Filarial worm infections overview

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Filarial worm infections are caused by certain roundworms and affect different parts of the body depending on the species of worm.
There are many species of filarial worms, but only a few infect people. Species that infect people may reside in

Tissues under the skin (subcutaneous tissues) or in the eye: African eye worm (Loa loa), which causes loiasis, or Onchocerca volvulus, which causes river blindness (onchocerciasis)
Lymph tissues: Wuchereria bancrofti, Brugia malayi, or Brugia timori, which cause lymphatic filariasis

Most filarial infections occur in tropical and subtropical areas.
Infection with the dog heartworm (Dirofilaria immitis) occurs worldwide, including in North America. This infection rarely causes symptoms, because the dog heartworm does not develop to maturity in people. But on occasion an immature heartworm reaches the lungs and may cause chest pain and cough. Very rarely, larvae form nodules in the eyes, brain, and/or testes.
(See also Overview of Parasitic Infections.)