Filariasis clinic. Filariasis patient being examined at the Vector Control Research Centre in India. Filariasis is caused by parasitic worms spread by blood-sucking insects such as mosquitoes. 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 larvae of some species invade the eye, causing blindness. The spread of filariasis can be controlled using insecticides, mosquito nets and protective clothing.