Infection with nematodes of the genus onchocerca. Characteristics include the presence of firm subcutaneous nodules filled with adult worms, pruritus, and ocular lesions. Onchocerciasis (ˈ|É’|Ĺ‹|k|ɵ|s|Éśr|ˈ|s|aÉŞ|.|É™|s|ɨ|s or Ë |É’|Ĺ‹|k|ɵ|s|Éśr|Ë |k|aÉŞ|.|É™|s|ɨ|s), also known as river blindness and Robles disease, is a parasitic disease caused by infection by Onchocerca volvulus, a nematode (roundworm). Onchocerciasis is second in the world only to trachoma as an infectious cause of blindness. The parasite is transmitted to humans through the bite of a black fly of the genus Simulium. The larval nematodes spread throughout the body. When the worms die, their Wolbachia symbionts are released, triggering a host immune system response that can cause severe itching, and can destroy optical tissue in the eye. Most infections occur in sub-Saharan Africa, although cases have also been reported in Yemen and isolated areas of Central and South America. As of 2001, an estimated 18 million people suffered from onchocerciasis, with approximately 270,000 cases of blindness related to the infection. Using case studies of coffee plantation workers in Guatemala, Robles hypothesized the vector of the disease is a day-biting insect, and more specifically, two anthropophilic species of Simulium flies found to be endemic to the areas. He published his findings on a “new disease” from Guatemala associated with subcutaneous nodules, anterior ocular (eye) lesions, dermatitis, and microfilariae in 1917. Treatment may involve the use of the drug ivermectin. For best effect, entire communities are treated at the same time. Since final hosts of O. volvulus are restricted to primates, it has no major animal reservoir. A single dose may kill first-stage larvae (microfilariae) in infected people, and it prevents transmission for many months in the remaining population. Other drugs are also available, including the tetracycline-class antibiotic doxycycline, which kills the Wolbachia and renders the female nematodes sterile. The removal of the palpable nodules is common in Guatemala, Ecuador, and Mexico. (An OSH glossary used in safety and health at work which is, adopted by ILO {102}.. The term definition has been obtained from the secondary source