African trypanosomiasis in cattle: working with nature's solution.

Both acquired and innate resistance to African trypanosomiasis can occur in cattle. The former raises the possibility of a vaccine against tsetsetransmitted metacyclic trypanosomes which have been shown to have a smaller repertoire of variable antigens than bloodstream parasites. The latter provides two further avenues of approach: firstly, trypanotolerant breeds are being increasingly exploited and improved by conventional management and breeding methods including embryo transfer; secondly, research is being carried out into the factors associated with their innate resistance, i.e., the control of trypanosome growth, the development of effective immune responses and resistance to anaemia. If the mechanisms underlying these factors are identified it might be possible by immunisation, by specific drug treatment or by transfection of appropriate genes to produce highly productive cattle resistant to trypanosomiasis.