Onchocerciasis or river blindness is a parasitic disease with an insect vector that breeds in water. It is the world's second leading infectious cause of blindness. Controlling insect breeding sites in rivers is one of the pillars of prevention.

Onchocerciasis or river blindness is a parasitic disease caused by Onchocerca volvulus, a thin parasitic worm that can live for up to 14 years in the human body. The disease is transmitted from one person to another through the bite of a blackfly (Simulium)

Each adult female worm (macrofilaria), which can be more than ½ metre in length, produces millions of microscopic young worms (microfilariae). The microfilariae migrate through the skin and, upon death, cause intense itching and depigmentation of the skin (“leopard skin”), lymphadenitis resulting in hanging groins and elephantiasis of the genitals, serious visual impairment, and blindness when they reach the eye.

The blackfly lays its eggs in the water of fast-flowing rivers, which mature into adult blackflies in 8 to 12 days. The female blackfly typically seeks a bloodmeal after mating and, upon biting a person who is infected with onchocerciasis, may ingest worm larvae, which can then be passed on to the next person bitten by the blackfly. Eventually, the transmitted worm larvae develop into adult worms and settle into fibrous nodules in the human body close to the surface of the skin or near the jointst.

There are two main actions undertaken against onchocerciasis control: spraying of breeding sites in water of the blackflies with larvicides, and the treatment of patients with a drug (ivermectin) that kills the young worms.

Source: WHO