the respective public health authority. On the contrary, any finding of a zoonosis or suspicion of it in human population by public health service must be reported without delay to respective veterinary authority.

 

c) Common programmes against zoonoses are of particular importance for the achievement of desirable results in human and animal populations health protection and recovery. This is possible not only through control and eradication measures applied in animal population but also through epidemiological measures in human population based on  effective protection actions.

 

d) The epidemiological strategy and principles of measures are similar to epizootiological strategy and measures as described in chapter 23. The strategy against zoonoses should be common and the measures should be well coordinated.

 

30.2 Objectives of measures against common diseases

 

a) First priority of anti-zoonotic programmes is to avoid new cases of specific diseases in humans.

 

b) The objectives of common activities against zoonoses are:

 

aa) to maintain specific zoonosis-free animal and human populations, i.e. to keep zero values of specific morbidity in terms of prevalence and incidence (e.g. keeping animal population free of trichophytosis is the best specific protection of humans against this zoonosis);

 

bb) to reduce specific zoonosis in animal population and thus to reduce prevalence and incidence in human population to acceptable level (e.g. reduction of bovine tuberculosis reduces the number of new cases in humans);

 

cc) to eradicate specific zoonosis in animal population and thus to achieve also zero values of incidence in human population (e.g. eradication of brucellosis in animals avoids new cases in human population).

 

c) The objectives can be expressed also in terms of reducing zoonotic diseases consequences such as invalidity and mortality in humans due to specific diseases transmissible from animals (e.g. reduction of rabies in animals reduces and/or avoids death cases in human population). 

 

d) The objectives can be formulated also in terms of reducing zoonoses risk for human population (e.g. improvement of personal and environmental hygiene reduces the risk of persons employed in places exposed to animals and their products such as slaughterhouses).

 

30.3 Protection of animals against diseases from man

 

 In case of zoonoses the human protection is the priority, however, the risk of transmitting of zoonotic etiological agents from diseased humans to animals cannot be underestimated. Therefore, the measures against transmission from man to animals must be applied as well (e.g. avoiding the employment of persons suffering by pulmonary tuberculosis to be attendants of healthy animals). See chapters 25 and 26.

 

30.4 Protection of man against diseases from animals

 

a) To protect humans against zoonoses different measures should be applied according to the disease nature, human population resistance and local external conditions:

 

-  direct contacts of persons with alive, slaughtered and dead animals and their products (i.e. during animal rearing, animal products processing, etc.) should be avoided or limited as much as possible;

-  environment hygiene where the persons have direct or indirect contacts with animals and their products should be maintain at good level or improved;

-  common living of the persons together with animals under the same roof, i.e. in the same space (with exception of healthy pets under veterinary control) should be avoided;

-  consumption of crude food of animal origin should be avoided;

-  when working with animals and animal products protective clothes should be used and personal hygiene to be at good level;

-  technology of rearing animals and processing their products should limit the number of places and moments when the workers have to have direct contact with them;

-  ante mortem and post mortem veterinary inspection of slaughtered animals should be carried out (one of the most important measures to protect the consumers against diseases from animals);

- general pasteurization of milk before its consumption should be applied; etc.

 

b) Inside of zoonosis foci the above mentioned measures should be made a must.

 

c) The high level of hygiene during animal products processing, storing, transport and distributing is a requirement which can avoid secondary contamination by eventual zoonotic etiological agents from other part of the batch or from contaminated environment.

 

d) Other protection measures are oriented against zoonotic etiological agents vectors and reservoirs through avoiding or limiting entrance of them in dwelling and working places, using methods for personal protection, avoiding or limiting entrance of persons in areas of zoonotic diseases with natural nidality, etc. (See chapters 25 and 31).

 

e) Specific immunization of the exposed persons also belongs among important protection measures (e.g. of persons working in livestock husbandry, slaughterhouses, laboratories, areas of zoonotic diseases with natural nidality, etc.).

 

f) Reduction of animal populations and improvement of the environmental hygiene are other measures which can reduce the risk of diseases transmissible from animals.

 

30.5 Control measures in human population against zoonoses

 

a) Eventual new human cases should be detected in time and treated to safe the human life, return sick persons to full health as soon as possible or avoid serious consequences as much as possible.

 

b) The general control measures against zoonoses in human population including epidemiological investigations, reporting, analysis, monitoring, surveillance, immunization, treatment, isolation, disinfection, quarantine, etc. are described in human general epidemiology textbooks.

 

30.6 Cooperation between veterinary and public health services 

 

a) Control measures against zoonoses require close cooperation between antiepizootic measures, applied by veterinary services and antiepidemic measures applied by public health services.

 

b) All measures against zoonoses must be well coordinated and where and when possible applied commonly. Besides the coordination of antiepizootic and antiepidemic measures some of them can be done as common measures such as the sanitation in the same places, investigations of the specimens (e.g. serological test of human blood in veterinary laboratories, microbiological investigation of animal specimens in human laboratories, etc.), common surveillance, analysis, extension, training, legislation, rules, regulations, standards, instructions, scientific activities, etc..

 

c) Mixed commissions for the organization and coordination of the programmes against zoonoses at all levels of management have proved to have a key role in effective coordination and use of available resources. These commissions, usually composed of leading representatives of public health and veterinary services, and representatives of other relevant authorities deal with all zoonotic diseases. For selected specific zoonoses control programme of major importance a special coordination committee should be established.

 

 

d) In all cases mutual continuous information  on zoonoses situation in the human and animal population as well as on the applied measures should be provided.

 

 


 

 

31. EPIZOOTIOLOGICAL SANITATION

===============================

 

31.1 Introduction

 

a) Epizootiological sanitation is the provision of means whereby animal population health is protected through maintaining of etiological agents free environment, reducing and/or eliminating of etiological agents outside of alive animals, reducing and/or eliminating of their vectors and reservoirs.

 

b) Epizootiological sanitation is the component not only of preventive measures but also of control and eradication programmes. It contributes to decontamination (deactivation) of secondary sources of etiological agents, interruption of many ways of their transmission and improvement of hygienic conditions.

 

c) Among sanitation measures are included such activities as disinfection, disinfestation, control of rodents, disposal of dead animals, etc.

 

d) Sanitation measures should be applied in those epizootiological situations, places and time where and when corresponding effect can be expected considering the nature of particular etiological agents and environmental conditions.

 

e) Disinfectants and insecticides should be authorized only after thorough tests have been carried out under field conditions.

 

f) Detailed sanitation methods see in  zoohygiene textbooks.

 

31.2 Principles of epizootiological sanitation

 

31.2.1 Objectives of epizootiological sanitation

 

a) Final objectives of epizootiological sanitation coincide with the objectives of epizootiological programmes and measures.

 

b) The objectives can be general without taking into account specific etiological agents or specifically oriented against particular pathogens.

 

31.2.2 Preventive epizootiological sanitation

 

a) Preventive sanitation should be carried out regularly in all premises and facilities for animals giving priorities to critical places and time of breeding and processing process. Operational preventive sanitation is required when epizootiological risk is acute.

 

b) Preventive disinfection should be carried out systematically and should be included in all production processes. It is especially important in intensive large-scale units with a rapid turnover of dense animal population. The best results can be obtained under the "all in-all out" system, with thorough cleaning and disinfection in the absence of animals. Under continuous system, all temporarily vacant animal quarters, or at least a part of such as pens, stalls, etc. should be first cleaned and then disinfected with time given for this to take effect.

 

c) Insect control should be done in conjunction with preventive disinfection and its frequency depends upon the efficacy of the substance employed. All premises (animal quarters, feed and product storehouses, manure stores and all potential insect-breeding places) and their surroundings should be treated at regular interval with insecticides.

