Onchocerciacis, otherwise known as River Blindness, is caused by the intrusion of parasitic worms (Onchocera volvulus, for all you fans of latin genera) into the body. The worms are capable of surviving for fourteen years within a host, during which time they inject millions of microscopic larvae into the bloodstream.

It is the existence of the microscopic larvae that gives rise to the symptoms associated with River Blindness, and the subsequent transfer of the disease to others. Larvae migration relies upon the actions of the Blackfly--the flies (whose role here as a vector is reminiscent of the mosquito's Yellow Fever days) transfer the larvae by first ingesting them from the host during a bloodmeal and then transferring them to a different individual at a later feeding.

Typically, symptoms will manifest roughly three years after introduction of the worm. The most common include visual impairment (hence the name), depigmentation of the skin, and lymphadenitis (swelling of lymph nodes and vessels; also occurrs in elephantiasis).

River Blindness is most prevalent in Africa--nearly all people infected with the disease reside there (some 99 percent.) Many fertile river areas go abandoned for fear of infection by the high blackfly populations therein.

River blindness is a very nasty disease, indeed.

It's an eye and skin infection caused by the introduction of onchocerca volvulus worms into the bloodstream.

Worms in your blood.

Onchocerciasis

Onchoceriasis is known as 'river blindness' because its vectors — blackflies — breed in fast-moving rivers.

A blackfly becomes infected by biting a person with the worms. Over the next two weeks the worms develop inside the fly to a stage that is infectious to humans. When the fly bites again it injects onchocerca larvae which multiply in the bloodstream. That is river blindness.

Infected individuals may be without symptoms. Those who do exhibit symptoms experience itching, subcutaneous bumps, and eye lesions. Scar tissue from skin lesions coupled with furious scratching cause puckering and spotting of the skin. Worms that reach the end of their life cycle and die inside the eyes trigger an inflammatory response in the cornea, humors, and retina, eventually causing blindness. Diagnosis is made with a slit lamp, which reveals parasites swimming in the anterior chamber behind the lens.

Left untreated, the worms can live up to 15 years. Symptoms appear 9 to 24 months after infection. The World Health Organization says that 17 million worldwide are infected, nearly all of whom reside in Africa. There are villages where the adults are all blind and are led around by the children.

There is no vaccine or preventive medicine. DEET is used to control blackfly populations while people in risky areas wear pants and long sleeves.

Ivermectin in doses of 150µ per kg every six to twelve months provides treatment by slowly reducing the number of parasites in the skin and eyes, soothing inflammatory reactions and preventing disfigurement and blindness.

VisionConnection
http://www.visionconnection.org/Content/YourVision/EyeDisorders/ River+Blindess/default.htm?cookie%5Ftest=1

Centers for Disease Control
http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/default.htm

Sight Savers International
http://www.sightsavers.org/html/eyeconditions/river.htm

World Health Organization
http://www.who.int/pbd/blindness/onchocerciasis/en/