Clinical Overview of Lymphatic Filariasis

At a glance

Clinical expression of lymphatic filariasis varies considerably. Adult filarial worms commonly cause subclinical lymphatic dilatation and dysfunction. Blood smears and serologic tests are typically used for diagnosis.

Community health worker takes blood sample via fingerstick from man while children watch on.


Lymphatic filariasis can be caused by three species of mosquito-borne filarial nematodes: Wuchereria bancrofti, Brugia malayi, and B. timori. However, about 90% of cases are caused by W. bancrofti, also known as Bancroftian filariasis.

Clinical features

The clinical expression of lymphatic filariasis varies considerably. Most infected persons are asymptomatic. Even in asymptomatic people, adult filarial worms commonly cause subclinical lymphatic dilatation and dysfunction.

Filarial lymphadenopathy is seen commonly in infected children; before puberty, adult worms can be detected by ultrasonography of the inguinal, crural, and axillary lymph nodes and vessels. Death of the adult worm triggers an acute inflammatory response, which progresses distally (retrograde) along the affected lymphatic vessel, usually in the limbs and is termed acute filarial lymphangitis. If present, systemic symptoms, such as headache or fever, are generally mild.

In postpubertal males, adult W. bancrofti organisms are found most commonly in the intrascrotal lymphatic vessels and can be visualized on ultrasound examination. Inflammation resulting from adult worm death, in this area, may present as funiculitis, epididymitis, or orchitis. A tender granulomatous nodule may be palpable at the site of the dead adult worms.


The chronic manifestations of lymphedema and/or hydrocele will develop in approximately 30% of people infected. Lymphedema mostly affects the legs, but can also occur in the arms, breasts, and genitalia. Most people develop these symptoms years after the initial infection has cleared.

Filarial hydrocele is thought to be the consequence of lymphatic damage caused by adult worms. Chyluria, which results from rupture of dilated lymphatics into the renal pelvis, can occur as a manifestation of bancroftian filariasis. Microscopic hematuria and proteinuria are also found in lymphatic filariasis patients.

Recurrent secondary bacterial infections of the affected extremity, characterized by severe pain, fever and chills, hasten the progression of lymphedema to its advanced stage, known as elephantiasis.

Another complication of lymphatic filariasis is tropical pulmonary eosinophilia (TPE) syndrome, a potentially serious, progressive lung disease characterized by fever and non-productive, nocturnal cough, wheezing, or both. Symptoms result from immune hyper-responsiveness to microfilariae in the pulmonary capillaries. Signs include marked eosinophilia, high serum immunoglobulin E concentrations, and positive antifilarial antibodies. Peripheral microfilaremia is absent in patients with TPE. Most cases of TPE have been reported in long-term residents from Asia, with men ages 20 – 40 most commonly affected.


The standard method for definitive diagnosis of active infection is the identification of microfilariae in a blood smear by microscopic examination. Microfilariae can be detected microscopically on blood smears obtained at the time of peak microfilariae circulation (most often at night (10 PM – 2 AM). A thick smear should be made and stained with Giemsa or hematoxylin and eosin. For increased sensitivity, concentration techniques can be used.

Serologic enzyme immunoassay tests, including antifilarial IgG1 and IgG4, provide an alternative to microscopic detection of microfilariae for the diagnosis of lymphatic filariasis. Patients with active filarial infection typically have elevated levels of antifilarial IgG4 in the blood and these can be detected using routine assays.

Assays for circulating parasite antigen of W. bancrofti are not presently approved by the U.S. Food and Drug Administration. There are no antigen test for Brugia spp.

Other methods of diagnosis include

  • Tissue specimens to visualize adult worms or microfilariae.
  • Ultrasonography, which allows visualization of adult worms.

For questions regarding diagnostic or treatment considerations, contact the Division of Parasitic Diseases and Malaria Diagnostic assistance is also available via DPDx.