Classification: ICD-9 125.3; ICD-B73

Syndromes and synonyms: River blindness, onchoder-matitis.

Agent: Onchocerca volvulus, a filarial nematode (roundworm). Adult female worm is approximately 50 cm long.

Reservoir: Humans are the only natural host. The parasite can be experimentally transferred to chimpanzees.

Vector: Female blackflies (Simulium). Transmission by S. damnosum complex in Africa is responsible for >95% onchocerciasis cases. S. neavei complex in East Africa and S. rasyani in Yemen. In Latin America: S. ochraceum (Mexico and Guatemala), S. exiguum (Colombia and Ecuador), S. metallicum (northern Venezuela), and S. guianeense (southern Venezuela and Brazil). Blackfly larvae develop in fast-flowing rivers and the adult fly’s flight range is up to 40 miles, explaining the patchy distribution of the disease. Aided by wind, blackflies can fly up to 500 km, explaining reinvasion of areas under control.

Transmission: By bite of the vector.

Cycle

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