Controlling animal health risks: CIRAD-EMVT FAO Collaborating Centre on Epidemiology of Tropical Animal Health

Statement

Increased global trade, climate and ecological change, and new animal production practices have created an environment that favours the emergence and spread of infectious and parasite-borne diseases. In the tropics, the phenomenon has been exacerbated by inadequate animal health systems and a lack of information on certain epidemiological cycles. Epitrop, a group of researchers from various teams at CIRAD's Animal Production and Veterinary Medicine Department, was set up in 1998 to provide a more satisfactory response to requests from international organizations in terms of disease prevention and control. The epidemiological research being conducted at CIRAD is oriented towards monitoring, analysing and modelling the major tropical infectious and parasite-borne diseases: trypanosomiasis, contagious bovine pleuroneumonia, rinderpest, peste des petits ruminants, African swine fever, Rift Valley fever, bluetongue and others. The network is working with numerous scientific and technical organizations in both industrialized and developing countries. Its operations in 2003 concentrated on three diseases.

Bluetongue

Bluetongue surveillance has been stepped up in Corsica and in mainland France. Predictive models are currently being developed. Surveillance is based on entomological, serological and virological monitoring. Bluetongue is a viral disease, spread by midges of the genus Culicoides (Diptera: Ceratopogonidae), and more precisely by Culicoides imicola in the Mediterranean region. It is a major disease that can have serious economic consequences. Bluetongue has been considered an emerging disease in the Mediterranean since 1998, although serious outbreaks occurred on the Iberian peninsula in the 1950s and on several Mediterranean islands. After the epizootic in Corsica in 2000, the Food Products Division of the French Ministry of Agriculture set up a surveillance system with scientific and technical support from CIRAD, the French national reference laboratory for bluetongue, which, as such, works closely with AFSSA, the French food safety agency.

Predictive models are currently being developed in partnership with the UK Institute for Animal Health Pirbright Laboratory and the University of Oxford in the United Kingdom, using satellite data (vegetation indexes, temperature, etc.) and entomological data gathered from surveillance operations in Corsica and on the mainland. These models were validated using entomological data obtained by Culicoides spp. trapping operations in 2002. The correlation between predictions of the vector C. imicola and bluetongue foci actually recorded in Corsica validated the accuracy of the model used.

In addition, statistical models have been used to draw up a map predicting C. imicola abundance in the Mediterranean basin, and thus the risk of disease establishment or spread. The map shows large numbers of insects in many zones recently affected by bluetongue. It suggests that certain regions around the Mediterranean and several zones in southeastern and southwestern France will be at considerable risk in the near future. Global climate change has favoured the spread of zones propitious to the development of vector insects, which may be one of the reasons for the spread of the disease. These results show that it is vital to step up epidemiological surveillance operations in France and possibly elsewhere and pinpoint the priority zones of risk. This work has strengthened the relations between CIRAD and its European partners and should also, in the medium term, lead to new links with Mediterranean countries, particularly in the Maghreb region of North Africa.

Peste des petits ruminants and trypanosomoses

While monitoring rinderpest in wildlife under the Pan African Programme for the Control of Epizootics (PACE), CIRAD also tested for the presence of peste des petits ruminants (PPR). This programme is run by the African Union and largely funded by the European Union. PPR is spreading rapidly in the tropics and, as analyses of samples have shown, the multiplicity of hosts receptive to the virus among the local wildlife could prove to be a major obstacle in controlling the disease. It is therefore essential to establish its epidemiology, notably through molecular epidemiology and modelling studies.

The surveys were undertaken in Kenya, Ethiopia, Uganda, Democratic Republic of the Congo, Central African Republic, Benin and Chad. The Table shows evidence of the circulation of the PPR virus in West Africa while the only zone in East Africa showing positive animals was Kenya. The results of PPR serum virus neutralization tests (VNTs) have significantly higher titres than those of rinderpest VNTs. But, in the herds examined in Kenya, there was epidemiological and virological evidence that rinderpest infection was the cause of the antibody by cross-reactivity (R. Kock, PACE, personal communication). The survey results demonstrated that buffaloes are useful as sentinels for PPR also; they are already the top species for rinderpest serosurveillance.

Several years' work in conjunction with the International Centre for Animal Husbandry Development and Research in Subhumid Regions (CIRDES) has resulted in the development of targeted control methods against trypanosomoses that can be practised by animal farmers in developing countries. CIRAD is currently working with CIRDES on the epidemiology of trypanosomoses in West Africa, and particularly on the transmission of tsetse vectors, the mechanism involved, and the identification of zones in which the diseases are spreading. CIRAD is continuing to supplement its expertise in epidemiology. It is working to transfer tools and methods to partners in developing countries - evaluation of the efficacy of surveillance networks, risk analysis and management, emergency intervention capacity - and to develop new research topics - analytical and molecular epidemiology, spatial analysis and modelling. Since 2002, it has been looking at how to structure these operations so as to increase their efficiency and clarity.

Further information can be obtained from the Epidemiology and Health Environment Units, Animal Production and Veterinary Medicine Department, CIRAD-EMVT (Web site http://epitrop.cirad.fr; e-mail franç[email protected], [email protected] and [email protected]).

Bibliography

Roger, F., Tatem, A., De La Rocque, S., Hendrikx, P., Baylis, M., Delecolle, J.C. & Rogers, D. 2002. L'émergence de la bluetongue en Corse et dans le Bassin méditerranéen (1998-2002): modélisation des zones à risque à partir de données satellitaires. In Regards croisés sur les changements globaux. INRA, Cnes, Cnfcg, Insu. Arles, France, 25-29 November.

Libeau, G. & Caufour, P. 2002. PPR: an emerging disease in East Africa? A review of PPR in livestock and wildlife with a focus on differential diagnosis. In Training under the PACE epidemiology wildlife component workshop. Arusha, United Republic of Tanzania, 29 November - 3 December.