Current Course Topic:
River Blindness, or Onchocerciasis, is the world's second leading cause of blindness. Although rarely a life threatening disease, Onchocerciasis causes chronic suffering and severe disability among 18 million people worldwide, of whom 300,000 are irreversibly blind. The disease is mostly encountered in the Western and Central Africa, and to a lesser extent in the Middle East and the Americas.
Map showing where riverblindness is endemic.
Aside from being a leading cause of blindness, people suffering from River Blindness experience severe and continuous itching due to the presence of nodules that develop under the skin, causing them to scratch repeatedly. As a result, the damaged skin areas suffer a loss of pigmentation and, over the time, the skin becomes spotty, which causes de-pigmented spots that are more susceptible to skin cancer.
Onchocerciasis is a parasitic disease caused by a parasitic worm (Onchocerca volvulus) that can live in the human body for up to 14 years. The larval forms of these parasitic worms are introduced in the human body, as well as transmitted from a sick person to a healthy one, via the bite of infected blackflies (Simulium) that live and breed in fast flowing rivers because of their highly oxygenated water.
Once the thousands of microfilariae (microscopic larvae) produced by the female worm spread throughout the body and reach the eye they can cause a variety of conditions including serious visual impairment and blindness.
The whole cycle starts when, after mating, a parasitized female blackfly seeks a blood fest, which is necessary for the maturation of her eggs. Once the host's skin is stretched by the fly's apical teeth and the blood pumped up into the female blackfly, the fly's saliva passes into the host's skin, along with hundreds of Onchocerca larvae. The larvae migrate into the subcutaneous tissue to mature into adult worms, lodging in nodules and spreading throughout the body.
Each adult female worm (filaria), which can be more than half a meter in length, produces millions of microfilariae. After these microfilariae die, the host experiences extreme itchiness, severe rashes, skin depigmentation (the so called "leopard skin"_ and lymphadenitis (resulting in hanging groins and elephantiasis of the genitals). If the microfilariae reach the eye and eye, visual impairment and irreversible blindness results.
The normal method of diagnosis is to take a small skin snip and place it in a drop of saline. Within seconds, microfilariae can be seen leaving the skin.
The disease is treated with the drug Ivermectin, as a single dose to be taken annually. It controls the disease by killing the microfilariae. Nodulectomy (removal of nodules by surgery) is an important, although an expensive, adjunctive treatment.