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Dog Heartworm Infection

(Dirofilariasis)

By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

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 life cycle in people and do not survive for very long in people, so people are rarely affected.

  • Most infected people do not have symptoms, but if the worm travels to the lungs and dies there, people may cough and have chest pain.

  • Doctors may discover dog heartworm infection when they see a lump in the lungs on a routine chest x-ray.

  • No treatment is needed because the infection resolves on its own.

Dog heartworm infection is a filarial worm infection that rarely affects people because the worms cannot complete their life cycle in people and do not survive for very long in people.

Dog heartworm infection can be transmitted when an infected mosquito bites a person and deposits larvae of the worm in the bite. The larvae usually die in the skin. However, sometimes the larvae live long enough to travel through the blood to the lungs and die there, forming a lump (nodule), which may be seen on a chest x-ray. Rarely, larvae travel to the eyes, brain, or testes and form lumps there.

Symptoms

Larvae that die in the lungs may cause no symptoms, although some people have a cough and chest pain. Rarely, they cough up blood.

Diagnosis

  • Removal and examination of a sample of lung tissue

Doctors may discover dog heartworm infection when they see a lump in the lungs on a routine chest x-ray. The lump can resemble a lung tumor. Doctors may take a sample of the lump (biopsy) to be sure that it is not a cancer.

To confirm the diagnosis of dog heartworm infection, doctors may remove and examine a sample of lung tissue.

Treatment

  • Resolution of infection on its own

No treatment is needed for infected people. Dog heartworm infection resolves on its own.