Wuchereria bancrofti is a filarial (arthropod-borne) nematode (roundworm) that is the major cause of lymphatic filariasis. It is one of the three parasitic worms, together with Brugia malayi and B. timori, that infect the lymphatic system to cause lymphatic filariasis. These filarial worms are spread by a variety of mosquito vector species. W. bancrofti is the most prevalent of the three and affects over 120 million people, primarily in Central Africa and the Nile delta, South and Central America, the tropical regions of Asia including southern China, and the Pacific islands. If left untreated, the infection can develop into a chronic disease called lymphatic filariasis. In rare conditions, it also causes tropical eosinophilia, an asthmatic disease. No vaccine is commercially available, but high rates of cure have been achieved with various antifilarial regimens and lymphatic filariasis is the target of the WHO Global Program to Eliminate Lymphatic Filariasis with the aim to eradicate the disease as a public-health problem by 2020.