Lymphatic filariasis or elephantiasis is infectious disorders caused by threadlike worms (filariae). Spread by blood-sucking mosquitoes, the infective larvae take about a year to develop inside humans into adult worms. They live in the lymph glands and lymphatic vessels, especially those draining the genital area and legs. Untreated, this disease can cause massive swelling of the legs called elephantiasis because the leg of an affected person can resemble an elephant's leg. In men it can also cause a large collection of fluid (a hydrocele), in the scrotum. The adult worms also cause allergic reactions and give birth to embryos which migrate to near the skin. From there they pass into mosquitoes mixed up with their bloody meal.
Prevention is by avoiding being bitten by, and by eradicating the mosquitoe carriers.
Lymphatic filariasis caused only 0.0007% of all deaths worldwide in 2002 or an average of 1 death per 10 million people, but is included here because of the chronic disability it causes.