Bancroft's Filaria

(Wuchereria bancrofti), a parasitic roundworm of the family Filaria. Bancroft’s filaria parasitizes the lymph and blood vessels of man. The whitish or brown filamentous body is as long as 9 cm; males are smaller than females. The larvae emerge from the eggs in the lymph vessels and migrate to the blood vessels. They appear in the peripheral blood vessels only while the host sleeps. When the host awakes, the larvae withdraw to deeper-lying vessels. The larvae develop further for eight to 35 days in the stomach of mosquitoes that feed at night. Persons bitten by the insect become infected. The lymph vessels become dilated and inflamed; adjacent organs also become inflamed. Infestation may result in elephantiasis—the excessive growth of the hypodermic tissue of various organs (for example, the extremities). Bancroft’s filariae are most common in the tropics and subtropics.