Onchocerca volvulus

Onchocerca disease, also known as onchocerciasis or river blindness, occurs in Central Africa and Central and South America. The causative parasite is the nematode Onchocerca volvulus, transmitted to humans by bloodsucking blackflies which live by rivers. The adult female parasite, coiling in a lump formed under the human skin, produces larvae called microfilaria. When blackflies suck blood, the microfilariae move into the flies and grow to the stage infective to humans. When a blackfly sucks human blood again, microfilariae escape from the fly and invade the human through the wound of the bite. Microfilariae, moving around in the human body, cause severe itching, and a rash and spots on the skin. They sometimes invade the eye, and may cause blindness.