Distribution of microfilariae in Guatemalans with onchocerciasis.

Ten Simulium ochraceum were allowed to feed at 10 different sites on 12 Guatemalans with onchocerciasis, and skin snips were taken from six of these sites. Numbers of microfilariae (mff) ingested by the flies and mff emerging from skin snips were highly correlated and showed that concentrations were greatest on the torso and decreased peripherally. S. ochraceum ingested the number of mff present in 1.0 mg or under 1.5 mm2 of skin. Numbers of mff in skin snips from the head, shoulder and upper arm correlated with over-all levels of infection but were frequently negative in subjects with light infections. Two or more skin snips were best able to detect and quantify infections.