Brugia malayi. Light micrograph of many parasitic nematode worms (Brugia malayi), cause of human lymphatic filariasis (elephantiasis). The gut can be seen in these small transparent worms. Brugia malayi is one of five types of nematode worm which cause human filariasis. They are spread by blood- sucking insects. The worms then invade the human lymphatic system to produce thousands of larvae that spread around the body. Repeated infection causes lymph vessels to become inflamed and fluid to accumulate, which can lead to an enormous enlargement of parts of the body (elephantiasis). Treatment is usually with anthelmintic drugs. Magnification: x40 at 35mm size.