Trypanotolerance in cattle and prospects for the control of trypanosomiasis by selective breeding.

Tsetse-transmitted trypanosomiasis is one of the major constraints on the expansion of the livestock and agricultural industries in Africa. The disease affects animals and man, with direct and indirect losses estimated in billions of dollars annually. Because of the phenomenon of antigenic variation, no vaccine is available. Current prophylactic efforts must rely on tsetse control by the use of insecticides and on trypanocidal drugs. However, recent advances in our knowledge of tsetse and trypanosome biology are offering hope for alternative methods of trapping tsetse, new drugs and even vaccination. Possibly of even greater significance is the increasing sense that Africa herself might be able to contribute to the resolution of this problem. Over a period of several thousand years, she has generated cattle, such as the taurine N'Dama and West African Shorthorn breeds of West and Central Africa, that are now known to possess a significant degree of innate resistance to trypanosomiasis and several other important infectious diseases. These cattle are extremely well adapted to the environment and are now recognised as having considerable production potential. The ability to resist the development of anaemia in the face of infection, as assessed by packed red cell volume percent (PCV), has been shown to be correlated with the capacity to be productive, thereby identifying regulation of PCV as a key trait of trypanotolerance. Thus, an estimate of the ability of an infected animal to maintain PCV, following either experimental or field infection, could be used as a method for identifying trypanotolerant individuals. This could provide a means of estimating trypanotolerance heritability, thereby permitting rational breeding programmes to be instituted. Africa may thus provide the answer.