Filariasis is a disease associated with the infection of filariae within the definitive host, e.g. human host. It may be classified into three groups: (1) lymphatic filariasis, (2) subcutaneous filariasis, and (3) serous cavity filariasis.
In lymphatic filariasis, the filarial worms, such as Wuchereria bancrofti, Brugia malayi, and Brugia timori, occupy the lymphatic system of the definitive host. W. bancrofti is the most common causative agent of lymphatic filariasis. These filarial worms spread from one human host to another when mosquitoes carrying the larvae feed on blood of humans.
The disease may not manifest into symptoms. However, chronic cases that are left untreated may lead to the development of elephantiasis wherein the skin becomes enormously thickened, and is rough, hard, and fissured, like an elephants hide. The lower extremities are often the parts affected by elephantiasis. Other parts affected though not as common are breasts, arms, scrotum, and vulva. The disease is most common in Africa and Asia.