Epidemiology & Risk Factors

Onchocerca infections are found in tropical climates. The main burden is in 31 countries in sub-Saharan Africa. The list of 31 African countries can be found on the World Health Organization (WHO) Onchocerciasis Fact Sheetexternal icon website. The parasite is also found in limited areas in South America and in Yemen in the Middle East. In the Americas, four countries have been verified by the World Health Organization (WHO) as free from onchocerciasis: Colombia, Ecuador, Mexico, and Guatemala.   Only a single small transmission zone remains in South America, crossing the border between the Bolivarian Republic of Venezuela and Brazil.. The Global Burden of Disease Study estimated that in 2017 there were at least 20.9 million people are infected worldwide, of which 14.6 million had skin disease and 1.15 million had vision loss.

The people most at risk for acquiring onchocerciasis are those who live or work 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 in the countries mentioned previously. Usually, many bites are needed before becoming infected. Therefore, those travelers to at-risk areas most likely to become infected are long-term missionaries, Peace Corps volunteers, field researchers, and other long-term travelers.