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Genetic resistance to African trypanosomiasis occurs in certain breeds of livestock, many species of wildlife, some strains of mice, and possibly humans. The term trypanotolerance is used to describe this trait, which in domestic livestock is best exhibited by the indigenous West African taurine breeds of cattle, N'Dama and West African Shorthorn, that have been in Africa for 5,000 to 7,000 years. Confirmation not only that these breeds are genetically resistant to trypanosomiasis but also that they are at least as productive as other indigenous breeds is currently leading to their increased use in livestock-development projects in tsetse-infested areas. Trypanotolerance appears to be related to the control of parasitemia, a capacity associated with an event that regulates parasite growth and determines how rapidly the immune response is triggered. Identification of the factors that regulate this event and definition of their genetic basis may have important implications for the development of novel strategies for control of African trypanosomiasis.

Studies have been made in two main areas of genetic research on African trypanotolerant (N'Dama) cattle. The first is of the significance for performance and the heritability of trypanotolerance traits and the second is the search for markers of the breed type and the traits of interest. Results demonstrate significant effects of the ability of an animal to control parasitaemia and anaemia on its performance. Initial estimates suggested that parasitaemia measures had a very low heritability, but ability to maintain packed cell volume levels when detected as parasitaemic and to generate an immune response could form the basis of a practical selection approach. The search for markers has so far concentrated on the major histocompatibility complex and on a polymorphic system of common leukocyte antigens. Phenotypes that appeared more characteristic of the N'Dama in comparison with those of East African zebu cattle were examined for associations with trypanotolerance traits. One major histocompatibility complex encoded phenotype and two common leukocyte antigens gave indications of important associations. Planned research will further characterise the breed and define traits of importance to assist in increasing its productivity in Africa and thus in its conservation. The addition of a molecular genetics component to an integrated genetics research programme, principally through involvement in development of a linkage map of the bovine genome, will strengthen these efforts and make it possible to conserve specific N'Dama genes related to productivity.