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

In sub-Saharan Africa, tick infestation and tick-borne infections together with tsetse-transmitted trypanosomosis arguably constitute the main parasit ological disease complex constraining livestock production. Resistance to t ick attack and tick-borne micro-organisms (TBMs) varies among different bre eds 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 ta urus) cattle. The host's immune system would appear to be the single most i mportant factor that regulates this resistance. This paper reports on the m ain effector immune mechanisms governing resistance against ticks and TBMs. The cellular immune response appears mote effective and stable than humora l immunity in modulating resistance to ticks and TBMs. Similarities between the immune mechanisms employed by trypanotolerant N'Dama (B, taurus) cattl e, when infected with trypanosomes, and those elicited by tick bites and TB Ms seem to exist, particularly at the skin level in the early phases of par asitic invasion. Moreover, then is evidence that in the N'Dama breed, resis tance 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 para sitic diseases and/or infections, including helminths, when compared to oth er cattle breeds in West Africa. It is concluded that the multi-parasite re sistant 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 c hemicals for prophylaxis and therapy is limited by their relatively high co st. 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 Elsevi er Science B.V. All rights reserved.