Onchocerciasis in the Blue Nile Valley of western Ethiopia.

In a survey among 477 inhabitants of the Blue Nile Valley of western Ethiopia 182 (38%) were positive by skin snip investigation for microfilariae of Onchocerca volvulus. Of these only 23% had typical clinical signs and symptoms of onchocerciasis. The highest prevalence rate of microfilariae (84%) was found among Nilotics in the lowlands, where 50% of the children above 10 years, and 90% of adults above 30 years of age, were infected. The mean microfilarial density per skin snip was significantly higher in the high prevalence areas (14) than in the low prevalence areas (3). Positive skin snips from both hip and shoulder were found in 24% of the population, whereas 3% had microfilariae only in the shoulder and 11% only in the hip region. The mean microfilarial density in the hips (16) was double that in the shoulders (8). Ophthalmological evaluation, including slit lamp examination, was possible in 77 of the 182 cases with positive skin snips. Severe eye damage due to onchocerciasis was not observed. However, one 35 year old female had live microfilariae in the anterior chambers of both eyes.