Review/Oorsig Volume 23, Issue 02 - Page 9

Volume 23 • Issue 02 • 2019 Moreover, international perceptions concerning FMD, not to mention control strategies/norms and trade standards, are almost exclusively based on Eurasian type FMD. That situation makes life difficult for countries like Botswana, Namibia and South Africa. The extent of the differences between the SAT and Eurasian lineages, my colleagues and I have shown, renders the eradication of SAT viruses in Southern Africa technically difficult, if not impossible, using currently available technology, i.e. unlike the situation with the Eurasian types. The implication is that in the long term FMD will be eradicated from most parts of the world but not Southern Africa. Differences between SAT and Eurasian FMD The ability to manage effectively and/or eradicate transboundary animal diseases, of which FMD is a prime example, is dependent primarily on three factors: (1) the epidemiology of the disease, (2) the ability to identify accurately the presence of the infection and (3) the availability of effective control measures. In all three respects the SAT and Eurasian lineages of FMD viruses differ significantly. Differences between the two FMD virus lineages were first remarked upon in 1932 by Prof P.J. du Toit, former Director of Onderstepoort Veterinary Research and Dean of the Faculty of Veterinary Science, University of Pretoria. Prof du Toit was asked by the British Government to investigate the first outbreak of FMD in what is now south-eastern Zimbabwe following the Great Rinderpest Pandemic of 1896-1904. That pandemic decimated both cattle and buffalo populations of the subcontinent. Although at that time the role of buffalo, or the existence of different FMD virus types was unknown, Prof du Toit concluded that the FMD he investigated in Zimbabwe was ‘different’ from the FMD that was then widespread in Europe. This difference related mainly to the slow and inefficient spread of the disease between infected and susceptible cattle herds in close contact with each other on Nuanetsi Ranch, i.e. in contrast to the rapidly spreading nature of the disease in Europe. Apart from the unique association between SAT viruses and African buffalo and the inefficient transmission of these viruses between infected and susceptible cattle, there are other important differences between the two viral lineages. These include (1) the tendency for SAT outbreaks in cattle to cause mild or unapparent disease in only a small proportion of the exposed population; often below 1% and (2) the differing importance of carrier animals of various species in maintaining the infection (where current indications are that although carrier buffalo are important in maintaining SAT viruses within breeding herds of buffalo, cattle are not involved in carrier transmission). However, the ‘carrier’ status of different ruminant species is a contentious issue, unresolved by over 100 years of investigation. (3) The third difference relates to the wider range of virus variants and lack of identified subtypes within SAT viruses that, in contrast to the Eurasia types, makes the manufacture of vaccines that ‘match’ the wide variety of viruses present in the field difficult. Relationship between FMD viruses and wildlife Figure 2 summarises what could be referred to as the ‘Southern African FMD triangle’ involving SAT viruses maintained primarily by African buffalo but also transmissible to other cloven-hoofed wildlife species and domestic livestock. Fig 2. Spread of FMD between African wildlife and livestock in Southern Africa 9