Filariae are parasitic, thread-like worms that live in the sub-cutaneous tissues (i.e. beneath the skin) and in the lymphatics (i.e. fluid surrounding various organs in the body).
Filariasis occurs mainly in the tropical regions (warm and moist) of the world. While the people living in these areas contract a milder form of this disease, those who travel to such places are prone to being affected by a more acute form.
Filarial worms usually cause skin diseases. Nine species of filaria cause diseases in humans. Four among these cause the most serious infections.