<unk>  is a filarial (arthropod-borne) nematode (roundworm) that causes<unk> asis (river blindness), and is the second-leading cause of blindness due to infection worldwide after trachoma. It is one of the 20 neglected tropical diseases listed by the World Health Organization, with elimination from certain countries expected by 2020. John O’Neill, an Irish surgeon, first described<unk>  in 1874, when he found it to be the causative agent of ‘craw-craw’, a skin disease found in West Africa. A Guatemalan doctor, Rodolfo Robles, first linked it to visual impairment in 1917. O.<unk>  is primarily found in sub-Saharan Africa, and humans are the only known definitive host. It is spread from person to person via female biting blackflies of the genus Simulium.
Onchocerca volvulus
Trichuris trichiura
Schistosoma intercalatum
Hymenolepis diminuta
Trichinella britovi
Schistosoma haematobium
Echinostoma
Taenia saginata