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Filariasis

12 June 2012, by DEVELOUX M.

1 - LYMPHATIC FILARIASIS

Lymphatic filariasis is a helminthiasis transmitted by mosquitoes belonging to several genera. These are tropical diseases whose chronic manifestations result from obstruction of the lymph ducts by adult filariae [1].

An estimated 120 million people are infected worldwide. Wuchereria bancrofti and its pacifica variety is the most common species and is found throughout the intertropical zone. Brugia malayi, is the second most common species and is only found in certain regions of South Asia. Brugia timori is restricted to certain Indonesian islands. It is a rarely notified imported parasitosis in Metropolitan France. It is no longer reported in France’s overseas departments or territories with the exception of Mayotte and certain islands of French Polynesia where it is still hypoendemic.

The adult filariae measuring 4 to 8 cm long live in the lymphatic ducts. Microfilariae, or the embryos emitted by the female worms, pass into the bloodstream with a periodicity that varies from species to species and strain to strain. W. bancrofti is mainly nocturnal. The vectors are female mosquitoes of the Culex, Aedes, Anopheles and Mansonia genera. The microfilariae are absorbed by a vector during a blood-meal taken from an infected human. Inside the mosquito vector or intermediate host, the microfilariae mature into motile larvae which are then egested into a human host’s blood when the mosquito has its next blood-meal.

The clinical manifestations become apparent after an incubation period carrying from a few months to several years. In man, W. bancrofti frequently causes genital symptoms including lymphangitis of the scrotum, orchitis and vaginal hydrocele. Limb lymphangitis progresses centrifugally. Adenitis may be seen alone or with lymphangitis. After one or more years of repeated episodes, the lymphatic ducts become blocked, giving rise to the clinical signs of the disease. Sometimes spectacular, these signs have become increasingly rare as patients now receive prompt treatment. The disorder affects the genitals and lymphatic system, causing hydroceles, orchi-epididyimitis, adenopathies, adenolymphoceles and superficial or deep lymph varices, of which elephantiasis is the most common manifestation. Filarian elephantiasis particularly affects the leg and foot. The skin is lumpy, irregular and vegetant. It is to be distinguished from streptococcal elephantiasis, diffuse lymphangiomas, Kaposi’s disease or chromoblastomycosis. Filarian elephantiasis may also spread to the arm, scrotum, vulva and breast.

A non-negligible proportion of infected subjects remain asymptomatic.

The diagnosis is confirmed by the detection of microfilariae in the blood. The time the sample is obtained must take into account the periodicity of the species. Several methods with varying sensitivity can be used to detect microfilariae. These include smears, thick smears, the leukoconcentration test and membrane filtration. The blood eosinophilia is only present at the early phase of the infection. The serology is non specific and the test is often negative by the time the disease becomes clinically manifest.

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