Do Cats Get Heartworm?

The answer is an unequivocal yes but the feline situation is vastly different from the canine situation. While it is true that the feline infection is not as common as the canine infection, the feline infection has recently been found to be a much more widespread problem than previously believed. In the past, a common statistic was that within a given geographic area, the feline heartworm infection rate was approximately 10% of the canine infection rate. Recent research indicates this is not so; in heartworm endemic areas like here in Clermont county, the incidence of feline heartworm infection rivals or surpasses that of feline leukemia virus or feline immunodeficiency virus. An incidence of 15-20% of all cats has been reported for our area, making heartworm a concern for any cat living where there are mosquitoes.

The Parasite and its Migration

  • The cat is not a natural host for the heartworm, which means the migrating larval heartworm is not likely to complete its life cycle.
  • Whereas a moderate heartworm infection in a dog would involve 25 to 50 adult heartworms, infected cats typically have less than six adult worms. Because the feline heart and blood vessels are so small, these few worms can wreak havoc. In a dog, six worms or fewer might not be considered worth treating. In a cat, a single worm could easily represent a lethal infection.
  • Whereas worms found in the canine heart can reach lengths up to 14 inches, the average length of worms found in feline hearts is only 5 to 8 inches long.
  • While an adult heartworm can expect to live 5 years in a dog, it will only live 2 to 3 years in a cat, probably due to the cat’s strong immune reaction.

Heartworm disease in cats is caused by the inflammatory reaction generated by the worm’s presence.

In dogs, heartworm disease is mostly about the obstruction of blood flow from the physical size of the worms. 

Symptoms of Disease

Symptoms of infection in cats tend to be more immune-related than heart-failure related. Cats develop more of a lung disease, complete with respiratory distress, and chronic coughing or vomiting. Feline heartworm disease is often misdiagnosed as feline asthma. Sudden death may occur just as it may occur in infected dogs. Heartworm disease is primarily a lung disease in cats, not a heart disease.

Diagnostic Testing

No single test is reliable for heartworm testing in the cat. The American Heartworm Society currently recommends using both an antigen test and an antibody test for screening apparently healthy cats. If a cat is sick and heartworm disease is suspected, both these tests are recommended, plus chest radiographs and/or echocardiography to assess heart and lung disease.


Since the major signs of disease in cats are due to inflammation and immune stimulation, a medication such as prednisone can be used to control symptoms. In general, if the cat does not appear sick, the American Heartworm Society recommends attempting to wait out the worm’s 2 to 3 year life span and simply monitor chest radiographs every 6 months or so.


The good news is that feline heartworm infection is 100% preventable and there are currently four products on the market that are reliably effective.
Revolution® is a product that covers fleas, roundworms, hookworms, and ear mites in addition to preventing heartworm in cats. Uniquely, this product is applied topically rather than orally.

The American Heartworm Society recommends monthly preventive for ALL CATS in heartworm endemic areas like Ohio.
By Dr. Dan Meakin

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