Onchocerciasis infects approximately 13 to 20 million persons, rendering 1 to 5% of them blind. The vast majority of the afflicted live in tropical Africa, over half of these in Nigeria and Congo. Foci of infection are also found in Yemen, Saudi Arabia, and Latin America from southern Mexico through the northern half of South America. It has beensuggested that the disease was introduced into South America by West Africans enslaved and transported to the New World for the purpose of mining gold in the mountain streams of Venezuela and Colombia. The Central American foci date from Napoleon III’s use of Sudanese troops to support his invasion of Mexico in 1862. The disease still persists on the high slopes of the Sierra, where coffee plantations lie along the rapidly flowing streams that serve as breeding places for Simulium species.