Quick Facts
filariasis leg 200x300Patient with elephantiasis of left leg. Credit: WHO/TDR/Chandran

Lymphatic filariasis is caused by infection with a parasitic round worm transmitted by the bite of certain mosquitoes. The disease leads to the painful, disfiguring and psychologically damaging condition known as elephantiasis. Not only do those infected have grossly enlarged arms and legs, but they can incur disabling kidney and lymphatic damage. Lymphatic filariasis affects over 120 million people in 73 countries throughout tropics and sub-tropics of Asia, Africa, the Western Pacific, and parts of the Caribbean and South America.

What is it?

Lymphatic filariasis is caused by the filarial nematode parasites (parasitic round worms): Brugia malayi, Brugia timori and Wuchereria bancrofti, which are transmitted by several species of mosquitoes. When an infected mosquito bites a human to take a blood meal, infectious larvae enter the skin. Worms migrate to the lymphatic system, and females produce microfilariae (very young larvae) which migrate back to the blood stream. When a mosquito takes a blood meal, microfilariae are ingested and develop into infectious larvae to continue the lifecycle.

The adult worms in the lymphatic system contain symbiotic bacteria. These bacteria can cause a strong immune reaction that leads to the obstruction of lymph vessels and extreme swelling of the extremities, called elephantiasis. Elephantiasis is painful, disfiguring and both physically and psychologically damaging. Chronic infection leads to disabling kidney and lymphatic damage even without manifestation of elephantiasis.

Although current treatments such as ivermectin can reduce transmission of the parasite by killing the microfilariae, adult worms are not affected. Thus infected people, even though treated, are not cured of disease. There is no vaccine available for this infection and more effective therapeutics are urgently needed.b malayi cdc

Where does it occur?

filaria teal 320x169Over 1 billion people are at risk of infection with the worm that causes lymphatic filariasis (elephantitis), and approximately 120 million people are currently infected; of these almost 40 million have disfigurement from this disease. Approximately 66% of those at risk live in Africa, while 33% are in India, Indonesia, Malaysia, Philippines, and Pacific islands.