SCREWWORM (COCHLIOMYIA
HOMINIVORAX) AND ITS ERADICATION IN
KOUBA, V.
Abstract
The screwworm caused by Cochliomyia hominivorax,
attacking warm-blooded animals and man, was discovered for the first time in
the history, outside of American continent. After confirming the occurrence of
this horrible myiasis
in
Key words:
Cochliomyia hominivorax - screwworm - epizootiological analysis - myiasis -
surveillance - zoonosis
List of
abbreviations: FAO - Food and Agriculture Organization of the United Nations;
NWS - New World Screwworm (Cochliomyia
hominivorax); SECNA - FAO Screwworm Emergency Centre for
Introduction
New Word Screwworm (NWS), originally called
American screwworm,
spread outside of its natural environment on the American
continent for the first time in the history. This horrible myiasis, which was
discovered in
Material and methods
The paper is
based upon official documents (5), personal investigation (2), publications of specialists involved in North African campaign such
as Abusova (3), El-Azazy (1), Lindquist (3), Reichard (4) and Toure (2).
Epizootiological
analysis consisted in field investigations, laboratory testing, surveillance,
monitoring and data processing during NWS occurrence in
Initial data
were obtained by the first FAO mission sent to
After
introducing obligatory reporting of this myiasis epizootiological analysis
became more precise. NWS occurrence information came from systematic preventive
inspection of animals, quarantine stations, animal movement control, sampling
and laboratory investigation of all collected flies searching for NWS.
After starting
eradication programme epizootiological analyses were complemented by more
detailed mapping to identify and delimited myiasis territorial distribution and
by more data on dynamics, ecological conditions and other factors important for
identifying sterile insect technique targets, timing and intensity.
Key importance
for epizootiological analysis were documents of government animal health
service and of the SECNA as temporarily established organization to deal with
NWS at international level and operating in Libya.
Results
First mission
to
The mission
together with the Libyan specialists, carried out a
fact-finding survey to determine the reality of screwworm infestation. At
Veterinary Clinic in Hadba Al Khadra several larvae were collected from the
tail and from the breast of two diseased lambs. Immediate entomological
investigation in Central Veterinary Diagnostic Laboratory in
Next step was
to identify the limits of invaded territories.
The mission visited nine districts in and around
Deep wounds
including a great number of larvae were observed mainly on sheep (rams, ewes,
lambs) in various parts of the body (fatty tail, face, abdomen, anus, vagina,
navel, base of horn, mouth). Other animal species such as cows, calves, camels,
dogs, stallions, etc. were affected in various parts of the body. NWS cases
were treated by insecticides such as phosphorothiolate (Neocidol) and Dermatox.
However, extreme cases were followed by death, mainly in lambs.
Myiases cases
were reported also from
Following
countries were identified as being at high risk where FAO, as recommended by
its mission, initiated surveillance, monitoring and training:
The way of
introduction was suspected to be the import of sheep from infested American
continent. From
Reliable data
on NWS occurrence started after establishing obligatory reporting and
investigations of all collected larvae from wounds, i.e. from July 1989. That
year, additionally to previous ad hoc finding,
were laboratory-confirmed 2037 cases, in 1990 12068 cases (peak in September)
and in 1991 only 6 cases. (Tab.3).
Very intensive
surveillance programme was introduced. For example only in 1991, i.e. last year
of NWS occurrence, were carried out 30516633 preventive inspections of animals,
918136 animals were inspected in quarantines, 176936 male flies and 213939
female flies were captured for diagnostic purposes. The last case was in April
1991. During next 10 years of intensive follow-up surveillance no one new case
of NWS was detected confirming NWS free status in the East Hemisphere.
Particular
study by the USDA laboratory at Fargo, North Dacota, USA confirmed
compatibility of the North African strain with American strain (Costa Rica-91)
used for mass-rearing at the Mexican facility producing sterile flies. This was
key discovery for using sterile insect technique to eradicate this myiasis.
The losses
reached hundreds of million
Discussion
and conclusion
For the first
time in the history, this relentlessly destructive pest became established
outside its natural range in the Americas and, if left uncontrolled, it would
inevitably spread to neighbouring countries and eventually into sub-Sahara
Africa, the Near East and Mediterranean Europe.
Although the
infested area in
The author
presented to General Session of the International Office of Epizootic held in
Immense size
and complexity of scientifically based continuous monitoring system supported
by laboratory etiological investigations followed by immediate successful
actions at field and managerial levels, represented
one of the most effective surveillance in the history of animal health.
References
1.
El-Azazy O., 1989. Wound myiasis caused by Cochliomyia hominivorax in
2.
Kouba V., Toure S., 1989. Study on the situation of
the American Screwworm Fly (Cochliomyia
hominivorax). Report of the mission to Libyan Arab Jamahiriya, FAO,
3.
Lindquist D., Abusowa M., 1991. The
4.
Reichard R., 1999. Case studies of emergency
management of screwworm, Rev.sci.tech.Off.int.Epiz.,1999,18(1):
145-163.
5.
Food and Agriculture Organization of the United
Nations, 1994. The
Tab. 1
Screwworm territorial distribution in
by the first international fact-findings mission
in April 1989
=========================================================
District Distance
from
--------------------------------------------------------------------------------------
Zawia 50
km westward first in September 1988
last in January 1989
Sorman 80
km westward one suspected case
Zahra 40 km south-westw. cases
started in October
1988
Hadba Al
Khadra 5 km southward positive
cases
Ain Zahr 100 km south-eastw. positive
cases
Tajore 30
km eastward first case in July 1988
Garabuli 60
km eastward frequent from November
1988
Gasarkihar 75
km eastward cases from October 1988
Khomes 120
km eastward no cases
========================================================
Tab. 2
Main domestic mammals in African countries at
screwworm risk with special surveillance and measures (1000 heads), 1989, FAO
==============================================================
Country Cattle Sheep Goats Horses Total
-----------------------------------------------------------------------------------------------------------
At high risk:
Libya 238
5100
1100 22 6460
Tunisia 626
5935
1259 55 7875
Egypt 2771
3310
2407 18 8506
Algeria 1366 17301 2454 83
21204
Chad 4298
1926
2838 184 9246
Others at
risk:
Burkina Faso 3937 5048
6563 22
15570
Cameroon 4703
3407
3428 14
11552
Djibuti 188
433 502 - 1123
Ethiopia 29633 23320 17733
2650 73336
Mali 5007
6072 6072 72
17223
Mauritania 1350 5067 3400 17
9834
Morocco 3284
13528 5059 190
22061
Nigeria 13974
12477 23428
208
50087
Senegal 2616 3464 2528 419
9027
Somalia 4100
12783 17600 1
34484
-----------------------------------------------------------------------------------------------------------
Total 100883
143575 117602 4058
366118
==============================================================
Tab. 3
Screwworm cases by months in
(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 1, 937 12 068 6 0
=====================================================