Appendix 22 Molecular epidemiological studies of Foot-and-Mouth disease virus in sub-Saharan Africa indicate the presence of large numbers of topotypes: implications for local and international control Vosloo, W.1*, Dwarka, R.M.1, Bastos, A.D.S.2, Esterhuysen, J.J.1, Sahle, M.3, Sangare, O.4 1
Exotic Diseases Division, Onderstepoort Veterinary Institute, Private Bag X05, Onderstepoort, 0110, South Africa 2 Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa 3 National Animal Health Research Centre, Ethiopia 4 Laboratoire Central Veterinaire, BP 2295, Bamako, Mali Abstract: Six of the seven serotypes of foot and mouth disease (FMD) virus occur on the African continent and numerous topotypes occur for each serotype. Due to underreporting of FMD, the current strains circulating throughout sub-Saharan Africa are in most cases not known. For both SAT-1 and SAT-2 the genetic diversity is reflected in antigenic variation and indications are that vaccine strains may be needed for each topotype. This has serious implications for control using vaccines and for choice of strains to include in international vaccine banks. The epidemiology of FMD is further complicated by the presence of large numbers of persistently infected African buffalo (Syncerus caffer) and other wildlife species which together with largely uncontrolled movement of domestic animals may spread the disease over vast distances. This dearth of knowledge on FMD in Africa poses a serious threat to regions free of FMD in the face of increased international travel and the possible smuggling of illegal bushmeat and other livestock products. Introduction: Foot and mouth disease (FMD) virus probably originated from Africa since greater genetic variation occurs in the SAT types (Vosloo et al., 1995; Bastos et al., 2000; Bastos, 2001; Bastos et al., 2001; Bastos et al., 2003a and b) and a sub-clinical cycle occurs in African buffalo (Syncerus caffer) where the virus can persist in a single animal for up to five years (Condy et al., 1985). This is the only species for which long-term maintenance of FMD virus has been described (Hedger, 1972; Hedger et al., 1972; Hedger, 1976; Condy et al., 1985; Thomson, 1994; Thomson et al., 2001; Thomson et al., 2003). During persistent infection in buffalo, the SAT type viruses undergo high rates of mutation, giving rise to genetic and antigenic variants (Vosloo et al., 1996). The disease is endemic to most countries in sub-Saharan Africa (Vosloo et al., 2002) and will not be eradicated from southern and East Africa while infected buffalo are present. Disease-free areas are recognised mainly in southern Africa, where a number of countries have been able to control FMD by separating infected buffalo from livestock and by limited use of vaccination (Brückner et al., 2002; Thomson et al., 2003). Lack of movement control within countries and across international borders for both wildlife and domestic animals aggravates the problem, and gives credence to the fact that FMD will remain a problem on the sub-continent for the foreseeable future. With the increase in international travel, the threat from illegally smuggled bushmeat and other livestock products cannot be ignored, and it is imperative to understand the current epidemiology of FMD to predict what strains are currently most likely to pose a threat to disease-free regions. Six of the seven serotypes of FMD virus occur on the African continent (Vosloo et al., 2002), with the exception of Asia-1, which complicates control of the disease by vaccination. In sub-Saharan Africa, two cycles of FMD occur, one where virus circulates between wildlife hosts and domestic animals and the other where the virus spreads among domestic animals, without the involvement of wildlife (Vosloo and Thomson, 2004). In southern Africa and to a large extent, eastern Africa, the cycle between wildlife and domestic animals occurs, while in West Africa, due to the low numbers of wildlife, the disease is maintained predominately in domestic animals. However, once disease crosses from wildlife into domestic animals, a domestic cycle could be maintained without the involvement of wildlife. As it is costly to sample wildlife, very little is known about the FMD virus populations circulating in these animals and most information outside southern Africa is based on isolates obtained from domestic animals. Molecular epidemiological studies have contributed in planning control strategies by elucidating historical and current disease transmission patterns within and between countries. Furthermore, it is 149
