Onchocerciasis is common in areas where specific types of blackflies (genus simullum) breed. Usually the best breeding grounds are fast-flowing rivers and streams. The blackfly spreads the disease in the following manner.The blackfly bites a person who is infected with onchocerciasis.The larvae of the parasite are taken from the skin of the person and pass with the tissue juices into the blackfly.In the fly, the larvae become infective in about six to ten days. When the fly bites again the larvae pass from the fly into the person.Lumps form under the skin. These nodules contain adult round worms which produce large numbers of larvae that live in the skin waiting to be sucked up by a blackfly.

Of the millions of larvae, only a few are taken in by blackflies. The rest wander through the host's tissues until they die in the human body. The body tries to fight the effects of the dead larvae by building scar tissue around them. These scars form in the body. Many larvae die in the lens and other parts of the eye. Eventually, the lens becomes so full of scar tissue that the person becomes blind.The nodules containing the adult worms are not always easy to detect because they may be deep in the body. Generally the presence of nodules, patches on the skin and itchiness are symptoms of onchocerciasis.

Geographic Distribution

Geographical distribution in the Western hemisphere

Is limited to Guatemala, southern Mexico, northern Venezuela, Colombia and Brazil. In Africa it is mainly found south of the Sahara, in an area extending from Senegal to Ethiopia, down to Angola in the west and Tanzania in the east. One of the largest endemic areas occurs in the Volta River basin area, which incorporates Benin, Ghana, Ivory Coast, Mall, Niger, Togo and all of Burkina Faso.

Clinical Picture

Onchocerciasis is recognized by an intense itchy rash, altered pigmentation, swelling and vesting of the skin and some systemic effects. The most important lesions are those of the eye, which lead to serious loss of vision and blindness.

With kind regards

Sophia

Managing Editor

Journal of Community Medicine & Health Education