Onchocerciasis Background
Onchocerciasis is an infection caused
by the nematode Onchocerca volvulus. Humans acquire onchocerciasis
through the bite of Simulium blackflies. Because the fly develops and
breeds in flowing water, onchocerciasis is commonly found along rivers
and is sometimes referred to as river blindness.
Onchocerciasis is not acquired in the
United States. Occasional cases are found in immigrants or travelers
from endemic areas. However, symptomatic onchocerciasis usually requires
heavy infestations and repeated exposure to the vector fly. Short-term
travelers are at little or no risk of the disease. Pruritus, dermatitis,
and eosinophilia may occur in travelers who stay longer than 3 months in
endemic areas of Africa. Symptoms may occur months to years after
leaving the endemic area.
Currently, onchocerciasis is endemic
to 30 African countries, Yemen, and in localized foci of 6 Central and
South America countries. Globally, approximately 18-36 million
individuals have onchocerciasis, 99% of whom reside in Africa. The World
Health Organization (WHO) estimates that 750,000 people are blind or
have reduced vision as a result of the disease.