The most common type of filariasis is infection with a parasitic worm that lives in the human lymph system. This is called lymphatic filariasis. Lymphatic filariasis is a disease of the tropics. Wuchereria bancrofti , the most common filariasis parasite, is found in Africa, India, Southeast Asia, the Pacific islands, the Caribbean, and South America. The Brugia malayi and Brugia timori parasites are found in Southeast Asia.
Filariasis is spread from infected persons to uninfected persons by mosquitoes.
Adult worms live in an infected person's lymph vessels. The females release large numbers of very small worm larvae, which circulate in an infected person's bloodstream. When the person is bitten by a mosquito, the mosquito can ingest the larvae. These develop in the mosquito and can then be spread to other people via mosquito bites. After a bite, the larvae pass through the skin, travel to the lymph vessels, and develop into adults, which live about 7 years.