 

d) Rodent control should be applied continuously, using effective rodenticides and application methods. Human and animal intoxication risk must be prevented.

 

e) Regular collection and destruction of dead animal carcasses belong among important preventive sanitation measures.

 

f) Disease often results from a complex of factors in the causal web, many of which are related to environmental and management factors.  Alteration of one or more of these factors may reduce or eliminate disease transmission or development.

 

  Examples: washing and drying udders before milking, litter management in broiler houses, cleaning sows before farrowing, provision of adequate ventilation in animal housing, etc.).

 

31.2.3 Intrafocal sanitation

 

a) Intrafocal sanitation represents a very important component of control and eradication measures. Its purpose is to destroy all etiological agents existing outside of animal body, i.e. to reduce and eliminate intrafocal secondary sources and/or reduce and eliminate intrafocal vectors and/or reservoirs of etiological agents and thus to interrupt epizootiological chains.

 

b) According to the intrafocal phases of epizootic process following forms should be carried out:

 

aa) Initial intrafocal sanitation applied immediately after the detection a new focus.

 

bb) Concurrent intrafocal sanitation applied during the existence of the focus in different intervals to destroy or suppress etiological agents of secondary sources as soon as possible after being eliminated by diseased animals and reduce populations of vectors or wild animals-reservoirs in focus area. These measures help to block epizootic process development and shorten the duration of the focus period.

 

    Example: Concurrent disinfection is the application of disinfective measures as soon as possible after the discharge of infectious material from the body of infected animals, or after the soiling of articles with such infectious discharges.

 

cc) Terminal intrafocal sanitation applied at the end of the focus existence, after the last diseased animal has been removed by death or to the abattoir or to a distant isolation unit, or has ceased to be a source of infection, i.e. before declaration an outbreak to be liquidated and intrafocal measures to be finished. Its purpose is to destroy all etiological agents surviving after the recovery or elimination of the last diseased animal. This sanitation must be done very consequentially to be sure that the area is free of given specific etiological agents.

 

  This type of sanitation can have two phases, i.e. first immediately after eliminating the last diseased animal and second after the "observation period", i.e. before declaration of the area (herds, etc.) as specific disease-free.

 

31.2.4 Places of epizootiological sanitation

 

a) Epizootiological sanitation should be carried out in different places and in different intensity according to the needs of a given epizootiological situation and measures.

 

b) Sanitation can be applied in small spaces such as animal boxes, pens), in local areas (farms, ranches) up to major territories.

 

c) Disinfection is usually limited to animal installations and their neighbourhood while the measures against insect, rodents and other animals-reservoirs should cover much more extensive zone respecting their biology.

 

d) Space aspects of sanitation measures should be based on epizootiological analysis which should indicate the critical places and their limits requiring preventive or intrafocal actions. The sanitation to be effective should be well targeted to potential and/or real secondary sources representing epizootiological risk.

 

31.2.5 Time of epizootiological sanitation

 

a) Time aspects of sanitation measures should be based on epizootiological analysis which should indicate the critical moments and periods requiring preventive or intrafocal actions. The sanitation in order to be effective should be well targeted to potential and/or real epizootiological risk moments and periods.

 

b) Sanitation actions against insect-vectors and wild animals-reservoirs should respect the seasonality and live cycle of these beings.

 

31.3 Disinfection

 

  Disinfection is killing of infectious agents outside the body by chemical or physical means, directly applied.

 

31.3.1 Mechanical cleaning

 

a) Mechanical cleaning means the removal by scrubbing and washing, as with hot water, soap or suitable detergent, of infectious agents and of organic matter from surfaces on which and in which infectious agents may find favourable conditions for surviving or multiplying.

 

b) Before initiating cleaning operation, all contaminated areas and buildings should be sprayed with an approved disinfectant.

 

c) All buildings that could possible have been contaminated should be thoroughly cleaned: All straw, feed, loose litter and trash should be removed, burned and/or buried. Encrusted floors, walls and stalls should be scraped (dirt floors be scraped down to clean soil) and scrubbed. Provision should be made for directing wash water into a confined drainage system or ditch.

 

   Parts of buildings such as stalls, feed boxes, and wooden floors which are decayed or in such condition that cannot be thoroughly cleaned should be removed and burned. In some instances it may be necessary to destroy entire old buildings and their contents to ensure elimination of the etiological agents.

 

d) All manure and bedding that cannot be burned or buried should be composted with a layer of soil or a disinfectant (e.g. sodium carbonate) placed on the surface to protect from birds and insects. The compost area should be fenced to prevent livestock from gaining access. Manure should remain composted for a period corresponding to agents tenacity before it is spread in open fields.

 

e) The yard surrounding walls, fences, stables should be first sprayed with particular disinfectant, then scraped and scrubbed.

 

f) In hay, straw, crops and sacks of feed if contaminated by  dangerous agents all possibly contaminated areas should be destroyed by burning or burial. The surface of the remaining hay, straw, crops or sacks of feed should be then thoroughly sprayed with selected disinfectant.

 

g) Shoes, clothing, ropes, reins, curry combs, farm vehicles, personal cars, veterinary syringes, needles and other possibly contaminated items used in handling animals should be thoroughly cleaned, disinfected or fumigated or eventually destroyed.

 

h) All equipment used in material removal such as manure loaders, shovels, brushes and scrapers should be thoroughly cleaned. A cleaning agent (e.g. trisodium phosphate, sodium carbonate) should be used in the water.

 

31.3.3 Physical disinfection

 

  Physical disinfection can be done by dry heat (sterilization with high temperature), humid heat (boiling, pasteurization), burning, rays of sunlight, ultraviolet radiation, X-rays, etc.

 

  Example: Foot-and-mouth disease virus destruction procedures in meat: canning meat in tins subjected to heat treatment and sealed; cooking  meat, previously deboned and defatted; drying after salting (NaCl).

 

31.3.4 Chemical disinfection

 

a) When cleaning has been completed, the entire contaminated surfaces should be sprayed by approved disinfectant (using a power spray to get into cracks).  Bedding and litter as well as faecal matter should be thoroughly soaked with the disinfectant. When the floor of the building is composed of earth or is pervious to water, the surface should be broken and then also soaked with disinfectant similarly as other contaminated earth area.

 

b) Disinfectants are chemical substances used to destroy infectious etiological agents outside of animal body and thus to reduce risk of their transmission.

 

c) The choice of disinfectants and of procedure for disinfection should be made taking into account the causal agents of infection, the nature of the premises, vehicles and objects which are to be treated.

 

   Examples: Disinfectants recommended for the use against both hydrophilic and lipophilic viruses as well as unknown agents are: phenol, sodium hypochlorite and calcium hypochlorite.  Disinfectants recommended for use against lipophilic viruses and against many bacteria, rickettsia and protozoans are cresylic acid and sodium orthophenylphenate. Foot-and-mouth virus is easily destroyed by a high or low Ph but the disinfectants used may be caustic or corrosive in concentrated form. Tubercle bacillus is very resistant to disinfectants and a high concentration is required to destroy the organism, as well as prolonged action.

 

d) Few universal disinfectants exist. Whereas hypochlorite, which is very often used, may be regarded as a universal disinfectant, its effectiveness is diminished by prolonged storage and it is therefore necessary to check its activity before use. A concentration of 0.5 % active chlorine appears as satisfactory for disinfection.

 

31.4 Measures against vectors and reservoirs of etiological agents

 

31.4.1 Introduction

 

a) Disinfestation is any physical or chemical process serving to destroy or remove undesired small animal forms, particularly arthropods or rodents, present upon the animals or in the environment of the animals. (Synonyms include the term disinsection when insects only are involved).

