Onchoceriasis or river blindness

Map showing where riverblindness is endemic

Onchoceriasis or river blindness is the world's second leading infectious cause of blindness. It is caused by Onchocerca volvulus, a parasitic worm, that breeds in water and that can live for up to fourteen years in the human body.
Controlling insect breeding sites in rivers is one of the pillars of prevention. The disease is transmitted from one person to another through the bite of a black fly (Simulium).

Symptoms of the disease in a person usually begin to show 1-3 years after infection. Each adult female worm, which can be more than half a meter in length, produces millions of microscopic young worms (microfilaria). The microfilaria 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.
 

Onchoceriasis is found in 36 countries in Africa as well as in Guatemala, southern Mexico, some areas of Venezuela, small areas in Brazil, Colombia and Ecuador, and in the Arabian peninsula. A total of 18 million people are affected worldwide.

Click here to learn for more information about waterborne diseases, dimension of the problem, transmission, prevention.

Sources:
http://www.who.int/water_sanitation_health/diseases/oncho/en/
http://en.wikipedia.org/wiki/Onchocerciasis
  Picture:
http://images.google.com/images?hl=en&rls=GGLD,GGLD:2005-12,GGLD:en&q=onchocerciasis&spell=1