Immunogenetic influences on tick resistance in African cattle with particular reference to trypanotolerant N'Dama (Bos taurs) and trypanosusceptible Gobra zebu (Bos indicus) cattle

In sub-Saharan Africa, tick infestation and tick-borne infections together with tsetse-transmitted trypanosomosis arguably constitute the main parasitological disease complex constraining livestock production. Resistance to tick attack and tick-borne micro-organisms (TBMs) varies among different breeds of cattle. The magnitude of losses due to these parasites is related to an extent to the degree of breed resistance. Generally, zebu (Bos indicus) cattle possess a higher resistance to ticks and TBMs than European (Bos taurus) cattle. The host's immune system would appear to be the single most important factor that regulates this resistance. This paper reports on the main effector immune mechanisms governing resistance against ticks and TBMs. The cellular immune response appears more effective and stable than humoral immunity in modulating resistance to ticks and TBMs. Similarities between the immune mechanisms employed by trypanotolerant N'Dama (B. taurus) cattle, when infected with trypanosomes, and those elicited by tick bites and TBMs seem to exist, particularly at the skin level in the early phases of parasitic invasion. Moreover, there is evidence that in the N'Dama breed, resistance against ticks per se also has a genetic basis. Therefore, the N'Dama appears to be a unique breed in that it exhibits resistance to several parasitic diseases and/or infections, including helminths, when compared to other cattle breeds in West Africa. It is concluded that the multi-parasite resistant traits of the N'Dama breed should be exploited in those areas where trypanosomosis, ticks and tick-borne diseases constrain animal production. This should be of benefit for low-input farming systems where the use of chemicals for prophylaxis and therapy is limited by their relatively high cost. Additionally, the potential contribution of multiple disease resistant N'Dama cattle should be considered in crossbreeding programmes with exotic dairy breeds for increasing milk production in West Africa. (C) 2000 Elsevier Science B.V.