 

   Fumigation is any process by which the killing of animal forms especially arthropods and rodents, is accomplished by the use of gaseous agents.

 

b) A knowledge of the habits of the vectors and/or reservoirs concerned is necessary to apply sanitation measures effectively. All premises (farms) in the  area should be treated and the wider the area covered, the more effective the disinfestation is likely to be.

 

c) Insecticides are any chemical substances used for the destruction of arthropods, whether applied as powder, liquid, atomized liquid, aerosol, or as a "paint" spray; residual action is usual. The terms larvicides are used to designate insecticides applied specifically for destruction of immature stages of arthropods; imagocides or adulticides, to designate those applied to destroy mature or adult forms.

 

d) Molluscicides are chemical substances used for the destruction of snails and other molluscs.

 

e) Repellents are chemicals applied to the skin or other places to discourage arthropods from alighting on and attacking the animals, and other agents, such as worm larvae, from penetrating the skin.

 

f) Possible development of the vectors or reservoirs resistance against disinfestation chemicals should be always taken into account.

 

31.4.2 Measures against insecta class vectors

 

a) The commonest method used in the past was to change insect habit conditions (e.g. cutting down the woody vegetation or drying water reservoirs) which provide the shade and/or resting and/or reproduction places necessary for the particular insect. Today, the commonest method is the use insecticides, applied either from the ground or from the air (aerial spraying and fogging using aeroplanes or helicopters).

 

  Example: Against tsetse fly in Africa the classical methods are complemented by the change of land use, bush clearing, game exclusion and game control ("game-proof" fences), using traps and experimental biological control (use of predators and parasites and sterile insect technique).

 

b) Application aim is normally to place droplets of insecticides on the parts of the vegetation or surface used by insect for its resting places. When the spray dries off, a thin film of insecticides is left which is enough to kill the insect if it settles on it.

 

c) Among insecticides belong organochlorines, organophosphates, carbamates, pyrethroids, etc. in form of water dispersible powders, emulsifiable concentrates or liquid concentrates.

 

31.4.3 Measures against arachnida class vectors

 

a) The most widely used effective method is the treatment of animals by dipping them or spraying them with natural or synthetic chemicals - acaricides (e.g. in ticks based on arsenic, chlorinated hydrocarbons, organophosphates, etc.). Animals may also be treated with acaricides applied as dust or smears and by other techniques (e.g. acaricide-impregnated ear tags, neck bands, leg bands, tail bands, "pour-ons", etc.). Arachnida can be controlled off the host by applying acaricides to the environment.

 

b) One of the form is habitat modification such as reduction in the vegetation cover, cultivation, zero-grazing and other agricultural practices affecting the infestation (e.g. rotational grazing interfering with host-findings, including in pastures, species and cultivars of the perennial legume Stylosanthes possessing glandular sticky hairs).

 

31.4.4 Measures using sterile insect technique

 

The sterile insect technique (SIT) involves mass rearing of the target pest species, sexual sterilization by radiation and the release of vast numbers of sterile insects into the infested area with a high ratio of sterile to wild (e.g. of 10:1 in screwworm). When a wild female mates with sterile male, she lays infertile eggs, and thus the offspring is not produced. Number of wild population and its reproductive capacity are consequently reduced and eventually extinct.

 

31.4.5 Control of wild animals-reservoirs of etiological agents

 

a) The measures against the wild animals-reservoirs of etiological agents aim at the elimination (depopulation) or reduction (rarefication) or repulsion of respective animal populations.

 

b) The measures are based on mechanical methods (e.g. traps, hunting), physical methods (e.g. flooding of burrows by water, filling them with vapour or toxic gas, etc.), chemical methods (solid or gaseous toxic substances used through baits), biological methods (using natural enemies - predators or parasites attacking the animals-reservoirs) and ecological methods (worsening the habitat and feed conditions for the animal-reservoirs).

 

c) The most frequent sanitation is carried out against harmful rodents (Rattus norvegicus, Rattus ratus, Mus musculus, Microtus arvalis, etc.). Rodenticides are chemical substances used for the destruction of rodents, generally through ingestion eventually fumigation. (When cleaning and disinfection operation are initiated, the rodents will migrate to other farms in search of food; an early survey should be made to determined the need for rodent control).

 

31.5 Disposal of dead animals

 

a) When animals die on farm disposal of the carcass and cleaning of the premises should be carried out in a manner that prevent any infectious or toxic health hazard to domestic or wild animals or man. The handling and disposition should preclude contamination of soils, air or water.

 

b) Rendering is a safe, rapid, convenient and economical method of disposition when this service is available and the situation permits. Renderers usually are required to use trucks, equipment and practices that prevent health hazards to animals and man.

 

c) When disposition on the farm is necessary, burying is the preferred method and should be used whenever feasible. In selecting a site it is well to consider the soil depth and the presence of underground cables, water or gas lines, septic tanks, water wells, etc.

 

 

d) Burning is difficult and expensive in labor and fuel. In selecting a site one should consider the proximity to buildings, stored materials, overhead cables, underground pipes, and prevailing winds that may carry smoke and odours. Burning requires that the carcass is placed on a combustible platform that may include oil, wood, coal, straw, tires, etc.   This method should be used only when burial is not feasible because of conditions such as high water table, excessive rock or for public health reasons.

 


 

 

32. PLANNING OF EPIZOOTIOLOGICAL MEASURES

=========================================

 

32.1 Introduction

 

a) All major animal population health/disease actions should be organized according to properly prepared programme. Its design represents the main formal instrument creating the framework for animal population health planning.

 

b) The knowledge of the animal population health  situation represents the basis  for  any  successful  animal  disease  prevention, control and eradication programme. Therefore,   the investigative  activities   should  be  target‑oriented  providing   the   necessary   information   on  health/disease conditions before starting,  during and at the end of the programme as well as during follow‑up period.

 

c) In general, several system tools have been developed for animal population health programme planning. The application of general principles must be always adjusted to the concrete case, situation and needs. The infinite variation of animal population health situation and influencing factors in space and time require different contents and forms in every specific programme.

 

d) Animal population health programmes may be started as pilot projects, for later extension to other areas. Preliminary pilot projects are useful for experimenting before starting the full projects. Feasibility study represents the other preparatory step.

 

e) The basis for any successful programme is the selection of correct strategy and methodology. It is recommendable to apply strategy and methodology which have already proved to be realistic, reliable and effective under comparable conditions.

 

f) General principles, selection of priorities, objectives of animal population health projects and objectives of disease control/eradication programmes see in chapter 23.

 

g) "Decision tree" and "critical path" methods are useful tools for planning.

 

32.2 Disease investigation planning

 

a) The  main objective of investigation of animal population health situation is epizootiological diagnosis which leads to  the analysis needed for any effective animal population health programme.

 

b) Disease investigation planning has to  have concrete objective to be achieved, clear‑cut target according to the needs for follow‑up action. Thus, it has to be meaningful,  useful and action‑oriented.

 

c) Disease  investigation objectives should identify what animals (species, categories) and disease(s) to be investigated, what methods to be used, what size of investigation (number or percentage of animals) and what places (territory, farms, sector, etc.), what timing (period, season, stage of epizootic process, etc.) of actions and deadlines.

 

   Among the criteria for the investigation range different indicators can be used such as  the relations between  the number of  animals to  be  investigated  and number  of  diseased, under direct or indirect risk, in foci etc.

 

d) Investigation according to its purpose and requirements should cover sufficient number of animals (all or of representative samples), size of territory and period. This is particularly true in cases of an intensive epizootic process with highly changeable situation and when investigating very dangerous infections.

 

e) Particular type of investigation programme is surveillance as continuing scrutiny of all aspects of occurrence and spread of a disease that are pertinent to effective control and to early warning system.

