Onchocerciasis is the result of infection by the filarial Onchocerca volvulus. The infection is conveyed by flies of the genus Simulium, which breed in rapidly flowing, well-aerated water. Adult flies inflict painful bites during the day, both inside and outside houses. While feeding, they pick up the microfilariae, which mature into the infective larva and are transmitted to a new host in subsequent bites. Humans are the only known hosts.
Onchocerciasis is endemic in sub-Saharan Africa, Yemen and a few foci in Central and South America. Itis estimated that 17.7 million people are infected, of whom 500 000 are visually impaired and 270 000 blind.
Due to onchocerciasis, huge tracts of fertile land lie virtually untilled, and individuals and communities are impoverished.
After inoculation of larvae by a bite from an infected fly, the worms mature in 2–4 months and live for up to 17 years in subcutaneous and connective tissues. At sites of trauma, over bony prominences and around joints, fibrosis may form nodules around adult worms, which otherwise cause no direct damage. Innumerable microfilariae, discharged by the female O. volvulus, move actively in these nodules and in the adjacent tissues, are widely distributed in the skin, and may invade the eye.
Live microfilariae elicit little tissue reaction, but dead ones may cause severe allergic inflammation, leading to hyaline necrosis and loss of collagen and elastin. Death of microfilariae in the eye causes inflammation and may lead to blindness.
The medicines that can be thought of use are:-