Historia Medicinae Veterinariae, 2004, 29, 2 : 43-53
History of the screwworm (Cochliomyia hominivorax)
eradication in the Eastern Hemisphere
V. Kouba
Introduction
American screwworm, now
called New World Screwworm (NWS), caused
by Cochliomyia hominivorax (Coquerel)
belongs among dipteran flies and is distributed throughout the Western Hemisphere (Central and South
America and certain Caribbean Islands). This
horrible myiasis attacking warm-blooded animals and man spread in 1988, for the
first time in the history, outside of enzootic territories of American continent.
It was introduced through trade in North Africa, i.e. in the
Eastern
Hemisphere. This fly is an invader of fresh skin wounds
where they lay their eggs. The larvae hatch, crawl into the wound and borrow
into the flesh feeding on wounds fluids and live tissue. The wound can become
greatly enlarged due to multiple infestation and, if
left untreated, the victims die. The paper is based on historical documents of
the Food and Agriculture Organization of the United Nations (FAO), literature
sources (6,7,8,9) and personal experience. The first
FAO document on this subject was the Report of the FAO mission (15-22 April
1989), led by the author of this paper as the Chief, Animal Health Service
(responsible for United Nations animal health policy), sent
to investigate, confirm the presence of the NWS and identify limits of invaded territory
(4). Majority of the NWS documents were produced by the FAO Screwworm Emergency
Centre for North Africa (SECNA) as ad hoc
organization with special staff and financing to deal with NWS (3) established
by Dr E. Saouma, Director General, FAO on 15 June 1990. Among other sources
belong the protocols of the FAO
Screwworm Campaign Action Group, FAO/IFAD Screwworm Campaign Action
Group and FAO Animal Health Service Screwworm Task Force, all chaired by the
author (2,5). National statistical data on the results of epizootiological analyses, inspections
of animals and laboratory investigations were of particular importance.
Situation
First international
mission together with Libyan specialists carried out a fact-finding survey to
determine the reality of screwworm infestation. It was found the evidence that
the rapidly spreading myiases were prevalent in domestic livestock, mainly in
sheep, with the Tripoli area as the epicenter.
Entomological investigation by the mission reconfirmed the findings by local
specialists (1) that the causing agent was Cochliomyia
hominivorax. Maggots collected from animals were identified by the Faculty
of Veterinary Medicine and maggots from humans (e.g., from head, neck, hand and
scrotum wounds) by the Faculty of Medicine. Later control and eradication
programmes were supported by entomological investigations at Central Veterinary
Diagnostic Laboratory. Intensive follow-up national and international special diagnostic
programme, surveillance and reporting systems facilitated to identify screwworm
occurrence and to monitor territories at risk in Africa, Southern
Europe and Near East. Following
countries were identified as being at high risk: Tunisia, Algeria, Chad, Egypt, Niger and Sudan where FAO initiated
special programme of surveillance, monitoring and training. Extensive
surveillance and supporting communication activities were also undertaken in
other countries at risk: Burkina
Faso, Cameroon, Djibuti, Ethiopia, Mali, Mauritania, Morocco, Nigeria, Senegal and Somalia. Similar
surveillance was implemented in Spain, France, Italy, Greece, Turkey, Jordan and Israel. NWS invaded
during several months a territory of 25000 km2 between Mediterranean
Sea and parallel 32o10' (Sahara desert) and
between meridians 11o45' and 15o15' with more than 2.7 million
domestic animals. It was anticipated that without immediate control and eradication,
the fly would spread widely and cause incalculable losses in livestock
production and sanitary consequences. If the screwworm left uncontrolled, it
would inevitably spread to neighbouring countries and eventually into
sub-Sahara Africa, Mediterranean Europe
and the Near East.
