Onchocerciasis

**Definition:** Any condition caused by an infection with the parasitic worm Onchocerca volvulus. These conditions are characterised by the presence of firm subcutaneous nodules filled with adult worms, pruritus, long-term corneal inflammation (keratitis), or thickening of the corneal stroma. If untreated, these infections will lead to blindness. Transmission is through the bite of an infected Simulium fly.

**Long definition:** Disease transmitted through the bites of infected blackflies of Simulium species, which carry immature larvae of the filarial worm Onchocerca volvulus. The larvae form nodules in host subcutaneous tissue, where they mature to adult worms. After mating, the female adult worm can release up to 1000 microfilariae a day, which cause a variety of conditions, including blindness, skin rashes, lesions, intense itching and skin depigmentation.