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Heartworm in Cats — Diagnosis, Treatment and Prevention

Heartworm is rarer in cats than it is in dogs but when cats do contract it, the outlook isn’t good. Learn more about heartworm in cats and the steps you can take to prevent it in the first place.

Jackie Brown  |  May 11th 2018


Heartworm in cats is devastating. Even though cats are not natural hosts for heartworms (which are transmitted by mosquitoes), cats can and do contract the parasites, and when they do, the outlook is grim.

First, what is heartworm in cats?

A cat sick or sleeping while being pet by a human.

What is heartworm in cats and can you prevent it? Photography @Gumpanat l Getty Images.

“Heartworm disease in cats is most often associated with asthma-type symptoms and sudden death,” says Andrea Sanchez, DVM, Senior Manager of Veterinary Policies and Standards for Banfield Pet Hospital. “It’s important to know that many pets infected with heartworm show no signs of the disease but can act as a source of infection for other pets.”

One tragic example of heartworm in cats

Heartworm disease in cats is much rarer than it is in dogs, but it’s more devastating. There is no treatment and it’s often lethal. “One of the most tragic cases early in my medical career was a cat that was nearly three years old and died suddenly,” says Ernie Ward, DVM, CVFT. “The owner was convinced that he had been poisoned.”

Dr. Ward suggested that the owner do a necropsy (the term for the procedure known as autopsy in humans), and what they found was not evidence of poison, but a single heartworm, which was the cause of death.

“This cat was indoors, in the prime of his life and yet he was felled by a single heartworm,” Dr. Ward explains. “Cats are not the host for heartworms, they are an accidental infectee. That’s why we don’t see the hundreds of heartworms that might live in a dog’s heart. The cat’s immune system kills most of them, but if one or two adult heartworms survive, they cause a form of anaphylaxis, a strong immune response reaction that kills the cat.”

How are heartworms in cats diagnosed?

Heartworms are diagnosed with a simple blood test. If your cat is diagnosed with heartworms, she will need to be closely monitored by your veterinarian. Supportive treatment can help prolong your cat’s life. According to the American Heartworm Society, some infected cats might even experience spontaneous clearing of their heartworm infection, although permanent damage to the respiratory system may have occurred.

What cats are at risk for heartworms?

Anywhere you find mosquitoes, you will find heartworm. “At one time, heartworm disease was thought to pose a threat only to pets in the southeastern U.S.,” Dr. Sanchez says. “Unfortunately, this is no longer true. Heartworm infection has been found in all 50 states and Puerto Rico. Your vet may be especially concerned in the weeks and months following tropical storms and hurricanes.”

How do you prevent heartworm disease in cats?

Preventing heartworm disease is easy with a monthly heartworm preventive (chewable or spot-on topical), but many cats go unprotected. Just because your cat lives indoors doesn’t mean she’s immune to heartworm. All it takes is a bite from a single mosquito. “Dogs and cats, regardless of their age, gender or habitat — including indoor and outdoor — are susceptible to heartworm infection,” Dr. Sanchez says. “Just like you, your pet can get a mosquito bite inside the home.”

Some cat owners might balk at the expense of monthly heartworm prevention, but the fact is, heartworm preventives are more affordable than ever before. “It’s much cheaper than it was 30 years ago,” Dr. Ward says. “The patents have expired and there are many generic forms. We also know that these are incredibly safe drugs. There are some people who think, ‘It’s not going to happen to me, it won’t happen to my pet.’ The reality is it only takes one mosquito bite.”

Tell us: Has your cat ever experienced heartworms?

Thumbnail: Photography by Nikolay Bassov | Shutterstock. 

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