Emergency
and containment programme
Immediately after the confirmation
of the NWS occurrence, FAO declared global emergency, started special
surveillance, preventive and control activities and began preparation for the
application of the sterile insect technique (STI). NWS was made notifiable to
be reported as other danger diseases of international importance. First control
phase consisted mainly in: establishing specific diagnostic system to detect
and monitor NWS in the North Africa region and other territories at risk and controlling
animal populations and their movement (individually examined for wounds and
screwworm larvae) to prevent introduction of NWS to territories free of the
pest. It was arranged for production of coumaphos (5%) powder for treatment of
wounds and prophylactic spraying (0.25%). Millions of sampling/treatment kits
which consisted of insecticide powder and larval collection tubes were routinely
provided to livestock owners. The fly's mobility made containment extremely
difficult. Adult flies can travel up to 200 km and, where conditions are favourable,
the size and range of the population can expand rapidly. The screwworm presence
in North
Africa, therefore, was a concern of international significance:
unless quickly eradicated, it would inevitably spread. It could easily migrate
around North- and West African coasts and down the Nile valley. Such
as infestation would be virtually impossible
to eradicate
and the countries affected would be saddled with the on-going expense of
treatment and control programmes and with enormous consequences. The only way
to prevent this devastating insect pest from spreading throughout the Eastern Hemisphere was by
immediate eradication ("now or never !").
Use of sterile insect technique (SIT).
SIT was developed by
R.C. Bushland and E.F. Knipling in 1938 and proved to be effective in USA and Mexico. Initial study
confirmed that North African strain of NWS was compatible with the strain used
for the production of sterile insect at Tuxtla
Gutierrez factory in Mexico (only in
world). The technology relied on the regular sequential release of factory bred
and sexually sterilized flies. The success of SIT depended on the ability of
the factory-reared sterile males to compete with wild males and mate with a
sufficient percentage of the wild female population to break the wild
pest's life cycle. The screwworm flies were reared artificially and exposed to
irradiation by caesium 137 shortly before they emerge from the pupae. Male
flies were sterile but able to mate. The female mates only once,
and when mated with a sterile male, lays eggs that do not hatch. Field application
of this method in North Africa required demanding
preparation and solving immense problems of biological, technological,
managerial, financial, social, legal, political and
language character. After not easy legislation process, on March 15, 1990, United
States President Bush signed law exceptionally permitting the sale of sterile
NWS produced under US and Mexican governments to be used in Libya. Sterile flies production capacity of the Mexican facility was
significantly increased to be able to meet additional requirements for
eradication
programme in North Africa. Necessary
support in terms of staff, funds, organization, management, equipment,
transport, facilities, logistic, communication, extension, etc. was ensured. SIT
was supported by NWS population suppression through animal inspection, wound
treatment and preventive spraying of herds/flocks at risk, efficient diagnosis,
recording and reporting of screwworm cases, communication campaigns and control
of animal movement.
It was necessary to
identify programme phases and key moments for STI application in time and
space. Scientifically based monitoring system and epizootiological analyses
were complemented by more detailed mapping, including use of satellites
photographs to identify ecological conditions and their dynamics for
corrections of STI targets and timing. During pilot phase it was necessary to
develop the infrastructure and test the feasibility of transferring the proven technology,
i.e. to test the logistic support necessary to apply SIT successfully in North Africa. New
laboratory facilities were established for identification of NWS and quality
control. The tests involved analyzing emergence, mortality, flight agility and
longevity and were conducted both in Libya and Mexico.
Initially, it was
necessary to study: sterile screwworm surviving in the best possible conditions
from the factory up to final dispersion and mating in target zones in a very distant
territory; transcontinental transport of sterile flies and their storing under
North African conditions up to reach the optimal stage for release and mating;
effective system of aerial dispersion of sterile flies in terms of frequency,
intervals, size and location paths; etc. It was established a continuous
control from production factory up to effectiveness of STI practical application
and continuous surveillance in invaded and threatened zones and countries. The
sterile NWS is a living insect requiring particular conditions with regard to
temperature, packaging, shipping, storage, handling and
must be
transported within a limited period. In order to ensure good quality flies, a
decision was taken to transport the insect in the pupal stage by packing 1600
pupae into small biodegradable cardboard dispersal boxes. Each box contained a
small cup of special gelled diet for the emerged flies. The temperature during
ground and aerial transportation of the pupae must remain at 10o C. Afterward, the sterile flies were stored in chambers at a
temperature of 25o C to 27o C for a minimum of 48 hours
until 80 % of the pupae emerged. Then the boxes were loaded on twin-engine
aircraft, each fitted with a specially designed chute through which the boxes
were released at a predetermined rate. The boxes were designed to open during
their fall from the aircraft, or on impact with the ground, thus releasing the
flies. Pilot dispersion started in December 1990 with more than 5 million of
sterile flies and continued in January 1991 into eradication phase without
interruption.
