Clinical Manifestations Diagnosis and Treatment

O. volvulus, one of several filarial worms that are important human parasites, lives in the cutaneous and subcutaneous tissues. Humans are the only definitive host; there is no animal reservoir. Numbers of adult worms, the females of which may reach a length of 50 centimeters, live in large coiled masses, which usually become surrounded by fibrotic tissue generated by the host. In these nodules, which may reach the size of a walnut and are often easily visible on the head, trunk, hips, or legs, the adults can live and breed for as long as 16 years. Thousands of larvae, the microfilariae, emerge from the nodules and migrate in the tissues of the skin. Host immune reactions to dead or dying microfilariae cause various forms of dermatologic destruction, including loss of elasticity, depigmentation, and thickening of the skin. These changes are complicated by the host's reaction to the extreme pruritis caused by the allergic reactions to the worm proteins; the victim may scratch him- or herself incessantly in a vain attempt to relieve the tormenting itch. This condition is sometimes called "craw-craw" in West Africa. Wandering microfilariae can also cause damage to the lymphatic system and inguinal swellings known as "hanging groin." Microfilariae that reach the eye cause the most damage. Larvae dying in various ocular tissues cause cumulative lesions that, over a period of one to several years, can lead to progressive loss of sight and total blindness. There appear to be distinct geographic strains, which help to explain different pathological pictures in parts of the parasite's range; for example, in forest regions of Cameroon a smaller percentage of infected persons experience ocular complications than do inhabitants of the savanna.

Diagnosis is by detection of nodules, by microscopic demonstration of microfilariae in skin snips, and, in recent years, by a number of immunologic tests. Therapy includes surgical removal of nodules, which has been widely practiced in Latin America to combat eye damage, and various drugs to kill the wandering microfilariae. The first drug to be widely used was diethylcarbamiazine (DEC), but in heavily infected people it may cause serious side effects when the immune system reacts to the allergens released by large numbers of dying worms. Dermato-logic complications of DEC can be severe, but these are treatable with antihistamines and corticosteroids; ophthalmologic complications are less common but more dangerous. Suramin, a drug used to combat trypanosomiasis, is effective against both microfilariae and adult worms, but it has serious side effects and, like DEC, is too dangerous to use in mass campaigns. Some success has been reported with antihelminthics like mebendazole, but only ivermectin, a microfilaricide introduced in the early 1980s, seems safe and effective enough for widespread use in rural areas of developing countries.

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