Filariasis risk. A young boy washing at a weed- filled canal in India. This canal is an ideal habitat for mosquitoes which transmit lymphatic filariasis. Filariasis is caused by parasitic worms spread by various blood-sucking insects. The worms invade the lymphatic system producing thousands of larvae that spread around the body. Repeated infection causes inflammation of lymph vessels and accumulation of fluid, which can lead to enormous enlargement of parts of the body (elephantiasis). The spread of filariasis can be controlled using insecticides and protective clothing, and by avoiding mosquito-ridden areas.