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Do Cats get Heartworms?

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. An incidence of 2% to 14% of all cats has been reported for endemic areas, making heartworm a concern for any cat living where there are mosquitoes.

  • The cat is not a natural host for the heartworm, which means the migrating larval heartworm is not likely to complete its life cycle. Most of the larvae that actually make it to the pulmonary artery die soon afterwards due to the massive immune attack from the feline body. Very few larval heartworms survive to adulthood in cats.  

  • 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

The cat's immune system is extremely reactive against heartworms. For this reason, it is virtually impossible to detect microfilariae in an infected cat. 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

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.

Prevention

The good news is that feline heartworm infection is 100% preventable and there are currently products on the market that are reliably effective.

The dose of ivermectin (active ingredient of Heartgard) needed to prevent heartworm infection in cats is about 4 times higher than that in dogs. Heartgard was the first FDA-approved heartworm prevention medication available for cats. It is a monthly flavored chewable available by prescription. The American Heartworm Society recommends testing prior to administration.

Advantage Multi® is a product from Bayer which combines imidacloprid for flea control and moxidectin for heartworm preventive in one product.