Onchocerciasis, or river blindness , is caused by a certain type of filarial worm. It is transmitted from human to human through the bites of infected blackflies. The larvae form nodules under the skin, where they mature to adult worms. After mating, each female adult worm can release up to 1,000 offspring per day. These move through the body, and when they die they cause a variety of conditions, including blindness, lesions, and intense itching.