Infestation with the filarial worm, Onchocerca volvulus, found in many parts of tropical Africa, in Central and South America, and in the Yemen and Saudi Arabia. After a period of 9–18 months, the young worms, injected into the body by the bite of an infected gnat, mature, mate and start producing young microfilariae. These produce the characteristic features of the disease: an itching rash and nodules in different parts of the body. It may invade the optic nerve of the EYE and cause blindness; hence the name of African river-blindness. Treatment is with diethylcarbamazine and suramin. An international campaign is underway in an attempt to destroy the VECTOR in affected zones (see also FILARIASIS).