Situation and trends
Onchocerciasis is caused by infection with a filarial nematode (Onchocerca volvulus) transmitted by infected blackflies (Simulium spp.) that breed in fast-flowing rivers and streams. The adult worms produce embryonic larvae (microfilariae) that migrate to the skin, eyes and other organs. Although most onchocerciasis occurs in sub-Saharan Africa, the infection also occurs in Yemen and two out of six original endemic countries in Latin America (the Bolivarian Republic of Venezuela and Brazil).
In the Africa Region, the Onchocerciasis Control Programme in West Africa (OCP) operated from 1974 to 2002. This was followed by the African Programme for Onchocerciasis Control (APOC) which operated from 1995 to 2015. It targeted endemic countries that were not covered by the OCP. In 2016 the Expanded Special Project for the Elimination of Neglected Tropical Diseases in Africa (ESPEN) was launched. It will continue to assist onchocerciasis elimination programmes in addition to assisting programs for other preventative chemotherapy neglected tropical diseases. In 2015, more than 112 million people were treated with ivermectin in Africa, using the community-directed treatment with ivermectin strategy developed by APOC.
In the Region of the Americas, the Onchocerciasis Elimination Program of the Americas (OEPA) was launched in 1992 under the Pan American Health Organization (PAHO) Directing Council resolutions CD48.R12 and CD49.R19 with the goal of interrupting onchocerciasis transmission in six endemic countries in Latin America by 2015. By 2016, four countries had been verified by WHO as having interrupted the transmission of onchocerciasis: Mexico (2013), Ecuador (2014), Mexico (2015) and Guatemala (2016). In 2015, Brazil and the Bolivarian Republic of Venezuela treated about 20 thousand people with ivermectin.
In the Eastern Mediterranean Region, Yemen mapped known areas of transmission using the Ov-16 serologic test. It launched its first mass drug administration with ivermectin in 2016 with the goal of eliminating the disease.