Filarial nematodes Wuchereria bancrofti, Brugia malayi , and B. timori .
Through the bite of infected Aedes, Culex, Anopheles , or Mansonia mosquitoes.
Found in sub-Saharan Africa, Egypt, southern Asia, the western Pacific Islands, the northeastern coast of Brazil, Guyana, Haiti, and the Dominican Republic. Travelers are at low risk, although infection has been documented in long-term travelers. Most infections in the United States are seen in immigrants and refugees.
Most infections are asymptomatic, but lymphatic dysfunction may lead to lymphedema of the leg, scrotum, penis, arm, or breast years after infection. Acute episodes of recurrent secondary infections in people with lymphatic dysfunction characterized by painful swelling of an affected limb, fever, or chills hasten the progression of lymphedema to its advanced stage, known as elephantiasis. Tropical pulmonary eosinophilia (TPE) syndrome is a potentially serious progressive lung disease that presents with nocturnal cough, wheezing, and fever, resulting from immune hyperresponsiveness to microfilariae in the pulmonary capillaries. Most cases of TPE have been reported in long-term residents from Asia. Men aged 20–40 years are most commonly affected.
Microscopic detection of microfilariae on an appropriately timed thick blood film. Determination of serum antifilarial IgG is also a diagnostically useful test, especially when microfilariae are not identifiable. This assay is available through the National Institutes of Health (301-496-5398) or through CDC (www.cdc.gov/dpdx; 404-718-4745; email@example.com). Microfilariae are usually not detected in patients with tropical pulmonary eosinophilia. Diagnosis requires epidemiologic risk and filarial antibody testing.
The drug of choice, diethylcarbamazine (DEC), can be obtained from CDC under an investigational new drug protocol. DEC is contraindicated in patients who may also have onchocerciasis. Before DEC treatment for lymphatic filariasis, onchocerciasis should be excluded in all patients with a consistent exposure history because of the possibility of severe exacerbations of skin and eye involvement (Mazzotti reaction). In addition, DEC should be used with extreme caution in patients with circulating Loa loa microfilaria because of the potential for life-threatening side effects. Patients with lymphedema and hydrocele can benefit from lymphedema management and, in the case of hydrocele, surgical repair. There is evidence that a 4–8-week course of doxycycline (200 mg daily) can both sterilize adult worms and improve lymphatic pathologic features.
Mosquito precautions (see Chapter 3, Mosquitoes, Ticks & Other Arthropods).
CDC website: www.cdc.gov/parasites/lymphaticfilariasis
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Christine Dubray, Sharon L. Roy