Filariasis is a disease associated with the infection of filariae within the definitive host, e.g. human host. It may be classified into three groups: (1) lymphatic filariasis, (2) subcutaneous filariasis, and (3) serous cavity filariasis.
In subcutaneous filariasis, the filariasis is caused by parasitic roundworms that occupy the subcutaneous layer of the skin (fat layer).
The roundworms that have been associated with subcutaneous filariasis are Loa loa, Mansonella streptocerca, and Onchocerca volvulus.
Loa loa (also called eye worm) is a filarial nematode common in Africa and India. Its larvae use horseflies (Chrysops) as intermediate hosts. These insects transmit the worm to a definitive host, e.g. humans, by insect bite. Filariasis caused particularly by Loa loa is called loiasis or Loa loa filariasis.
Mansonella streptocerca is mostly found in West and Central Africa. Its intermediate host is a midge insect (Culicoides sp.). The definitive hosts are humans and chimpanzees.
Onchocerca volvulus is a filarial nematode that can cause river blindness (onchocerciasis) and is found mostly in Africa. The intermediate host of this worm is the black fly. The only known definitive host is humans. Infestation with this worm results in blindness when the corneal stroma thickens due to chronic corneal inflammation.