HOST-RANGE AND THE MAINTENANCE OF HAEMONCHUS SPP. IN AN ADVERSE ARID CLIMATE

Three Haemonchus species (Haemonchus contortus, Haemonchus placei and Haemonchus longistipes) live in sympatry in Sahelian areas such as Mau ritania (West Africa). Four host species (dromedary, zebu cattle, shee p and goats) share the same pastures for several months per year. Expe rimental infection by H. contortus or H. placei was achieved only poor ly in dromedaries, and H. contortus or H. longistipes infection failed to establish in zebu cattle. Conversely, H. placei and H. longistipes successfully infected sheep and goats. Under field conditions, mixed congeneric infections were very rare in dromedaries but frequent in ze bu cattle (H. contortus represented 16% of Haemonchus spp. burden), in sheep (H. placei: 15%) and in goats (H. placei: 9% and H. longistipes : 6% of worms). The importance of the different host species was evalu ated for Haemonchus spp.: small ruminants are the main hosts of H. con tortus, dromedaries harboured the large majority of H. longistipes wor ms but 5% of them were found in goats which seemed to be additional ho sts. The most striking finding was the role played by the small rumina nts in the survival strategy of H. placei in Sahelian regions: 56% of the total of H. placei worms were found in sheep, 34% in goats and onl y 10% in zebu cattle. These results are consistent with the hypothesis that the extension of host range plays an important role in the survi val strategy of H. placei, whereas H. longistipes or H. contortus migh t well survive utilising their usual hosts. (C) 1998 Australian Societ y for Parasitology. Published by Elsevier Science Ltd.