Geographical distribution of O.<unk>  as of March 2017: Endemic countries are shown in red, previous endemic countries in blue, and countries with no local cases in orange. An estimated 187 million people are at risk of O.<unk>  infection, with 17–25 million people infected and 0.8 million showing some impairment of vision. O.<unk>  has not directly caused a single death, but has cost 1.1 million disability adjusted life years, which measure the number of years of healthy life lost due to a specific disease and show the burden of a disease. Simulium blackfly adults require moving water to breed and eggs remain in water until they exit from the pupa and enter the adult stage of their lifecycle. Due to this restriction, O.<unk>  is only found around streams or rivers. Artificial water systems, such as hydroelectric power plants, built in Africa, provide ideal conditions all year for blackfly development and make controlling its spread difficult. About 99% of cases of<unk> asis are found in 31 countries in sub-Saharan Africa, although areas of limited transmission occur in Brazil, Venezuela, and Yemen. The disease is thought to have been imported into Latin America through the slave trade.<unk> asis was eliminated from Colombia in 2013, Ecuador in 2014, Mexico in 2015, and Guatemala in 2016 due to control programs that used mass drug administration with ivermectin.
Onchocerca volvulus
Trichuris trichiura
Schistosoma intercalatum
Hymenolepis diminuta
Trichinella britovi
Schistosoma haematobium
Echinostoma
Taenia saginata