River blindness. Caused by the parasitic worm onchocerca. Infection is as a result of being bitten by the buffalo gnat which is found in some fast flowing rivers in Africa and Central America.
Adult worms can live up to 15 years beneath the skin of its victim and produce millions of embryos which spread through the body including the eye. Worldwide there are approximately 20 million people infected. Even dead embryos can cause severe itching and blindness. To date no drug has been found to kill the adult worm however, blindness can be prevented.