Lymph node with filaria worms, illustration. Filaria are parasitic nematode worms transmitted in larval form by the bite of mosquitoes, they cause elephantiasis, also known as lymphatic filariasis. The larvae develop into adult worms (macrofilariae) that lodge in and block the lymphatic system, which is shown in the image. This causes lymph fluid to accumulate in the limbs, a form of lymphoedema. Elephantiasis is rarely fatal, but causes widespread suffering in tropical regions. Treatment involves drug therapy and rigorous hygiene to prevent skin infections.