Elephantiasis. Grossly swollen legs in a patient with lymphatic filariasis. This disease is caused by parasitic nemotode worms transmitted in larval form by the bite of mosquitoes. The larvae develop into adult worms (macrofilariae) that lodge in the lymphatic system. The lymphatic system circulates the lymph fluid, and the worms block the lymph vessels and cause this fluid to accumulate in the limbs, a condition known as lymphoedema, and more commonly called elephantiasis. The condition is rarely fatal, but causes widespread suffering in tropical regions. Treatment involves drug therapy and rigorous hygiene to prevent skin infections. Photographed in Haiti.