Guidance for Evaluation and Treatment

Diagnosis

The standard method for diagnosing active infection is the identification of microfilariae in a blood smear by microscopic examination. Microfilariae can be detected microscopically on blood smears obtained at night (10 PM–2 AM) and 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 US Food and Drug Administration.

Other methods of diagnosis include: tissue specimens to visualize adult worms or microfilariae as well as ultrasonography which allows visualization of adult worms (ultrasonography demonstration can be found at http://www.filariajournal.com/content/2/1/3).

For questions regarding diagnostic considerations, contact the Division of Parasitic Diseases (404-718-4745), email: parasites@cdc.gov

More on: Diagnostic Procedures [DPDx]

Antiparasitic Treatment

The main goal of treatment of an infected person is to kill the adult worm. Diethylcarbamazine citrate (DEC), which is both microfilaricidal and active against the adult worm, is the drug of choice for lymphatic filariasis. The late phase of chronic disease is not affected by chemotherapy. Ivermectin is effective against the microfilariae of W. bancrofti, but has no effect on the adult parasite.

Because lymphatic filariasis is rare in the U.S., DEC is no longer approved by the Food and Drug Administration (FDA) and cannot be sold in the U.S. Physicians can obtain the medication from CDC after confirmed positive lab results. Call: 404-718-4745. Treatment of lymphatic filariasis in adults and children ≥ 18 months of age involves either a 1-day or 12-day treatment course (6 mg/kg/day). One day treatment is generally as effective as the 12-day regimen. For tropical pulmonary eosinophilia (TPE), a longer DEC treatment course of 14-21 days is generally recommended. DEC is generally well tolerated. Side effects are generally limited and depend on the number of microfilariae in the blood. The most common side effects are dizziness, nausea, fever, headache, or pain in muscles or joints.

DEC is contraindicated in patients who may also have onchocerciasis. Prior to DEC treatment for lymphatic filariasis, onchocerciasis should be excluded in all patients with a consistent exposure history due to 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 microfilarial levels > 2,500/mm3 due to the potential for life-threatening side effects, including encephalopathy and renal failure. Neither steroids pre-treatment nor slow dose escalation prevents these complications. Consultation with a tropical medicine specialist is recommended in these scenarios.  
The drug ivermectin kills only the microfilariae, but not the adult worm; the adult worm is responsible for the pathology of lymphedema and hydrocele.
Some studies have shown adult worm killing with treatment with doxycycline (200mg/day for 4–6 weeks).