Filarial worm infections are caused by certain roundworms (nematodes) and affect different parts of the body depending on the species of worm.
Helminths are parasitic worms that can infect humans and animals. There are 3 types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes). Filarial worms are roundworms.
A main difference between filarial worms and other roundworms is that they are transmitted to people via the bites of infected insects, such as blackflies, deerflies, and mosquitoes. Roundworms that are not filarial, such as pinworms and hookworms, are usually transmitted when people ingest the parasite's eggs. Another difference is where in a person's body the adult worms typically live. Adult filarial worms typically live in tissues and organs of the lymphatic system (such as the lymph nodes) or under the skin or in the eyes, whereas worms that are not filarial typically live in the intestine.
There are many species of filarial worms, but only a few infect people. Species that infect people include
Loa loa (African eye worm), which causes loiasis
Onchocerca volvulus, which causes river blindness (onchocerciasis)
Wuchereria bancrofti, Brugia malayi, and Brugia timori, which cause lymphatic filariasis
Dirofilaria immitis, which causes dirofilariasis (dog heartworm infection)
These infections are not spread directly from person to person.
(See also Overview of Parasitic Infections.)
Symptoms of Filarial Worm Infections
Inside the body, adult filarial worms can migrate and form lumps in the lymph vessels or under the skin, depending on type of filarial worm causing infection. Adult female worms produce immature forms of the worm called microfilariae. Much of the damage and many symptoms caused by filarial infections result from the body's inflammatory responses to the adult worms or microfilariae.