 

32.3  General principles of project design

 

32.3.1 Introduction

 

a) Individual countries usually have particular systems  for planning and management at different levels which should be respected.

     

b) Also for complex programme with many interacting factors,   a simplified, easily readable and straightforward project should  be presented  to decision makers and to all levels of programme execution.

 

c) The  core structure of the project consists of a hierarchy of basic project elements as follows:

 

‑ development objective

‑ immediate objectives

‑ outputs

‑ activities and

‑ inputs.

 

d) A project  should  be  developed  in  a  certain sequence. Namely, the inputs are to be transformed by respective activities into  specific  outputs,  which,  when  joined,  will lead to the accomplishment of the immediate objectives.  This will in turn to contribute at least in  part, to the achievement of the broader development objective. This is the basic theory and logic of the project design.

 

32.3.2 Preparatory phase, background and justification

 

a) Before starting  to write  the proper project,  there is a need for project context and  justification.

 

b) The reason for undertaking the project and why it is designed the way as  it  is  should  be explained.  It should describe the following:

 

  aa)  the problem to be  addressed by  the project, including the present  or  "pre‑project"  situation;  necessary  basic data on animal health (in zoonoses also  on human health),  on populations, socioeconomic consequences, disease   control, participating  services (institutions,  manpower, material supply, etc.), results of pilot programmes (if any), information on previous experience under similar conditions and other essential information;

 

  bb) the expected result - situation at the end of the project;

 

  cc) how and by whom the results of the project will be utilized ("target beneficiaries");

 

  dd) estimates of cost-benefit and effectiveness;

 

  ee) the particular strategy  and implementation arrangements of the project and why they  have  been chosen in  relation to other possible strategy or arrangement;

 

  ff) the reason for eventual external assistance;

 

  gg) special considerations, such as environmental issues, involvement of private sector, etc.;

 

  hh  arrangements  for  coordinating  this  project  with other efforts in the same sector, and

 

  ii) the capacity and  commitment of  the  Government or institutions to provide the inputs and support necessary for the project successful operation and to sustain the results at the end of the project.

 

c) Institutional  framework.  All contributing components in the national and/or local structures and their role must  be clearly identified. In addition,  institutions  outside  the  country  may  become an integral part of a comprehensive programme.

 

d) Project preamble may summarize  on one page the main elements of the programme, the phases for its implementation, budgetary consequences and the expected effect.

 

32.3.3  Development objectives

 

     The development objectives represent the  achievement of a broader development goal  at the sub-sectorial or sectorial levels to  which  the  project  should  contribute.  It  should  bear an explicit relationship to the objectives of the  country development programme. It represents a  higher  level goal (hierarchically directly above the immediate objectives)  for the achievement of which the project is a necessary means.

 

32.3.4  Immediate objectives

 

a) Properly defined immediate  objectives are the key to the project document.  The definitions of the other project elements and the structure of the project flow from these objectives.

 

b) Immediate  objectives  define what the project  itself is expected to  achieve.  It  should  be  defined  in  terms  of the specific change  in  status  or  condition  which the project  is  to  bring about. 

 

c) For either type  of project the  objectives must be realistic,  in  the  sense  that  they fall within the range of results which reasonably  may be  expected to be achieved within the limits of time,  money and human resources of the project.

 

d) They must also be stated in terms which  allow measurement or   at least observation  of their achievement during  and at the  end of the project.  Objectives in  terms  of  "improving", "strengthening", "supporting",  etc.,  are  difficult or impossible to  measure or observe. Therefore they should be avoided.

 

32.3.5  Outputs

 

a) The outputs are the building blocks which, when assembled, lead  to  the  achievement  of  one  or  more  of  the  immediate objectives.  They  are the tangible  "products"  that the project itself should produce to achieve its immediate objectives.

 

b) Outputs are to be described as concretely  as possible and in  verifiable  terms which permits a ready determination of whether and when they  have been produced and whether they are of the required quality.

 

c) Every immediate objective must be supported by at least one output. 

 

32.3.6  Activities

 

a) The  project activities  flow naturally  from the outputs. They consist of the substantive tasks to be carried out under the project life.  They must be goal ‑ oriented.

 

b) Each output must be supported by  at  least one activity. For  each activity should   also be indicated  where possible its expected duration, the proposed starting point during the project life,  whether  it  is  dependent  on  the  completion  of  other activities and who or which institution is responsible for carrying it out.

 

c) A work plan contains the timing of project activities and the parties responsible for then. A detailed work plan should be prepared by  the project management  at the  outset of project operations.

 

32.3.7  Inputs

 

a) The  inputs  such  as equipment,  supplies,  personnel,  fellowship,  etc.  are the "raw  materials"  of the project.  They are determined from an analysis of  the tasks which  need to be performed (activities) and their expected results (outputs).

 

b) All inputs required to carry out the  project's activities or to produce specified outputs are to  be  listed and justified.

 

c) The input list should indicate the type, quantity and quality of the input required. The description should be sufficient to  allow  judgement  of  the  appropriateness  to  the  project. Detailed  descriptions  of  inputs (in particular of the equipment) should  be  reserved  for the annexes.  They facilitate  procurement of major  items  of  technical  or  other  equipment.

 

d) Special attention  must  also  be  paid  to  the personnel component  to  assure  that  the most  appropriate  categories of personnel are utilized. Job descriptions (as annexes) are  important in  helping  to asses the optimum of project personnel and in speeding up eventual project personnel recruitment. Training  programme (as annex) should be included if  required  for  project with larger or complex training components.

 

32.3.8  Risks

 

a) It is possible for a  project in which  the major elements are  properly  defined which has  been  carefully implemented nevertheless to  fail.  This is because no project operates  in a vacuum   but  rather  in  an  oftentimes   difficult  development environment  in  which risks arise which may  seriously  delay or prevent the achievement of the project's outputs and objectives.

 

b) It  is  important that  these risks are  to  be explicitly addressed,  in the  first  instance  at  the  project formulation stage, and secondly during the project implementation.

 

32.3.9  Prior prerequisites

 

     The section of prerequisites describes those actions to be undertaken before carrying out project activities. These  can be of different  types  according to the concrete   case  (e.g. standardization of diagnostic methods including interpretation of the results, organization of in-service training, issuing legal documents related to the project activities  such  as  government  resolution, state  veterinary administration instructions, etc.).

 

32.3.10  Reviews, reporting and evaluation

 

a) The project should be subject to  regular review including additional ones which may be requested,  if necessary, during the project.  The review system as well as the project  reporting and evaluation forms and frequencies  should  be  established  by the project document.

 

b) Project  monitoring,  control and evaluation start  from  the time  when  the project actually  takes off. Monitoring  and   control  activities  carried  out enable  the necessary adjustments to be made during the project life.

 

c) The schedule of project reviews, reporting and evaluation annex is to be drawn up by project management at  the outset of project operations.

 

32.3.11  Project Budget

 

a) The budget must be accurately calculated and strictly aimed to  assure  the planned project  activities.  The contents, structure and format of the budget conforms to the norms established  by  the  government authorities eventually by the respective organizations, institutions or donors financially supporting the project.

 

b) The main structure usually consists of following components: personnel (professional, non‑professional and administrative support,  usually in  the form  of "man/months"), travel,  sub‑contracts (specifying types of  goods  or services), training (fellowship,  study  tours,  group  training, in‑service training, etc.), equipment (expendable, non‑expendable), premises and miscellaneous  (operation and maintenance  cost of equipment, reporting cost, sundries, etc.).

 

c) In case of radical methods requiring premature slaughtering of diseased or suspect animals a sum for eventual subsidizes to be included (if no adequate insurance system exists covering these cases).

