Bovine onchocercosis in north Cameroon.

Ventral skin biopsies from 204 Gudali cattle of the Vina division in the Adamawa highlands revealed microfilariae of Onchocerca gutturosa, O. ochengi and O. dukei in 85%, 51% and 8% of the animals, respectively. In 60 Fulani cattle from the Tcholliré division in the Sudan savanna, the same microfilaria species were detected in 92%, 83% and 47% of the animals. Onchocerca armillata adult worms were found in 67% of the Gudalis and in 100% of the Fulanis. In areas of high transmission the prevalences declined in old animals, possibly indicating acquired resistance. For all species no significant difference in prevalence was found between male and female cattle. The microfilariae of O. ochengi and O. dukei were concentrated in the skin of the posterior and anterior belly, respectively. Onchocerca gutturosa microfilariae had highest densities on the hump and near the umbilicus, whereas those of O. armillata were distributed more evenly across the body surface. In infected hides the mean microfilarial densities of O. gutturosa, O. ochengi, O. dukei and O. armillata were respectively 3.1 microfilariae (mff) mg-1, 0.6 mff mg-1, 0.7 mff mg-1 and 0.092 mff mg-1 for the whole body surface and 9.3 mff mg-1, 3.8 mff mg-1 and 1.9 mff mg-1 for the sites of highest density (O. armillata had no predilection site). Ninety-five per cent of the microfilariae were located in the uppermost skin layer of 2 mm depth, 5% were in the corium and none were found in the subcutis. Two cattle had skin microfilariae of a hitherto unknown Onchocerca species.