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Filarial Worm Infections Overview



Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision Sep 2020| Content last modified Sep 2020
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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

Most filarial infections occur in tropical and subtropical areas.

Infection with the dog heartworm Dog Heartworm Infection Dog heartworm infection is caused by the roundworm Dirofilaria immitis (or another similar roundworm), which is transmitted to people by infected mosquitoes. Dog heartworms cannot complete their... read more (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.


Filarial worm infections are transmitted as follows:

These infections are not spread directly from person to person.

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.

When lymphatic tissues (cells and organs that make up the lymphatic system) are involved, adult Wuchereria or Brugia worms and the inflammation that accompanies them can block lymph vessels, causing areas of the legs, arms, or genitals to become inflamed and swell. After many years, the legs, arms, and genitals may become massively enlarged and disfigured.

Circulating microfilariae of Wuchereria or Brugia can induce allergic reactions in the lungs resulting in cough, shortness of breath, and asthma-like symptoms. Adult Loa loa worms migrate under the skin causing temporary nodules and occasionally cross the eye under the clear, outer membrane (conjunctiva). Adult Onchocerca live in nodules under the skin and produce microfilariae that cause itching and damage to the skin. They also enter the eye and cause inflammation and scarring that can result in blindness after many years.

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Respiratory Syncytial Virus (RSV) Infection and Human Metapneumovirus Infection
Respiratory syncytial virus (RSV) infection and human metapneumovirus infection (hMVP) cause upper and sometimes lower respiratory tract infections. Symptoms of both viruses are similar although the viruses are different. In which of the following ages groups is RSV a very common cause of respiratory tract infections?
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