Tuberculosis in wild and domestic animals in South Africa

Abstract

Bovine tuberculosis is an endemic disease with a low prevalence in South African cattle. This is mostly the result of a national bovine tuberculosis control scheme which has been in place for nearly 40 years and has prevented outbreaks from spreading and causing large-scale losses, thereby also minimising the risk in view of human health. However, with the establishment of African buffalo as a successful wildlife maintenance host a new, yet undetermined risk factor has been introduced. It poses an entirely new challenge on national and provincial authorities to meet the 'fit for purpose' principle in terms of reducing economic losses but also the potentially negative impact on conservation efforts and, most of all, to protect human health and livelihoods.

There is a need to shift the focus of bovine tuberculosis control from an exclusively cattle based to an integrated strategy, which takes into consideration the wildlife reservoir and the added risk of Mycobacterium bovis transmission between cattle and buffalo populations. In order to justify such a change in strategy, data regarding the epidemiology of bovine tuberculosis in wildlife reservoirs need to be available to underpin the interdependence of bovine tuberculosis in livestock and wildlife. This thesis describes the establishment of a set of molecular tools for researching the epidemiology of bovine tuberculosis in both livestock and wildlife and their crucial contribution to insight in the genetic diversity of M. bovis in South Africa. Furthermore it was demonstrated beyond doubt that spillover of M. bovis from cattle to wildlife has occurred and revealed important clues on the course of the epidemic within the Kruger National Park by intra- and interspecies spread of one dominant M. bovis strain.

Evaluation of new and improved diagnostic methods based on both the cellular immunity and humoral immune response were undertaken and showed that especially the gamma interferon assay holds a high potential for more practical and reliable testing of buffalo and cattle for bovine tuberculosis than conventional approaches. In the long-term, all diagnostic assays applied and evaluated will play a crucial role in the implementation and monitoring of a suitable control strategy in wildlife as well as cattle. The principal aim for controlling bovine tuberculosis is to eliminate the risk of infecting humans, but also to protect biodiversity in indigenous wildlife. Ultimately vaccination will be the most feasible, economical and ethically acceptable control option in South Africa and work presented in this thesis has resulted in both an experimental intratonsilar infection model in buffalo and provided the first insight into the immune responsiveness of buffalo to vaccination with BCG Pasteur vaccine. Both developments present crucial milestones in gaining a better understanding of the factors influencing the efficacy of vaccination regimens in this wildlife reservoir.