 

d) Expected inflation rate must be applied  to get realistic budget.

 

32.3.12  Project organization and management

 

a) Lines  of communication,  supervision and  reporting,  as  well  as general coordination within the overall programme should  be described. A simple chart showing the institution framework with its essential lines of  programme execution is  most useful to  detect and deal with  gaps,  overlapping,  ambiguities,  hierarchical tangles and other discrepancies in the overall programme.

 

b) The framework for effective participation of staff in the project includes a description of the organization  of the work and lines of authority, which may be in the form of an organization chart. This facilitates the definition of a proper chain of command and reporting.

 

c) According to the size and character of the project current organization and management of the veterinary and services involved is used or a special temporal organization (unit or institution) is established.

 

32.4  Clearance and support of project

 

a) Every project should be cleared by respective decision making body before starting it. The clearance is usually based on official agreement of relevant political authority (e.g. national or local government), financing institutions and executing organization. The clearance signature should be made by the highest ranking plenipotentiary officers. The major national disease eradication projects should be based on government decision. Animal population health programmes cannot be the matter of veterinary services only !

 

b) Every control programme should have legislative support, according to administrative zone in which it will be performed. Local programmes, even pilot projects, should be supported by local authority enactments which should not be in contrast with the national legislation.

 

c) Cooperation agreements among the different interested authorities (e.g. agriculture, public health, environment) should be obtained to avoid overlapping and dissension. Steering committees or inter-sector executive committees can be useful form of coordination of different activities of cooperating institutions or sectors.

 

d) Cooperation must be secured also with the farmers (animal owners) and public, as well as with professional and political organizations. Their support can have decisive influence on the project implementation.

 

e) Different material and/or moral incentives (subsidizes, rewards for exemplary results, better prices for healthy animals and their products, etc.) supporting animal health projects proved to be useful in many cases.

 

f) When laboratory services are not an integral part of the programme, their collaboration must be secured.

 

g) In-service education and training concerning the programme, appropriate public education to assure community participation, intra and inter-service collaboration and coordination belong among other forms of project support.

 

h) It is obvious that financial support to cover all planned expenses has a key importance. To obtain necessary funding depends first on the quality of well justified project promising cost/effective results in priority fields of human and animal health development policy.

 

i) To get necessary support, first a consensus on the need and feasibility of the project among the professionals and then among the animal owners must be achieved to demonstrate its importance and priority grade to the decision-makers and public.

             

32.5 Disease emergency preparedness planning 

 

a) Early warning contingency planning. Early warning is the rapid detection of the introduction of, or sudden increase in, any disease of livestock which has the potential of developing to epizootic proportions and/or causing serious socio-economic consequences or public health concern. It embraces all initiative and is mainly based on disease surveillance, reporting and epizootiological analysis. These lead to improved awareness and knowledge the distribution and behaviour of disease outbreaks and infection, allow forecasting of the source and evolution of the disease outbreaks and the monitoring of the effectiveness of disease control campaigns.

 

b) Early reaction contingency planning. Early reaction is to carry out without delay the disease control activities needed to contain the outbreak and then to eliminate the infection in the shortest possible time frame and in the most cost/effective way, or at least to return to the status quo that existed previously and to provide objective, scientific evidence that one of these objectives has been achieved.

 

c) Planning against foot-and-mouth disease. From the exotic animal diseases the foot-and-mouth disease (FMD) is considered as the most dangerous one threatening any country. For immediate response to the FMD or other exotic disease suspicion must be prepared at all managerial levels thorough anti-epizootic emergency plans. To have everything needed ready in advance and not to waste time in the emergency, at all managerial levels (i.e. national, provincial, district, municipal and large livestock units) there must be elaborated “anti-FMD emergency plans” assured by staff, material and budget, regularly updated and usually verified through simulation exercises.

 

d) Among the main components of emergency plans belong:  very detailed procedures of clinical and epizootiological investigations, elaborated texts of intrafocal, perifocal and protective zones’ measures; pre-printed information texts, texts of public notices (quarantine orders), different questionnaires and forms to be filled (for specimen shipment to laboratory, for registration of and reporting on emergency disease situation, for vaccine provision order, etc.); lists of addresses and telephones of: veterinary service responsible officers and exotic disease emergency specialists (in the districts also of all veterinarians),  members of anti-epizootic committee, Reference Laboratories, Chief Veterinary Officer, Chief Epizootiologist, facilities of local up to national importance (e.g. slaughterhouses, rendering plants, sources of and stores with material needed for anti-exotic disease actions); list of villages and large ranches with the numbers of animals according to their species and categories;  local and territorial maps, etc.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

33. ORGANIZATION OF EPIZOOTIOLOGICAL ACTIVITIES

===============================================

 

 

33.1 Introduction

 

a) Good organization is the first precondition for any successful application of animal population health strategy, programmes and measures. Organization should accommodate the epizootiological objectives, programmes and activities in a given country, territory or sector.

 

b) Epizootiological organization is a very important component of any state veterinary service which represents an integrated part of government organizational systems. Official animal health service is principal institution performing and orienting epizootiological activities.

 

c) Epizootiological organization should be flexible, so that it can adapt, if required, to changes in animal population disease situations and conditions. It should create necessary conditions for applying disease control measures being ready for action at all times and at any place.

 

33.2 Structure of epizootiological organization

 

a) The structure of the organization of epizootiological activities within the structure of animal health services usually corresponds to the general administrative structure in the country concerned.

 

b) The central animal health service administration, under the direction of the national Chief Veterinary Officer (CVO), is responsible for technical activities in the country carried out by government veterinary officers. It is usually responsible for technical supervision of state, private and cooperative enterprises, in the areas of animal disease control, human health protection and animal production. It generally has overall responsibility for national veterinary institutes, such as central diagnostic laboratories, vaccine production and control laboratories, national research and training institutes and central storage, and for local-level institutions.

 

c) The majority of official veterinary service responsibility is in the field of epizootiology, i.e. animal population health protection and recovery and human health protection against diseases from animals. Therefore, within the service structure a particular network of veterinary specialists - epizootiologists (veterinary epidemiologists) should be established at all managerial levels.

 

d) In some countries particular veterinary public health units as components of public health activities participate in protecting human health against diseases from animals.

 

e) The most important tier of the animal health service is the field animal health service, which is in direct contact with producers, animals and their products. The work done at the village, farm, herd/flock and individual animal levels is decisive for any animal health programme.

 

f) Private veterinarians may be engaged in certain official duties. In the exercise of such duties they should be subject to civil service discipline under the authority of the respective officer of state veterinary service. Private veterinarians having daily contact with animals have important role in detecting primary outbreaks and application of preventive and provisional control measures.

 

g) Centralized organization with vertical operation offers better conditions for national prevention, control and eradication programmes and for protection of the livestock population. It also creates better conditions for the uniformity and coordination of diagnostic methods and control measures as well as mobilization in emergency cases.

 

h) Decentralized organization with horizontal operation offers better management conditions for identifying and solving local problems. This type of organization creates conditions for closer cooperation with farmers, meat industry, suppliers and consumers.

 

i) The strengths of both systems if combined to form mixed organization of animal health services is more likely to deliver effective services at both the local and national levels.

 

j) Intra and inter-service collaboration and coordination is necessary.

 

k) The organizational charter, inventory and budget of the official veterinary service should indicate its structure and the functions and responsibilities of each unit and should specify the facilities, resources and manpower assigned to its various sections, in accordance with functions exercised.

 

33.3 Manpower, facilities and funds

 

a) Manpower, standing and mobile facilities, means of transportation and communication and expendable resources of the official veterinary service should be adequate, as related to number and economic value of the livestock and commodities concerned, so as to ensure the effective implementation of official functions, including field, laboratory, meat inspection and quarantine operations.

