Epidemiology, pathogenesis, and clinical manifestations of lymphatic filariasis
- Amy D Klion, MD
Amy D Klion, MD
- Baltimore, MD
Filariasis is caused by nematodes (roundworms) that inhabit the lymphatics and subcutaneous tissues. Three filarial species cause lymphatic filariasis: Wuchereria bancrofti, Brugia malayi, and Brugia timori. Infections are 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 epidemiology, pathogenesis, and clinical features of lymphatic filariasis will be reviewed here. The diagnosis, treatment, and prevention of lymphatic filariasis and other filarial infections, including onchocerciasis, loiasis, and mansonellosis, are discussed separately. (See "Diagnosis, treatment, and prevention of lymphatic filariasis" and "Onchocerciasis" and "Loiasis (Loa loa infection)".)
W. bancrofti occurs in sub-Saharan Africa, Southeast Asia, the Indian subcontinent, many of the Pacific islands, and focal areas of Latin America and the Caribbean (including Haiti). B. malayi occurs mainly in China, India, Malaysia, the Philippines, Indonesia, and various Pacific islands. B. timori occurs on the Timor Island of Indonesia (figure 1). Overall, approximately two-thirds of individuals infected with lymphatic filariasis are in Asia. The epidemiology of lymphatic filariasis is changing due to implementation of a global program of mass drug administration (MDA) to eliminate transmission. Not only has mapping of disease prevalence prior to MDA led to reclassification of some countries (Costa Rica, Suriname, Trinidad and Tobago) as nonendemic, but some countries, including Togo, Vietnam, Cambodia, American Samoa, the Cook Islands, the Marshall Islands, Tonga, and Vanuatu, appear to have eliminated transmission entirely .
It is estimated that more than 120 million people worldwide are infected. More than 90 percent of these infections are due to W. bancrofti, while the remainder is due largely to B. malayi. Estimates suggest that more than 40 million infected individuals are seriously incapacitated and disfigured by lymphatic filariasis . One study in India noted that patients with chronic filariasis lose around 29 days of work per year due to complications of infection, highlighting the considerable burden the disease places on individuals and on the community . Another study reported an estimated productivity loss due to lymphatic filariasis of 77 to 100 percent during attacks of acute dermatolymphangioadenitis, 10 to 26 percent for lymphedema, and 15 to 19 percent for hydrocele . In addition, data suggest that the prevalence of depressive illness is high, accounting for an estimated 5.09 million disability-adjusted life years (DALYs) .
Lymphatic filariasis is likely first acquired in childhood; it has been suggested that as many as one-third of children are asymptomatically infected before age five . The risk of infection in childhood may be related to the maternal immune response during pregnancy. In one study of 159 Kenyan pregnant women with active Wuchereria infection, neonates lacking filarial-specific T cell responses in cord blood at birth had a 13-fold increased risk of developing childhood infection (compared with uninfected controls) .
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- Life cycle
- Host immune response
- CLINICAL MANIFESTATIONS
- Acute manifestations
- - Acute adenolymphangitis (ADL)
- - Acute dermatolymphangioadenitis (DLA)
- Filarial fever
- Tropical pulmonary eosinophilia
- Chronic manifestations
- - Lymphedema
- - Renal involvement
- Travelers and expatriates