Lymphatic filariasis, also known as elephantiasis, is best known from dramatic photos of people with grossly enlarged or swollen arms and legs. The disease is caused by parasitic worms, including Wuchereria bancrofti, Brugia malayi, and B. timori, all transmitted by mosquitoes. Lymphatic filariasis currently affects 120 million people worldwide, and 40 million of these people have serious disease.

When an infected female mosquito bites a person, she may inject the worm larvae, called microfilariae, into the blood. The microfilariae reproduce and spread throughout the bloodstream, where they can live for many years. Often disease symptoms do not appear until years after infection. As the parasites accumulate in the blood vessels, they can restrict circulation and cause fluid to build up in surrounding tissues. The most common, visible signs of infection are excessively enlarged arms, legs, genitalia, and breasts.

Medicines to treat lymphatic filariasis are most effective when used soon after infection, but they do have some toxic side effects. In addition, the disease is difficult to detect early. Therefore, improved treatments and laboratory tests are needed. A vaccine is not yet available.