Spillover Infection in African Wildlife Species
Transmission of BTB to spillover hosts is a “downstream” event in the epidemic curve of the disease in maintenance host(s), and its occurrence is dependent on a high prevalence of the disease in these hosts.
In instances where an infected buffalo population has decreased markedly in size due to events such as drought or poaching, the prevalence of BTB in them, at best, was only slightly reduced or remained unchanged (de Vos et al. 2001; Kalema-Zikusoka et al. 2005), and they sustain the infection irrespective of the decrease in the number of animals.Only a small number of the wildlife species diagnosed with BTB appears to play a role in the dissemination and maintenance of the disease. It is also difficult to predict whether infected spillover species may be responsible for transmission of the infection at the wildlife/livestock interface, but there is always a risk that they may transmit the disease to other species in one way or another.
To date, 26 spillover species have been reported (Table 5.1). It is likely that the disease may not have been reported in a number of species, while there may be those in which the disease has not been diagnosed. One can therefore expect that the number of African wildlife species infected with M. bovis will increase as time goes on.
Unless the conservation status of the infected spillover species is threatened or endangered, BTB is not likely to have a negative effect on their populations. Individual infected animals, however, will suffer the consequences of the infection.
5.5