Wuchereria bancrofti. Computer illustration of the microfilaria larval stage of the parasitic worm Wuchereria bancrofti, which causes filariasis in humans. W. bancrofti larvae are also found in several mosquito hosts. They enter the human body as the mosquitoes feed, and migrate to the lymphatic system, where they mature. The adult female produces thousands of microfilariae, which enter the circulation and are ingested by feeding mosquitoes. Adult worms can block the lymph vessels, causing thickening and enlargement of infected tissues. Other symptoms include fever and swelling of the lymph nodes. Illustration shows diagnostic morphological features of W. bancrofti, it is sheathed, without nuclei in the tip of the tail.