Onchocerciasis in Plateau State; Nigeria: ecological background, local disease perception & treatment; and vector/parasite dynamics.

The physico-biological ecological complex in Plateau State has by definition increased the potential of most rivers to support the breeding and dispersal of vector species as well as human acquisition and dissemination of the disease for several months in a year. Though villagers in endemic areas are of the know of the nuisance of blackfly bites, but the majority of them lacked the aetiological knowledge of onchocercal lesion. Hence disease management is misdirected towards consulting the oracle and appeasing the gods. The vectors of onchocerciasis in Plateau State, S. damnosum, and S. sirbanum are wet season breeders with their peak biting density occurring at the height of rainy season. However, biting flies carry more infective parasites at the beginning and end of rain. These vectors exhibit bimodal biting activity: a small one in the morning hours and a pronounced evening peak. Biting activity is at least influenced by two major climatic factors; illumination and temperature. However, the fastest changing climatic factor relative to an increase in the biting activity of flies was illumination. Microfilarial load in the skin of patients does not significantly change throughout the year or when biopsies are taken under shade throughout the day. Extreme temperatures, however, have significant reducing effect on the skin microfilarial. The epidemiological relevance of these in the ongoing MECTIZAN delivery in the State are discussed.