The disease is characterized by nodular tumors on the head. [male] and [female] Onchocerca caecutiens are found in the tumors. Three species of Eusimulium, probably E. avidum, E. ochraceum, and E. mooseri, transmit the disease. All stages of the parasite have been found in the flies. Mosquitoes pierce deeper than the flies in biting and thus may be mechanically incapable of transmitting the disease. The saliva of mosquitoes may be detrimental to the parasites. Disturbances of vision and microfilariae in the iris and conjunctiva were noted. The tumors can be removed to alleviate the condition. Plasmoquin and quinine both kill the microfilariae in vitro.