 

b) Animal health personnel planning, education and training is of the utmost importance to any animal health service and to any animal population health programme.

 

c) Education, for the veterinarian in public or private practice, the livestock owner and the public in general is an essential component of disease control programmes. In-service training concerning animal health activities and programmes, appropriate public education (extension activities) to assure community participation belong among other forms of the support.

 

d) The facilities such as  veterinary laboratories for diagnosis, standard control and production purposes, research institutions, quarantine stations as well as other veterinary establishment should be located, staffed, equipped, provided with expendable resources, and operated, as consistent with effective implementation of the function assigned to them by relevant laws, rules and regulations.

 

e) There should be adequate financial and regulatory provisions to meet the specific flexible budget requirements as related to outbreaks of notifiable diseases, in order to ensure the immediate availability of means required for undelayed and full implementation of the epizootiological actions, as specified by relevant rules and regulations, applied to every such outbreak.

 

f) The government may draw up a policy under which some vaccines are issued free, e.g. those for the major epizootic diseases, while charges are made for the others.

 

g) It is essential that appropriate compensation is paid when animals are compulsory slaughtered for disease control purposes and that farmers are aware of this, otherwise they have strong disincentive to report unusual animal health events. Voluntary insurance schemes are helpful in covering the losses due to diseases.

 

h) Strong convincing arguments are needed to get financial funding priority in competition with many other important fields and sectors of national development policy being always limited by economic resources. 

 

33.4 Epizootiological legislation

 

a) The official veterinary services should have legal powers to exercise inspection over:

 

- animals, including domestic animals of all species, and wildlife at least as far as they may carry diseases transmissible to domestic animals;

- animal products;

- products destined for animal feeding;

- product destined for the prevention, diagnosis or treatment of animal diseases;

- any matter capable of transmitting animal disease;

- related premises, equipment, facilities and means of transportation;

- related documents.

 

b) In particular, the official veterinary service should have legal power to:

 

- perform epizootiological investigation of any area, clinical examinations of any animal and organoleptic or other technical examination of any product subject to official veterinary inspection;

- apply official identifying marks to animals, products, containers, premises, equipment and means of transportation;

- issue or withdraw official certificates and licenses;

- prohibit, limit, restrict or regulate import, export and movement within the country, of animals, animal products and other products subject to veterinary inspection, such as hay, straw and litter, as well as feed, vaccines and drugs;

- order and implement the isolation, sequestration and official observation of animals;

- perform or order to have performed diagnostic tests, vaccination and prophylactic or therapeutic treatment of animals, processing of products and disinfection of premises, equipment, facilities and means of transportation;

- collect samples for the purposes of diagnosis, sanitary or quality control, or legal evidence, and submit such samples to laboratory examination;

- confiscate animals and products, or cause such confiscation to be effected;

- destroy animals and products, or cause such destruction to be effected;

- register specified establishment and persons exercising specified activities;

- prohibit, limit, restrict or regulate the access of persons to specific premises or defined places;

- prohibit, limit, restrict or regulate the introduction to, or removal from specified premises of defined places, of animals, products and other objects;

- supervise the management of specified establishment;

- control and supervise the artificial and natural reproduction of animals;

- operate veterinary laboratories, quarantine stations and other specified official establishment under direct responsibility and authority of veterinary officers.

 

c) Any person being in the possession of an animal or carcass thereof which he suspects, or reasonably ought to suspect, of being affected with a notifiable disease, should be bound by effectively enforced law to give notice of such fact to the official veterinary service.

 

d) Epizootiological legislation should be supported with national standard definitions and norms complying with international norms to facilitate comparison and communication between the countries.

 

33.5 International cooperation

 

a) International cooperation is important prerequisite for successful epizootiological activities. The cooperation is based either on the bilateral or multilateral agreements or on operational contacts between veterinary services of neighbouring countries.

 

b) International organizations involved in epizootiological activities, coordination of control programmes and assisting to member countries are established on regional, continental and global levels.

 

c) There are three global international organizations dealing with animal population health:

 

aa) Food and Agriculture Organization of the United Nations (FAO) with the Hqs in Rome responsible for agriculture development and food production. Within the Animal Production and Health Division of the Agriculture Department is included the Animal Health Service. Its main role is to assist member countries in control of animal diseases and in development of vaccine production, diagnostic activities, veterinary education and training, organization of veterinary services.

 

bb) World Health Organization (WHO) with the Hqs in Geneva responsible human health policy in the world. Within the Communicable Diseases Division is included Veterinary Public Health Unit. Its main role is to assist member countries in the control of zoonoses.

 

cc) International Office of Epizootics (OIE) with the Hqs in Paris organizing intergovernmental cooperation in the field of animal diseases control, informatics, standardization, and export/import policy.

 

d) FAO and WHO as agencies of the United Nations have veterinary specialists also in regional offices for individual continents. 

 

 


 

 

34. RESULTS AND EFFICIENCY OF EPIZOOTIOLOGICAL PROGRAMMES

==============================================

 

34.1 Introduction

 

a) The results of the epizootiological programmes and measures can be evaluated as the difference between the situation achieved thanks to these activities and the situation at the beginning.

 

b) The results should be also evaluated comparing them with the objectives established at the beginning of the epizootiological programmes (see chapters 23 and 32).

 

c) Positive results in form of creation, maintenance and improvement of animal population health can be projected in biological, economical, public health and/or social fields.

 

c) The results and their characteristics are analogical as the beneficial consequences of collective animal health described in chapter 17.

 

d) Evaluation of the efficiency of epizootiological activities consists in the comparison of the achieved benefit with the inputs.

 

   On one side are the costs (extra cost incurred, revenue foregone) and on other side are the benefits (costs saved, revenue gained). In the analysis of disease control programmes, the extra costs of the programme are compared to the benefits of a reduction in the direct and indirect losses due to a disease plus the costs saved as the result of the change in the epizootiological situation.

 

e) In many cases of animal health programmes the results achieved can be the effect of not only of epizootiological activities but also of other contributions such as improvement of livestock husbandry management. Therefore, this fact should be taken into consideration.

 

34.2 Characteristics of programmes and measures results

 

  The results of epizootiological programmes and measures can be evaluated according to different criteria such as:

 

- animal species and categories

- causal factors

- environmental factors

- features of collective animal health

- features of animal population morbidity

- quantitative aspects

- qualitative aspects

- direct effects (immediate)

- indirect effects (secondary)

- space factors

- time factors

- visibility

- measurability, etc.

 

34.3 Biological results

 

a) Biological results of epizootiological programmes and measures represent the principal basis for economic, public health and social results.

 

b) Biological results can have different forms:

 

- collective animal health created

- animal population health protected

- animal population health improved (healthy animals rate increased, morbidity decreased or eliminated, mortality decreased or eliminated, etc.)

- epizootiological situation improved (nidality decreased, disease exposition/risk decreased, etc.)

- biocenosis improved, etc.

 

34.4 Economic results

 

a) Economic results of epizootiological programmes and measures can be subdivided in those where biological results are directly projected in economic ones (e.g. improved animal reproduction) and those where the economic results are derived indirectly (e.g. improved trade conditions).

 

b) Economic results can have different forms:

 

- number of animals and population structure improved

- animal population genetic value improved

- animal population development improved

- animal population reproduction improved

- animal population production improved

- animal products quality improved

- animal production process improved

- animal production efficiency increased

- animal products wholesomeness improved

- non-producing animals utility improved

- national economy positively influenced

- trade of animals and their products facilitated

- cost of veterinary services/measures reduced, etc.

 

34.5 Public health results

 

a) Public health results of epizootiological programmes and measures are reflected in the maintenance of human population free of diseases transmissible from animals, in reduction and elimination of human morbidity caused by these diseases and in improving epidemiological situation.

