"Tuberculosis – What Makes it an Ideal Disease for the Interface?"

Anita Michel

In recent years it has become evident that the role of wildlife in the epidemiology of bovine tuberculosis (BTB) has been greatly underestimated, both in developing countries as well as in the developed world. With the breakdown of traditional control programmes and a lack of an effective vaccine, it is almost impossible for affected countries to eradicate or even prevent the further spread of this chronic disease.

Compared to developed countries, where economic losses in the livestock production sector represent the most serious effect of M. bovis infection at the wildlife-livestock interface, the range of implications can be much broader in developing countries.

In South Africa, the two largest game reserves, the Kruger National Park (KNP) and the Hluhluwe-Umfolozi Park (HUP), have become endemically infected with bovine tuberculosis after the disease has spilled over from domestic cattle during the second half of the 20th century. Although African buffalo (Syncerus caffer) are the main reservoir in both cases, other species have recently shown potential to serve as maintenance hosts. Apart from the impact of this disease on the conservation of endangered species, on the genetic diversity within infected species, and on the economic impact with regards to international trade, tuberculosis caused by M. bovis poses a direct health threat to communities living along the border of infected ecosystems. The prevalence of bovine tuberculosis in communal cattle is currently unknown for most of the areas, but the risk of M. bovis transmission from wildlife is rapidly increasing as exceedingly high herd prevalences are reached in buffalo and as the spectrum of affected wild animal species becomes broader. Against the generally proclaimed reduced susceptibility of humans to M. bovis, the human-livestock interface in this particular case should be considered a favourable environment for zoonotic tuberculosis because immuno-suppression due to infection with HIV/AIDS can pave the way for infectious agents otherwise unable to cause disease on their own.

Along the borders of KNP and HUP, an estimated 165,000 people are living in close contact with and consume products from cattle with an unknown BTB status, but which form part of the wildlife-livestock-human triangle.