Epidemiology & Risk Factors
Onchocercal infections are found in tropical climates. The main burden is in sub-Saharan Africa, though the parasite is found in limited areas in the Americas and in Yemen in the Middle East. The World Health Organization (WHO) estimates that 37 million people are infected with O. volvulus worldwide; of these people 270,000 are blind and 500,000 have some sort of visual impairment. Some 90 million people are at risk for becoming infected with the parasite.
The people most at risk for acquiring onchocerciasis are those who live near streams or rivers where there are Simulium blackflies. Most of the areas where the blackflies are found are rural agricultural areas in sub-Saharan Africa. Usually, many bites are needed before being infected, so people who travel for short periods of time (generally less than 3 months) to areas where the parasite is found have a low chance of becoming infected with O. volvulus. Those travelers to at-risk areas most likely to become infected are long-term missionaries, Peace Corps and other long-term volunteers, and field researchers.