An infection of the lymph system by a parasite called a filarial worm.

Lymphatic filariasis is caused by parasites that are spread between people by mosquitoes. The parasites travel to the lymph system and stay there as adult worms. Worms at other stages of life are found in the blood of a person with lymphatic filariasis.

Lymphatic filariasis may not have any symptoms. Rarely, long-term damage to the lymph system causes swelling in the legs, arms and genitals. It also increases the risk of frequent bacterial infections that harden and thicken the skin. This skin change is sometimes called elephantiasis.

Lymphatic filariasis is treated with medicine that targets the worms in blood. It's taken once a year. Damage caused by adult worms can be treated by healthcare professionals who specialize in the lymph system.