Management of Filariasis

• Onchocerciasis (River blindness)
• Lymphatic filariasis (Elephantiasis)
• Loiasis (Loa loa infection)

All are caused by parasitic filarial nematode worms that are transmitted between humans by blood-sucking insects.

• Onchocerciasis is caused by Onchocerca volvulus, transmitted by the bite of an infected female blackfly
• Lymphatic filariasis is caused by Wuchereria bancrofti (90% of cases), Brugia malayi (most of the remainder) and Brugia timori, and is transmitted by various mosquito species
• Loa loa worms are transmitted by the bites of Mango flies or by Deer flies (Chrysops spp.).

Lymphatic filariasis

• Lymphatic filariasis is caused by three thread-like parasitic worms, called filariae. The species Wuchereria bancrofti is the most prevalent worldwide, Brugia malayi is found mostly in eastern Asia, and B. timori is confined to East Timor and adjacent islands.
• Filarial parasites in their adult stage live in the lymphatic system.
• The worms have an estimated active reproductive span of 4–6 years, producing millions of small immature larvae, microfilariae, which circulate in the peripheral blood.

Diagnosis

• The standard method for diagnosing active infection is the identification of microfilariae in a blood smear by microscopic examination.
• The microfilariae that cause lymphatic filariasis circulate in the blood at night (called nocturnal periodicity). Blood collection should be done at night to coincide with the appearance of the microfilariae, and a thick smear should be made and stained with Giemsa or hematoxylin and eosin.
• For increased sensitivity, concentration techniques can be used.
• Serologic techniques 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.
• Because lymphedema may develop many years after infection, lab tests are most likely to be negative with these patients.

Goal of treatment

• The main goal of treatment of an infected person is to kill the adult worm.

Choice of medications

Diethylcarbamazine citrate (DEC)

• Have 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

• Effective against the microfilariae of W. bancrofti, but has no effect on the adult parasite.

Albendazole

• No direct effect on microfilariae but leads to a slow decline in microfilaremia due to macrofilaricidal activity against the adult worms. Albendazole can be used in patients with concomitant loiasis or onchocerciasis.

Treatment

• All people with filariasis who are positive in the immunochromatographic test or have microfilaraemia should receive anti-filarial drug treatment to eliminate microfilariae (and adult worms when diethylcarbamazine is used)

• They can be treated with one of the following regimens:

(i) a single dose of a combination of albendazole (400 mg) with ivermectin (150–200 μg/kg) in areas where onchocerciasis is co-endemic

(ii) a single dose of a combination albendazole (400 mg) plus diethylcarbamazine (6 mg/kg)
or
(iii) diethylcarbamazine 6 mg/kg alone for 12 days in areas where onchocerciasis is non co-endemic

For tropical pulmonary eosinophilia (TPE), a longer DEC treatment course of 14-21 days is generally recommended. DEC is generally well tolerated.

Diethycarbamazine precaution

• DEC is contraindicated in patients who may also have onchocerciasis due to the possibility of severe exacerbations of skin and eye involvement.
• 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.

References

1. https://www.cdc.gov/parasites/lymphaticfilariasis/health_professionals/dxtx.html

2. https://www.uptodate.com.ezp.imu.edu.my/contents/diagnosis-treatment-and-prevention-of-lymphatic-filariasis

3. World helath Organization Global Programme To Eliminate Lymphatic Filariasis, 2013