Loa loa parasites are found in West and Central Africa. The east-west geographical distribution of the disease extends from southeastern Benin to southern Sudan and Uganda. The north-south geographical distribution extends from about 10°N to Angola. It is estimated that between 3 and 13 million people in West and Central Africa are infected.

The people most at risk for loiasis are those who live in the high-canopied rain forests of West and Central Africa. The deerflies that transmit the parasite typically 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 create a favorable environment for the deerflies, as the trees form a dense canopy. The flies do not typically enter homes, but might be attracted to homes that are well lit.

Travelers to at-risk areas who stay for long periods of time are more likely to become infected than short-term travelers, though a few cases have been documented in persons who were in at-risk areas for less than one month. A traveler's risk for infection likely will depend on the number of bites received and the number of infected deerflies in the area visited.