Lymphatic filariasis overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief:  Kalsang Dolma, M.B.B.S.[2]

## Overview

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Lymphatic filariasis, considered globally as a Neglected Tropical Disease, is a parasitic disease caused by microscopic, thread-like worms. The adult worms only live in the human lymph system. The lymph system maintains the body's fluid balance and fights infections. Lymphatic filariasis is spread from person to person by mosquitoes. People with the disease can suffer from lymphedema and elephantiasis and in men, swelling of the scrotum, called hydrocele. Lymphatic filariasis is a leading cause of permanent disability worldwide. Communities frequently shun and reject women and men disfigured by the disease. Affected people frequently are unable to work because of their disability, and this harms their families and their communities.

## Historical Perspective

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Lymphatic Filariasis is thought to have affected humans since approximately 1500-4000 years ago and the first documentation of symptoms occurred in the 16th century, when Jan Huygen Linschoten wrote about the disease during the exploration of Goa.

## Pathophysiology

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Infective larvae are transmitted by infected biting mosquitoes during a blood meal. The larvae migrate to lymphatic vessels and lymph nodes, where they develop into microfilariae-producing adults. The adults dwell in lymphatic vessels and lymph nodes where they can live for several years. The female worms produce microfilariae which circulate in the blood. The microfilariae infect biting mosquitoes. Inside the mosquito, the microfilariae develop in 1 to 2 weeks into infective filariform (third-stage) larvae. During a subsequent blood meal by the mosquito, the larvae infect the vertebrate host. They migrate to the lymphatic vessels and lymph nodes of the human host, where they develop into adults.

## Causes

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Lymphatic Filariasis is caused by nematodes (roundworms) that inhabit the lymphatic vessels and lymph nodes of a human host. Wuchereria bancrofti, Brugia malayi and Brugia timori cause lymphatic filariasis.

## Risk Factors

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Repeated mosquito bites over several months to years are needed to get lymphatic filariasis. People living for a long time in tropical or sub-tropical areas where the disease is common are at the greatest risk for infection. Short-term tourists have a very low risk.

## Diagnosis

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### History and Symptoms

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Most infected people are asymptomatic and will never develop clinical symptoms, despite the fact that the parasite damages the lymph system. A small percentage of persons will develop lymphedema. Filarial infection can also cause pulmonary tropical eosinophilia syndrome. Most people develop these clinical manifestations years after being infected.

### Other Diagnostic Studies

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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. The development of an immunochromatographic card test (ICT) with high sensitivity and specificity for detecting W. bancrofti infection has simplified diagnosis, and test kits are commercially available. The test requires 100 μl of fingerprick blood drawn at any time, day or night.

## Treatment

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### Medical Therapy

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People infected with adult worms can take a yearly dose of medicine, called diethylcarbamazine (DEC), that kills the microscopic worms circulating in the blood. While this drug does not kill all of the adult worms, it does prevent infected people from giving the disease to someone else. Lymphedema and elephantiasis are not indications for DEC treatment because most people with lymphedema are not actively infected with the filarial parasite. Physicians can obtain DEC from CDC after lab results confirm infection.

### Primary Prevention

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Avoidance of mosquito bites through personal protection measures or community-level vector control is the best option to prevent lymphatic filariasis. Periodic examination of blood for infection and initiation of recommended treatment are also likely to prevent clinical manifestations.

## Videos

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## References

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