Filariasis is a widespread infectious disease in the tropics caused by the parasite Wuchereria bancrofti which is transmitted by mosquitoes. The larvae move through the lymphatic vessels and into the lymph nodes where the worms mature (to adulthood). From there, the microfilaria disseminate into the blood.
Loiasis is also caused by microfilaria (Loa loa). However, Loiasis only exists in western and central Africa and can cause conjunctivitis (see image).
Infections of Wuchereria/Filaria bancrofti can evolve asymptomatically. However, fever states often exist in combination with headaches, muscle pains and lymphadenitis. Chronic infections can lead to lymph drain disorders with elephantiasis.
Detection of microfilaria in blood is diagnostic. The microfilaria are often found at the edge of blood film and can be more easily detected in a thick smear. Since the microfilaria from Wuchereria bancrofti is most active at night, blood samples taken at this time are more successful. Eosinophilia is nearly always present.