AFRICAN SWINE FEVER IN MADAGASCAR: EPIDEMIOLOGICAL

AFRICAN SWINE FEVER IN MADAGASCAR:
EPIDEMIOLOGICAL ASSESSMENT OF THE RECENT EPIZOOTIC
Roger F1, Crucière C2, Randriamahefa N3, Zeller H4, Uilenberg G5, Randriamparany
T4, Gonzague M2, Rousset D4, Benkirane A6, Diallo A1.
1
CIRAD-EMVT, Animal health Program, BP 5035, Montpellier, France, 34032
AFSSA-Alfort - Unité de Virologie, BP 67, Maisons-Alfort, France F-94703
3
Ministère de l'Elevage, Direction Des Services Vétérinaires, BP 291, Antananarivo
Madagascar
4
Institut Pasteur de Madagascar, BP 1274, Antananarivo, Madagascar
5
A Surgente, route du Port, 20130 Cargèse (Corse), France
6
FAO, Animal Production and Health Division (AGA), Infectious Disease Group, Via
delle Terme di Caracalla, 00100, Rome, Italy
2
Since 1997, a highly contagious disease affects the swine population of
Madagascar. Initially described as an acute, febrile, and hemorrhagic disease and
designated as the Classical Swine Fever (CSF), a viral disease present in Madagascar
since 1965, the spread of this epizootic continued in spite of a vaccination campaign.
The field data collected in 1999 showed animal losses of higher than 60 %.
Pork is a significant element of the Malagasy culinary culture and improved
porcine breeding had developed over the last few years.
Material, Methods, and Results
In December 1998, samples were collected and dispatched to a reference
laboratory. ELISA antigen, isolation on cell cultures, experimental reproduction on
naive animals, Polymerase-Chain-Reaction (PCR), sequencing and serology made it
possible to diagnose, for the first time in Madagascar, the African Swine Fever
(ASF).
Data analyzed in 1999 showed an ELISA antigen rate of 14% (n=340) ; a PCR
rate of 62% (n=72) and a serological positivity rate of 4% (n=1042, Blocking-ELISA
test). It appeared that the virus was widespread: the major part of the Island was
contaminated.
The analyses of serums collected in 1996 and 1997 were all negative.
Proceedings of the 9th International Symposium on Veterinary Epidemiology and Economics, 2000
Available at www.sciquest.org.nz
The potential wild reservoirs of the ASF virus are existing in Madagascar. The
Bushpig, Potamochoerus larvatus, is located all over the lowlands. First viral and
serological investigations on the samples collected from Bushpigs do not show any
ASF positive results. The soft tick Ornithodoros porcinus domesticus (WALTON,
1962), previously identified in the western part of Madagascar, has been recently
discovered in various regions of the highlands.
Discussion
The hypothesis of the recent introduction of ASF was primarily supported by the
following data: (i) only acute and over-acute cases was recorded and outbreaks
extended throughout the country within a few months; (ii) the immunoenzymatic
assays of serum samples collected in 1996 and 1997 were negative; (iii) high
positivity rate in virology and low positivity rate in serology were recorded.
Preliminary genomes comparisons for the VP73 showed that: (i) the different
strains isolated in Madagascar during the epizootic, at different time and different
places, are quite identical, which is also in favor of a recent introduction and recent
diffusion of the virus; (ii) comparisons with several African strains (kindly provided
by the OVI in South-Africa and the LANADA in Côte d'Ivoire) showed that the
Malagasy strain is not particular but related to an austral African strain
("Mozambique 1994" strain).
In view of the available data, ASF could be considered as an emerging disease in
Madagascar. The occurrence and the extension of a new disease, so far considered as
"exotic" for Madagascar, confirm that a surveillance system is essential for the
protection of the livestock economic sector.
At the present time, because of its geographical proximity, ASF is threatening
Asia where pig breeding is highly developed.
The authors are grateful to the F.A.O. and the French Cooperation for their help
and assistance.
Proceedings of the 9th International Symposium on Veterinary Epidemiology and Economics, 2000
Available at www.sciquest.org.nz
Reference
1.
François Roger, Noéline Randriamahefa. La Peste Porcine Africaine à Madagascar : bilan
épidémiologique. Colloque scientifique : "les maladies porcines : impacts sur l'économie et la
santé". Académie Nationale Des Arts, Des Lettres Et Des Sciences. Antananarivo, Madagascar,
28-29 avril 1999.
2.
Harison Razanakolona, François Roger. Epidémiosurveillance de la Peste Porcine Africaine à
Madagascar. In Colloque scientifique : "les maladies porcines : impacts sur l'économie et la santé".
Académie Nationale Des Arts, Des Lettres Et Des Sciences. Antananarivo, Madagascar, 28-29
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africaine (PPA) à Madagascar: maladie émergente ou ancienne ?. 3ème Colloque du Réseau
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5.
S. Smondack, François Roger, Christian Burger, Noéline Randriamahefala, Catherine Crucière.
Isolation Of A Non-Hemadsorbing , Non-Cytopathic Strain Of African Swine Fever Virus In
Madagascar. Submitted for publication.
Proceedings of the 9th International Symposium on Veterinary Epidemiology and Economics, 2000
Available at www.sciquest.org.nz