Transmission patterns of onchocerciasis in southwest Ethiopia.

The three transmission patterns found till now in Ethiopia are described. The forest area contains ideal conditions for the breeding of Simulium, but the sparse human population makes the transmission rate low. Only a few people were found to be infected. The subsistence crop farming area is a less ideal habitat for the vector due to the scarcity of bush and shade. However the presence of a largest population can explain the slightly higher prevalence of the disease than in the forest. The coffee farming area is densely populated, rich in bush and shade, with heavy rainfall and numerous rivers. Here the number of Simulium and their chance to reach the infective stages, are considered to be high. A high prevalence of the disease was found in this zone.