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Cutaneous filariasis 

Cutaneous filariasis

Chapter:
Cutaneous filariasis
Author(s):

Gilbert Burnham

DOI:
10.1093/med/9780199204854.003.070901_update_001

Update:

Treatment/prevention—impact of mass distribution of ivermectin.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 26 March 2017

Filarial infections are transmitted by simulium flies, some of which bite humans almost exclusively, whereas others are to varying degrees zoophilic. They are found worldwide in humans and animals, the filariae which cause cutaneous infections being Onchocerca volvulus, Loa loa, and the mansonellas.

Onchocerciasis

Onchocerciasis (river blindness), caused by O. volvulus, infects perhaps 20 million people, mostly in Africa.

Clinical features—larvae introduced into the body when the vector takes a blood meal develop into male or female adult worms within palpable nodules, commonly located over bony prominences. Other important manifestations are: (1) Eye damage—microfilariae enter the cornea from the skin and conjunctiva; manifestations include sclerosing keratitis, iridocyclitis and (sometimes) choroidoretinal lesions; without treatment permanent visual impairment or blindness are common. (2) Skin disease—ranging from itching with a localized maculopapular rash, to intensely itching with a chronic generalised papular rash or lichenified hyperkeratotic lesions.

Diagnosis, treatment, and prevention—diagnosis is usually made by finding microfilariae in skin snips. Treatment is with ivermectin, often given as a single annual dose, which has dramatically reduced the eye and skin lesions that ravaged many communities in Africa and Latin America. Methods of prevention include adding insecticides to rivers to interrupt simulium breeding and mass distribution of ivermectin.

Loa loa

This filaria, for which humans are the only host, is transmitted by the chrysops fly in West and Central Africa. Clinical manifestations include transient localized inflammatory oedema (Calabar swellings), the appearance of a migrating worm under the skin or (most dramatically) crossing the eye, and (rarely) meningoencephalitis. Diagnosis is based on typical clinical findings, or traditionally by finding microfilariae in a daytime blood sample. Treatment is usually with diethylcarbamazine, although both ivermectin and albendazole are effective. All treatments risk serious adverse reactions in the heavily affected. The best prevention is avoiding chrysops fly bites.

Mansonellas

This group of filarial infections is transmitted by culicoides midges and is common to many countries, but of negligible clinical importance under most circumstances. Only Mansonella streptocerca produces clear-cut manifestations, most typically chronic papular skin lesions. Diagnosis is by finding characteristic microfilariae in the blood or skin. People who are asymptomatic do not require treatment, but M. streptocerca responds well to ivermectin.

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