LF is caused by the infection by a nematode worm, Wuchereria bancrofti, which has a nocturnal periodicity of its microfilaria (infectious larvae) occurring in peripheral blood, which coincides well with the biting periodicity of mosquitoes such as Culex quinquefasciatus. The adult parasites occur in lymphatic vessels of man, while female worms produce larvae of the parasite. The mosquitoes on taking a blood meal become infected; larvae develop in the thoracic muscles of the mosquito, mature and migrate as infective stage larvae into the mouthparts of the mosquito and enter the broken skin of the human host, when the mosquito takes a blood meal, and the LF transmission cycle is completed.
LF infection may present in human beings with symptoms which range from recurrent fever in the acute phase to chronic features such as swellings in legs (big foot), breasts and the genitalia. To some extent, this disease may be quite disabling. However, in the early stages of the infection, patients with microfilaria (mf) in peripheral blood (infectious) may be asymptomatic.