Eradication
phase
The main activity
consisted in intensive dispersion of sterile flies over infested area of about
25000 km2 and protective barrier of 15000 km2 including
2500 km2 in north-eastern Tunisia. From January to 15 October 1991 a total 1257
million sterile flies were dispersed. Usual weekly dispersion of 40 million
flies was carried out using five twins’ engine aircraft belonging to Libyan
Aeroclub. The dispersal aircraft flew along predetermined paths, 4 km apart,
and boxes were dispersed at a rate of 3 to 10 per minute as the plan flew at
240 km/hour at an altitude of 500 m. On each dispersal day an area of
approximately 6400 km2 was covered, with an average distribution of
800 flies per km2. An
extensive communication campaign ensured that people in the affected regions
were fully informed on the programme (using radio, TV, leaflets, posters,
etc.). The population was informed why low-flying airplanes were dropping
cardboxes full of flies
of American
origin over large territory. Because no further evidence of
NWS in the six months following detection of the last case in April 1991, SIT
was terminated. From July 1989 were reported 14111 cases. Tens of human cases were
reported as well. The continuous compilation of NWS negative results of surveillance
throughout the country confirmed the evidence that NWS no longer existed in North Africa. A resume of
data from field activities since beginning of May 1991, the first month with no
NWS detected, through to the end of the year showed that nearly 180000 trapped
females NWS flies were dissected, with no fertile flies found. The number of inspections
of animals exceeded 22 million, with 700 samples of other larvae collected from
wounds, but no NWS found. Almost 3/4 million animals were inspected at
quarantine stations, with the same results. Continuous surveillance in following
years has confirmed NWS eradication in North Africa and thus in
the whole Eastern Hemisphere
.
Management
and support
Effective
international technical and financial assistance together with strong national
public veterinary services were considered the crucial pre-requisites for the
success. The eradication was the outcome of the activities of many thousands of
specialists, managers, farmers, supporting staff to cover extremely complex
spectrum of all necessary tasks at local up to intercontinental levels.
Particular role had specialists with experience from screwworm eradication in USA and Mexico. The intercontinental
programme was supported, additionally to FAO, also by other United Nations
agencies: International Atomic Energy Agency (IAEA), United Nations Development
Programme (UNDP) and International Fund for Agriculture Development (IFAD).
Support was provided also by 22 international donors and financial
institutions. Local government provided a range of facilities, support staff
and other assistance to the project.
Department of Veterinary Service employed approximately 300
veterinarians and supporting staff of about 1200 persons. In total more than 50
million inspections were recorded (e.g., during eradication phase - every
months the surveillance units were carrying out about 3 million inspections and
treating nearly 20000 wounds). National authorities ensured also landing,
take-off, parking, servicing, refuelling and repair facilities for project aircraft;
facilities for storage and loading of boxed flies; support staff to assist with
and implement air dispersal.
FAO Animal Health
Service was in charge of the programme from the beginning up to June 1990;
particular responsibility had Service Chief V. Kouba (Czechoslovakia) and
Senior Officer R.E. Reichard (USA) assisted by B. Hursay (United
Kingdom). Afterward, SECNA
took over the
main responsibility. Its headquarters professional staff consisted from:
E.P.Cunningham, Director (Ireland), A.E.
Sidahmed, Senior Operation Officer (Sudan), M.
Vargas-Teran, Technical Officer (Mexico), S. Barnes,
Information Officer (Australia), M. Kassa,
Computer Data Management Officer (Ethiopia) and P.McCormick,
Media Liaison (United Kingdom). SECNA
field programme (directorate in Tripoli) was implemented by following
professional staff: D.A. Lindquist, Director (USA), M.Abusowa, Co-Director
(Libya); Epidemiologists R.E. Reichard (USA), M. Abu-diah (Libya), L. Sjoeland
(Sweden), H. Lame
(Netherlands), F.A. Pouldevigne (France) and A. Bengere (Libya); field working
specialists L.F. Liera (Mexico), A. Belazi (Libya), A.
