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Dog Heartworm Infection


By Richard D. Pearson, MD

Dog heartworm infection is caused by the roundworm Dirofilaria immitis, which is transmitted to people by infected mosquitoes.

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. The 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.


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


  • Removal and examination of a sample of lung tissue

Doctors may discover the infection when they see a lump in the lungs on a routine chest x-ray. The lump resembles a lung tumor.

To confirm the diagnosis, doctors remove and examine a sample of lung tissue.


  • Resolution of infection on its own

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

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