Epidemiology & Risk Factors

Loa loa parasites are found in West and Central Africa. Ten countries have areas where there are high rates of infection (i.e., where more than 40% of the people who live in that area report that they have had eye worm in the past). An estimated 14.4 million people live in these areas of high rates of infection. Another 15.2 live in areas where 20–40% of people report that they have had eye worm in the past.

More on: WHO-ESPEN: Loa Loa Data and Distribution Maps Provided by Health Ministriesexternal icon

The people most at risk for loiasis are those who live in the certain rain forests in West and Central Africa. The deerflies that pass the parasite to humans usually bite during the day and are more common during the rainy season. They are attracted by the movement of people and by smoke from wood fires. Rubber plantations are areas where more deerflies may be found. The flies do not typically enter homes, but they might be attracted to homes that are well lit.

Travelers are more likely to become infected if they are in areas where they are bitten by deerflies for many months, though occasionally they get infected even if they are in an affected area for less than 30 days.

Your risk of infection depends on the number of bites received, the number of infected deerflies in the area you visit, and the length of your stay in the area.

Page last reviewed: September 22, 2021