Martinez (Mexico), M. Amara (Libya), J. Haloun
(Libya), L. Tunisi
(Libya), D. Bruzzone (Italy) and S.M. Toure (Senegal); laboratory specialists
R. Garcia (Mexico), K.
Mughadmi (Libya), J. Chirico
(Sweden) and M.Taher
(Jordan). SECNA
staff included also aviation, communication and information specialists, distribution
center and administrative workers.
Conclusion
The losses reached
hundreds of millions US$. In case of spreading over Sahara the consequences
would be irreparable and supposed future losses were estimated to be of many billions
of US$. Only costs of on-going treatment and control were estimated to be of
hundreds of millions US$. In addition to the economic impact, a continent-wide
infestation would pose a major human health risk. In remote areas where medical
facilities were limited or not existing at all, humans would fall easy victims
- particularly children, the sick and the aged. For Africa's wildlife
was the risk of significantly reducing natural populations and establishing a permanent
"breeding pool" from which it could re-infest domestic herds. The
eradication showed a clear economic return. Pre-eradication programme cost
about 10 million US$ and the eradication about 80 million US$. An independent
economic appraisal, considering also avoiding
future spreading,
showed a very high benefit/cost ratio - 50:1. Eradication without recurrence
was achieved in extremely short period before the parasite further spread and
become enzootic in the Mediterranean Basin and
eventually in other areas of the Eastern Hemisphere. Eradication itself took about six months,
although it was preceded by 1.5 year of preparation and followed by one year of
continuous surveillance and preventive actions. The hemisphere was saved from
this very dangerous zoonosis and could be again declared as NWS free territory.
The eradication of Cochliomyia
hominivorax in the Eastern Hemisphere was the most
successful large international animal health programme organized by the United
Nations.
Tab.
1
Screwworm cases by
months in North Africa during
1989-1992
(each
case = laboratory-confirmed infestation of one animal)
============================================================
Months 1989 1990 1991 1992
------------------------------------------------------------------------------------------
January ? 102 3 0
February ? 94 2 0
March ? 190
0 0
April ? 289
1 0
May ? 371
0 0
June ? 917 0 0
July 111
1 570
0 0
August 29 2 145 0 0
September 75
2 932 0 0
October 419 1 701 0 0
November 796
1566 0 0
December 607
191 0 0
-----------------------------------------------------------------------------------------
Total 2 037 12
068 6 0
===========================================================
References
1. El-Azazy O.: Wound myiasis caused by Cochliomyia hominivorax in Libya. The
Veterinary Record, 1989, 124. 103.
2. FAO/OIE/WHO Animal Health Yearbook
1990, 1991, 1992. FAO, Rome.
3. Food and Agriculture Organization of
the United Nations (FAO): The New World screwworm eradication programme: North
Africa 1988-1992. FAO, Rome, 1994, 192 pp.
4. Kouba V., Toure S.: Study on the
situation of the American Screwworm Fly (Cochliomyia
hominivorax). Report of the mission to Libyan Arab
Jamahiriya, FAO, Rome, 1989.
5. Kouba, V.: Information note on FAO
activities to combat screwworm in the Near East Region. 20th
FAO Regional Conference for the Near East, Tunisia, 1990.
6. Kouba V.: Screwworm (Cochliomyia hominivorax) and its
eradication in North
Africa
using sterile insect technique - Epizootiological analysis. Eradication
programme. Agricultura tropica et subtropica. Universitas
Agriculturae Praga, vol.34, 2001, 97-109.
7. Lindquist D., Abusowa M.: The New
World screwworm in North
Africa.
FAO Wld. Anim. Rev., Special Issue: October 1991, 2-7.
8. Reichard R.: Case studies of emergency
management of screwworm. Rev. sci. tech. Off.int.Epiz.,1999,18(1):
145-163.
9. Vargas-Teran M.: The New World
screwworm in Mexico and Central America. FAO Wld. Anim. Rev., Special
Issue: October
1991, 28-35.
Received July 2003
Address of the author:
Prof.MVDr V. Kouba, DrSc.,
Former Chief, Animal
Health Service, Food and Agriculture
Organization of the
United Nations
P.B. 516, 17000 Prague 7, Czech Republic