Filariasis is caused by nematodes (roundworms) that inhabit the lymphatics and subcutaneous tissues. Three species cause lymphatic filariasis: Wuchereria bancrofti, Brugia malayi, and Brugia timori. Infection is transmitted by mosquito vectors; humans are definitive hosts. Lymphatic filariasis is a major cause of disfigurement and disability in endemic areas, leading to significant economic and psychosocial impact.
The diagnosis, treatment, and prevention of lymphatic filariasis will be reviewed here. The epidemiology, pathogenesis, and clinical features of lymphatic filariasis and other filarial infections, including onchocerciasis, loiasis, and mansonellosis, are discussed separately. (See "Epidemiology, pathogenesis, and clinical manifestations of lymphatic filariasis" and "Onchocerciasis" and "Loiasis (Loa loa infection)".)
A diagnosis of lymphatic filariasis should be considered in any patient with an appropriate exposure history who presents with characteristic signs and symptoms or unexplained eosinophilia. (See "Epidemiology, pathogenesis, and clinical manifestations of lymphatic filariasis".)
Definitive diagnosis can be made by detection of circulating filarial antigen (for W. bancrofti infection only), demonstration of microfilariae or filarial DNA in the blood, or of adult worms in the lymphatics. Rarely, microfilariae and/or adult worms are identified incidentally in tissue biopsies or cytological specimens . Peripheral blood eosinophilia is common and may exceed 3000/microL. The frequency of eosinophilia due to filariasis is difficult to determine since other helminth infections frequently coexist among individuals in endemic areas . Other nonspecific laboratory findings include elevated serum IgE, microscopic hematuria, and proteinuria. (See "Epidemiology, pathogenesis, and clinical manifestations of lymphatic filariasis", section on 'Renal involvement'.)
Circulating antigen detection — Circulating filarial antigen (CFA) assays have been developed for diagnosis of W. bancrofti infections but are not yet available for Brugian filariasis. These tests detect antigens released by adult filarial worms, so may be positive even in amicrofilaremic individuals . In addition, antigen levels remain stable during the day and night, so these tests can be performed at any time.