 

b) Public health results can have different forms:

 

- human population health protected against zoonoses

- human population health improved (zoonoses morbidity decreased, zoonoses mortality decreased or terminated, invalidity due to zoonoses decreased or terminated, etc.)

- human population specific zoonosis incidence terminated

- epidemiological situation improved (zoonoses nidality decreased, zoonoses exposition/risk decreased, etc.)

- cost of zoonoses treatment of humans reduced, etc.

 

34.6 Social results

 

  Social results of epizootiological programmes and measures are based on biological, economic and public health results. They are projected in the maintenance of good and improvement of worse human population living, cultural and political conditions. Increased income of the producers due to epizootiological activity results influences the possibility to improve their life. Increased food production is the best means against human population hunger and subnutrition.

 

34.7 Epizootiological programmes efficiency

 

34.7.1 Principles

 

a) The efficiency of epizootiological programmes and measures is based on the comparison (difference and relation) of the result benefit with the inputs (manpower, material, costs, time, etc.).

 

b) The programmes and measures are understood as effective if the value of the benefit is major than the inputs. There is a general tendency to achieve maximal possible benefits with minimal possible inputs.

 

c) Usually, the efficiency of epizootiological programmes and measures manifests not immediately but delayed after the inputs application (e.g. in control programmes economic results can be delayed for years). In the first phase the benefit can be zero, however, it manifests later increasing and accumulating during next periods to come. This fact creates difficulties in getting support due to the tendency to get input return as soon as possible.

 

d) The task of epizootiology is to identify the most adequate methods and ways for the solution of concrete animal population health problems with the maximal possible biological, economic, public health and social effect.

 

34.7.2 Analysis of the efficiency

 

a) Analysis of the efficiency should be oriented to its objectives. This type of analysis should complement epizootiological analysis for the evaluation of animal health programmes results.

 

b) The analysis should respect the factors of space and time, variability and complexity of epizootiological phenomena, relativity of the values, etc. avoiding super- and under-estimation.

 

c) Calculated efficiency should be logical not only from economic point of view but also epizootiological point of view.

 

d) The efficiency can be analyzed from different social aspects:

 

- national, regional or local levels

- interest of state, cooperative or private sectors

- interest of the producers or of the consumers

- interest of community or of the individuals

 

  Therefore the same epizootiological results can be evaluated differently according to the view applied. Not always what is beneficial to the community not necessarily is beneficial to the individual owner whose animals must have been killed due to strict epizootiological measures applied in the interest of the others. This facts demonstrates the relativity of the results of this types of analyses.

 

e) The evaluation of preventive measures efficiency is very complex and not easy due to the fact that it should be expressed the value of the benefit of animal population health protection based on what has been avoided. In this case the total value of protected population and its products should be taken into account.

 

f) Efficiency analysis of epizootiological programmes should be based on the comparison between the situation achieved by this activities and supposed situation if no programme applied.

 

34.7.3 Calculation of the efficiency

 

a) Efficiency is the effect or end-result achieved in relation to the effort expended in terms of money, resources and time. It is the extent to which the resources used to provide specific intervention, procedure, regimen or service of known efficacy and effectiveness are minimized.

 

   Efficacy is the extent to which a specific intervention, procedure, regimen or service produces a beneficial result under ideal conditions.

 

   Effectiveness is the extent to which a specific intervention, procedure, regimen or service, when deployed in the field, does what is intended to do for a define population. Among effectiveness indicators belong: prophylactic measures effect among animals at risk, recovery rate of treated diseased animals, etc.

 

b) Calculating the efficiency of epizootiological activities monetary units are usually used. They facilitate relative comparison of different economic phenomena values in different places (countries) and times. However, monetary units cannot express the majority of biological, public health and social phenomena values.

 

   Using monetary values following aspects should be considered: variability of national and international currencies, variability of prices in place and time, inflation rates, discount rates, seasonal prices, production prices, trade prices, taxes, fixed costs, variable costs, time horizons, etc.

 

  Discounting is not applicable on the life and health values (e.g. zoonosis eradication benefit continues in accumulated values).

 

c) Non-economic values should be evaluated using biological, public health and/or social measure units if any available. For example, the value of human life and welfare, protection of environment, etc. cannot be expressed in monetary values.

 

d) Often a combination of economic and non-economic measure units are used to evaluate on one side the cost of programme and on the other side the benefit of improved health.

 

e) For the evaluation of the efficiency can be used data based on measuring concrete situation (the best but the most expensive), or application of available norms (averages) or simple estimates.

 

f) Benefit of programme (BP) expresses the difference between the values of indicators characterizing the situation achieved by the programme (PROG) and the values of the same indicators without applying the programme (NOPROG). BP=PROG-NOPROG.

 

g) Generally, the comparison of the values of selected indicators at the beginning and at the end of the programme should be used (e.g. evaluation of the reduction of losses due to morbidity, of the benefit of the increase of "salubrity", etc.).

 

h) Simple absolute efficiency (EF) expresses the difference of value of benefit due to the programme (BEN) and the cost of inputs of the programme (COST). EF=BEN-COST.

 

   Each intervention has costs associated with it.  For   each intervention there is thus the question of whether the     benefits outweigh the costs. If the value of benefit is greater than the value of cost of inputs then the programme is justified and effective.

 

   Example: Simple absolute efficiency of bovine tuberculosis elimination programme in former  Czechoslovakia implemented in the period 1959-1968 and monitored up to 1978 was 7380 millions of crowns (benefit=95500 millions, cost=2170 millions).

 

i) Relative efficiency is measured using the indicator benefit/cost ratio (B/C) which expresses the relation of the value of benefit due to the programme (BEN) to the value of the cost of inputs of the programme (COST). B/C=BEN/COST.

 

   Example: Benefit/cost ratio of bovine tbc elimination programme in former Czechoslovakia implemented in the period 1959-1968 and monitored up to 1978 was 4.4 : 1).

 

   This indicator can be utilized also combining monetary and non-monetary values (e.g. biological benefit/cost ratio, public health benefit/cost ratio). In this case the indicator is called as efficiency/cost ratio. Efficiency/cost analysis can be done even when the monetary value of the benefit is not known.

 

   Examples: Suppose that the major motivation for brucellosis  control is to protect the public health and the monetary benefit  of that result can not be calculated because no one could decide what a human life is worth.   Efficiency/cost ratio of bovine tuberculosis elimination programme in former Czechoslovakia:  for 1 crown could be reduced the prevalence in average by 0.00046 heads of tuberculosis cattle. 

 

j) Relative efficiency can be measured also using the indicator cost/benefit ratio (C/B) which expresses the relation of the value of the cost of inputs of the programme (COST) to the value of benefit due to the programme (BEN). C/B=COST/BEN.

 

   Example: Cost/benefit ratio of bovine tuberculosis elimination programme in former  Czechoslovakia implemented in the period 1959-1968 and monitored up to 1978 was 0.23 : 1).

 

   This indicator can be utilized also combining monetary and non-monetary values. In this case the indicator is called as cost/efficiency ratio.

 

   Example: Cost/efficiency ratio of bovine tuberculosis elimination programme in former  Czechoslovakia:  to reduce the prevalence by 1 head of tb cattle cost in average 2190 crowns.  

--------------------------------------------

k) There are different other methods for the cost/benefit analyses in epizootiology (see EPIZOO software mentioned in the Preface). More information  in veterinary economics texts.

 


 

 

                B I B L I O G R A P H Y

 

1.  Acha P., Szyfres B. (1980) - Zoonoses and communicable diseases common to man and animals. Pan American Health Organization Sci. Publ. No. 345, Washington, 720 pp.

