@tasa good question.
Elephantiasis is caused by a parasite called a filarial worm. Elephantiasis is simply a condition where the vessels that bring fluid to the legs swell and increase especially the legs. These vessels are called lymphatic vessels and carry a fluid called lymph. That is why it is also commonly referred to as lymphatic filariasis. This disease is a good example of a disease transmitted from one person to the other by a mosquito. Also called vector-borne disease.