Filariasis is a collective term for the parasitic
diseases caused by the roundworms called filariids, which constitute the superfamily Filariodea. The diseases are observed in all vertebrate groups except fish. Many infections are mild, producing no symptoms or minor dermatitis and inflammation. A few
Filariasis diseases in humans can be serious, although rarely fatal; in dogsÑand sometimes catsÑthe infestation known as heartworm, caused by Dirofilaria immitis, is often fatal (see dog; diseases, animal).
Human
filarial diseases are largely restricted to tropical and subtropical regions, where an estimated 140 million people are infected. They are transmitted from person to person by any of several genera of mosquitoes or other biting flies, which introduce the larval stage of the worm when taking a blood meal. The adult
worms live in various body tissues; the elongated embryos, called microfilariae, circulate in the bloodstream, where they frequently show a diurnal or nocturnal periodicity in their numbers.
The
Disease most commonly known as filariasis
occurs in Africa, Asia, and the South Pacific region. It is caused by Wuchereria bancrofti, Brugia malayi, and a few other roundworm species and is transmitted by mosquitoes. The adult worms live within the lymph ducts or glands, where they may eventually obstruct lymph circulation, leading to edema, or the abnormal accumulation of tissue fluid. The extremities and scrotum are most often affected and may swell to enormous proportions, a condition called elephantiasis; the skin over the swollen areas becomes dark, thick, and coarse. Another filarial disease, onchocerciasis (river blindness), causes serious skin disease and can lead to loss of vision if untreated; it occurs in Africa and Central and South America. African eye worm, Loa loa, is rarely serious.
Eradication of the mosquito vectors of the disease is the key to control of filariasis, but this has been difficult or impossible. The medical treatments available for filarial infections are largely unsatisfactory, but the World Health Organization is funding a major program to develop new drugs.
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