 

2.  Cannon R.M., Roe R.T. (1982) - Livestock disease surveys: A field manual for veterinarians. Australian Government Publishing Service, Canberra, 35 pp.   

 

3.  Halpin B. (1978) - Patterns of Animal Disease. The English Language Book Society and Bailliere & Tindall. London. 184 pp.

 

4.  Kouba V., Drazan J., Vrtiak J.O. (1971) - Vseobecna epizootologie. (General Epizootiology). Statni zemedelske nakladatelstvi, Praha, 587 pp.

 

5.  Kouba V., Truszczynski M. (1984) -  Manual of Epizootiology and Animal Health Ecocnomics. FAO Training Course on Epizootiology and Animal Health Economics, Hanoi, Vietnam, 250 pp.

 

6.  Kouba V. (1987) - Epizootiologia general. Secunda edicion. Editorial Pueblo y Educacion. La Habana, 867 pp.

 

7.  Kouba V. (1992) - Veterinary public health in world-wide animal health and production. Rev.Sci.tech.Off.int.Epiz., Paris, Vol. 11 (1), 241-254.

 

8.  Kouba V. (1994) - EPIZOO: a computer software package of methods for animal population health analysis and programming. Rev.Sci.tech.Off.int.Epiz., Paris, Vol. 13 (3), 637-650.

 

9.  Kouba V. (1994) – General Epizootiology. University of Veterinary Sciences, Kosice, 209 pp.

 

10.  Kouba V. (1995) – EPIZOO: software for veterinary epidemiology training and problem solving. Bull. World. Health Organ., 73 (1): 77-83

 

11.  Martin S.W., Meek A.H., Willeberg P. (1987) - Veterinary Epidemiology. Principles and Methods. Iowa State University Press / Ames, 345 pp.

 

12.  OIE (2006) - International Animal Health Code, Paris

 

13.  Putt S.N.H., Shaw A.P.M., Woods A.J., Tyler L., James A.D. (1987) - Veterinary Epidemiology and Economics in Africa. A manual for use in design and appraisal of livestock health policy. International Livestock Centre for Africa, Addis Ababa, ILCA Manual No 3., 129 pp.

 

14.  Schwabe C.W., Riemann H.P., Franti C.E. (1977) - Epidemiology in Veterinary Practice. Lea and Febiger, Philadelphia, 303 pp.

 

15.  Thrusfield M. (1995) - Veterinary Epidemiology. 2nd edn. Blackwell Science, Oxford.

 

16. Toma et al. (1999) – Dictionary of Veterinary Epidemiology. Iowa State University Press, Ames, 284 pp.

 

17. Col. (1995) – Manual for teaching basic veterinary epidemiology. IZSAM Teramo, WHO and FAO, 327 pp.

 

 

 


 

 

                                                              A N N E X : SELECTED EPIZOOTIOLOGICAL INDICATORS 

 

 

 

 

1. ANIMAL POPULATION HEALTH INDICATORS

 

 

Point prevalence rate of healthy animals        

                                               Ptsa  = ast/at

Period prevalence rate of healthy animals

                                               Ppsa  = asp/ap

Average prevalence rate of healthy animals       _    __ _

                                               Psa  = as/a

 

Incidence rate of healthy animals to existing total

                                               Isap  = asn/ap 

Incidence rate of healthy animals to average total

                                                 _        _

                                               Isa  = asn/a

Incidence rate of healthy animals to initial total

                                               Isao  = asn/ao

 

Extinction rate of healthy animals to existing total

                                              EXsap  = asex/ap

Extinction rate of healthy animals to average total

                                                 _         _

                                              EXsa  = asex/a

Extinction rate of healthy animals to initial total

                                              EXsao  = asex/ao

 

 

Animal population viability index

                                           N/MT  = an/(ad+ak)

Animal population natality rate

                                              N  = an/a

Animal population fertility rate

                                              F  = an/am

Animal population survival rate

                                             VI  = avi/ao

Animal population survival-to-weaning rate

                                              N' = a'n/an

Breeding animals survival rate

                                              B  = abvi/abo

Fattening animals survival rate

                                              A  = aavi/aao

 

 

 

 

 

 

 

 

2. ANIMAL POPULATION MORBIDITY INDICATORS                                                                                   Point prevalence rate of diseased animals

                                              Ptia = ait/at

Period prevalence rate of diseased animals

                                              Ppia = aip/ap

Average prevalence rate of diseased animals

                                                 _   __ _

                                               Pia = ai/a

 

Incidence rate of diseased animals to existing total

                                               Iiap = ain/ap  

 

Incidence rate of diseased animals to average total

                                                 _       _

                                               Iia = ain/a

Incidence rate of diseased animals to initial total

                                               Iiao = ain/ao

 

Extinction rate of diseased animals to existing total

                                              EXiap = aiex/ap

Extinction rate of diseased animals to average total

                                                 _        _

                                              EXia = aiex/a

Extinction rate of diseased animals to initial total

                                              EXiao = aiex/ao

                                                             

 

                                                              3. ANIMAL POPULATION MORTALITY                                 

 

Animal population mortality rate to existing total

                                                  MTo = amt/ap

Animal population mortality rate to average total

                                                   __       _

                                                   MT = amt/a

Animal population mortality rate to initial total

                                                   MTo = amt/ao

 

Animal population natural mortality rate to existing total

                                                  Dp   = ad/ap

Animal population natural mortality rate to average total

                                                   _        _

                                                   D   = ad/a

Animal population natural mortality rate to initial total

                                                   Do   = ad/ao

Animal population case fatality (lethality) rate

                                                   L  = aid/ai

 

Slaughtered animals rate to existing total

                                                   Kp   = ak/ap

Slaughtered animals rate to average total         _          _

                                                  K     = ak/a

Slaughtered animals rate to initial total

                                                  Ko    = ak/ao

 

 

4. INDICATORS OF EPIZOOTIOLOGICAL RISK

 

 

Grade of relative epizootiological risk

                                GRER = (aiexp/aexp)/(ainexp/anexp)

 

Grade of attributable epizootiological risk

                                GAER = (aiexp/aexp)-(ainexp/anexp)

 

Proportion of attributable epizootiological risk

                   PAER = ((aiexp/aexp)-(ainexp/anexp))/(aiexp/aexp)

 

Grade of superiority of epizootiological risk (odds ratio)

                              GSER = (aiexp/asexp)/(ainexp/asnexp)

 

Grade of individual risk of exposed animals

                                              GIRE = aiexp/aexp

 

Grade of individual risk of non-exposed animals

                                             GIRN = ainexp/anexp

    

 

 

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Note: All above indicators are included in EPIZOO software available free of charge in http://vaclavkouba.byl.cz.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

      SYMBOLS USED IN SELECTED EPIZOOTIOLOGICAL INDICATORS

      ====================================================

 

   Basic symbols        N a m e s

   ----------------------------------------------------------

 

   a               number of animals of given species

 

   as              number of healthy animals

 

   ai              number of diseased animals

 

   aid             number of dead diseased animals

 

   am              number of females in reproductive age

 

   an              number of new born animals

 

   an'             number of weaned animals

 

   ab              number of bred animals

 

   aa              number of fattened animals

 

   amt             number of total dead animals

 

   ad              number of naturally dead animals

 

   ak              number of slaughtered animals

 

 

 

   Small symbols        N a m e s

   ----------------------------------------------------------

 

   t               moment, existing at a given moment

                 

   -               average (average) during a given period

 

   p               period, existing during a given period

 

   o               initial moment, existing at beginning

 

   n               new (newly) during a given period

 

   ex              extinct during a given period

 

   vi              survived 

  

   exp             exposed

 

   nexp            non-exposed