Scrotal elephantiasis, historical image. Elephantiasis, also known as lymphatic filariasis, is caused by parasitic nemotode worms transmitted in larval form by the bite of mosquitoes. The larvae develop into adult worms (macrofilariae) that lodge in and block the lymphatic system. This causes lymph to accumulate in the limbs (or here, in the scrotum), a form of lymphoedema. Elephantiasis is rarely fatal, but causes widespread suffering in tropical regions.