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Heartworm Disease In Cats

Updated on October 8, 2015
Bob Bamberg profile image

Bob has been in the pet supply business and writing about pets, livestock and wildlife in a career that spans three decades.


This Parasite Doesn't Thrive Very Well In Cats

Most dog owners are familiar with canine heartworm disease because they have their dogs tested and placed on the monthly preventive medicine. Just about any animal, humans included, can get heartworms, but don't let the name fool you. Heartworms invade the lungs and other vital organs, as well.

Feline heartworm infection occurs when a mosquito infected with heartworm larvae draws blood from a cat, affording the heartworm larvae entrance into the cat’s body. They then embark upon a metamorphic odyssey that involves several molts and quite a bit of time before they end up in the blood vessels of the lungs.

It takes about 8 months for the females to mature and reproduce, which is about one month longer than it takes in dogs. Their offspring, known as microfilariae (pronounced micro-fill-ahry-uh) start the cycle anew when a mosquito takes a blood meal, including the microfilariae, from the infected cat and bites another cat to obtain a blood meal.

Before maturing, heartworm larvae can do significant inflammatory damage and injury to a cat’s lungs. In fact, this initial phase is part of a relatively new syndrome, called Heartworm Associated Respiratory Disease (HARD), and is often misdiagnosed as asthma or bronchitis.

If there’s a silver lining to this cloud, here it is: cats appear to be inhospitable hosts to heartworms, and the presence of their microfilariae is uncommon. Indeed, some cats seem to be able to rid themselves of the disease without medical intervention.

When worms are present, they are fewer and smaller than those found in dogs, their lifespan is about half of what it is in dogs, and where 40% to 90% of the worms reach maturity in dogs, up to 25% do so in cats.


The symptoms of heartworm infection in cats are inconsistent and, as is the case with so many health issues in animals, often are similar to any number of other medical problems.

In the early stages, symptoms are similar to those of asthma and bronchitis, and the disease is often misdiagnosed as one of those. Cats may or may not vomit, cough, have difficulty breathing, lose their appetite and show some weight loss.

In advanced cases, you might see blindness, rapid heart rate, difficulty breathing, diarrhea and vomiting, convulsions, and collapse. If a cat seems healthy one day and is dead the next, heartworms are usually blamed because sudden death is one of the symptoms.

The disease in cats is difficult to diagnose, but many cases are picked up by x-ray and ultrasound exams. Some tests are unreliable. Antigen tests, for instance, only detect adult female and dying male worms. Sub-adult female and male only infestations are hardly ever picked up.

Treatment pretty much consists of supportive therapy since there are currently no products in the U.S. approved for the treatment of feline heartworm infection. If an ultrasound reveals worms in certain areas of the heart, they can be removed surgically.

Feline heartworm disease: difficult to diagnose, difficult to treat, but fortunately, not as common as canine heartworm disease.



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    • Bob Bamberg profile image

      Bob Bamberg 5 years ago from Southeastern Massachusetts

      Hi Lizzy,

      Oh, they do get it, but statistically not as frequently as dogs and usually not as bad as dogs. I referenced cats as inhospitable hosts...the parasites just don't seem to do as well inside cats, and some cats are able to rid themselves of the worms without getting any treatment. They don't yet know how cats do this.

      There are tests but they're not too reliable and treatment usually means treating the symptoms. There are some preventive products on the market but they're reported to be essentially ineffective.

      There's a lot of info available from credible sources such as USDA APHIS (Animal and Plant Health Inspection Service), the AVMA, and there's even an American Heartworm Society.

      Thanks for stopping by and commenting. Nice to have you aboard.



    • DzyMsLizzy profile image

      Liz Elias 5 years ago from Oakley, CA

      Hmm...interesting, and rather scary. My vet stated that cats do not get this parasite, and so don't need testing or preventative treatment. Something about their blood being different, and essentially killing off the larvae, or some other stage of the pest so that they do not, in fact, end up with the infestation.