Loiasis is endemic in West and Central Africa, and is found particularly in the "rain forest areas of the Sudan, the basin of the Congo, and [throughout] West Africa to include Cameroon and Nigeria (Markell, et al., pg 321). The map on the left illustrates the distribution of the disease (courtesy of
http://www.biosci.ohio-state.edu/~parasite/loa.html). This distribution has much to do with the habitat of the vector, three species of Chyrsops flies, although recent evidence has shown that an American deerfly, Chrysops atlanticus, can host Loa loa.
To the left is another map from the aforementioned website of the Foci of Loiasis infection. An estimated 9 to 70% of adults in hyperendemic areas are infected, and the total infected is estimated 13 million people. Almost all infected persons live in the rainforests of central Africa.
Please see the Public Health and Prevention page for more information regarding this topic.