Onchocerciasis (or river blindness) affects up to 37 million people worldwide and is most abundant in Africa. It is responsible for skin disease and blindness. It is caused by a large worm (known as Onchocerca volvulus) which is transmitted to humans via black flies which breed in rivers and streams – hence the name river blindness.

Life Cycle

Onchocerciasis is transmitted by black flies which live and breed in rivers. When an infected black fly bites, infective larvae crawl into the bite wound. These migrate through the skin tissue and mature into adult worms located under the skin in self-contained nodules (onchocercomas). New worms can form new nodules or will cluster together in existing nodules. If the site of the worm nest is over bone – such as the skull, hips or knee – then a prominent nodule can appear. The smaller male worm (about 4cm long) may migrate between nodules when mating with the larger females (about 40 cm long). A female worm is capable of producing up to 1,000 larvae per day. These are able migrate through skin tissues all around the body.


Symptoms occurs when worms die within the skin which results in inflammation of the skin. This can cause intense itching, dermatitis and depigmentation; this create conditions like lizard skin and leopard skin. If the larvae migrate to the eye their death results in inflammation leading ultimately to blindness.