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How Common is Heartworm in Cats? Our Vet Explains

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	Dr. Lauren Demos (DVM) Photo

Written by

Dr. Lauren Demos (DVM)


The information is current and up-to-date in accordance with the latest veterinarian research.

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Heartworm is a disease that we generally think of in dogs. And our experience with heartwork in this species is often all about routine testing, prevention, and rarely, serious illness. However, much less is discussed about heartworm in cats. In fact, most people don’t know that cats can even get heartworm!

Thankfully, heartworm in cats is a little different than in dogs. For one, heartworm disease is much less commonly seen in cats than in dogs. This doesn’t mean that cats don’t get heartworm—they just don’t as often develop the severe sickness that can come with high numbers of heartworm infections.

However, in the rare instances a cat does become sick with heartworm disease, it can be fatal, just as it can be in dogs. As our means of testing for heartworms improve over coming years, and as heartworm disease spreads to more parts of the world, it is likely we will see higher numbers of cats with heartworms, as a result. With that in mind, here is more information about this disease in cats.

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How Common is Heartworm in Cats?

Feline heartworm disease is often underrecognized in cats, especially when compared to it being a well-known cause of illness in canine counterparts. Heartworms are a type of parasite that can infect any cat, regardless of age, breed, or whether they live indoors or outdoors.

It’s difficult to say just how common heartworm is in cats, because testing for heartworms in this species is quite difficult. Why? Because cats tend to be infected with smaller numbers of adult heartworms, and most testing only detects adult female heartworms. So, whereas dogs might have four or more heartworms when infected (sometimes many more), cats tend to only have one or two.

cat and vet
Image Credit: Stock-Asso, Shutterstock

Therefore, when testing cats for heartworm, they often test negative, even though a worm may actually be present. This has likely played a part in the traditional thought that cats don’t get infected with heartworms, and therefore, don’t need heartworm preventatives. Alternative tests that check for antibodies are available. However, they take weeks after the initial infection to produce a positive result.

Heartworm itself is a bloodborne parasite that is transmitted to cats through mosquito bites. Therefore, a cat must live in an area with infected mosquitos. Traditionally, this tended to be more southern and temperate locations, but as winters become milder throughout many geographic regions, heartworm is now also found further north.

This also previously meant that certain locations that were farther north might not have needed to treat cats at all for heartworm in the colder months. But, again, with more temperate winters in these regions, that may no longer be the case.

Are Cats Likely to Get Heartworms?

The answer is: with cats, it depends. Cats can certainly develop heartworm infections, though, in comparison to dogs, they seem a bit more resistant to infections.

Also, heartworm is almost a misnomer with cats. This is because heartworm in cats actually tends to live in the arteries in the lungs, rather than in the heart. This also means that most signs of heartworm in cats tend to be associated with the lungs—including a cough, or other changes in breathing. In worst case scenarios, heartworm can also lead to sudden death.

tabby cat lying on the floor
Image Credit: Piqsels

Additionally, heartworm infections in cats don’t always end after the initial infection. In some cats, heartworm infections can cause significant inflammatory reactions, which can damage the sensitive lung, or heart tissues. This may mean that a cat can have a chronic cough that arose from a heartworm infection years before. Once these inflammatory changes have occurred, they are generally irreversible.

Further, in recent years, it has been found that heartworm can themselves be infected with a unique type of bacteria. While the significance of this infection is not fully understood, there are suggestions that the bacteria may exacerbate heartworm-related illness in pets, which is yet another reason why heartworm disease in cats can be bad news.

Good News: Heartworm Infections Can Be Prevented

The above info may sound disheartening, but the good news is that medications can be prescribed by a veterinarian that prevent heartworm infection. Most of these medications are easy to give to a cat (many are topical, which means a liquid placed onto the cat’s skin), and are needed once a month, at most. To be effective, these medications must be used regularly, and during all parts of the year when heartworm infections can occur.

There is no cure for feline heartworm disease, and prevention is far easier than attempting to deal with heartworm once a cat is infected. If a cat is diagnosed with an active heartworm infection, a vet may recommend an ultrasound of the heart or lungs to look for heartworms, or x-rays to survey the lungs for changes relating to the infection.

Treatment is generally supportive, to help keep a cat comfortable until the infection resolves. If clinical signs occur, such as a cough, a vet may consider prescribing medications to help reduce the impact and frequency of these signs.

cat having an ultrasound in vet clinic
Image Credit: Libre, Shutterstock

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Cats can get heartworm infections—though, due to smaller numbers of worms in the course of infection, and because the disease causes more subtle clinical illness in many feline patients—it is not diagnosed as frequently as it is in dogs.

Because the disease can be prevented, ensure your cat has a close relationship with their veterinarian, and is on appropriate treatment for your local geographic region. Cats on routine preventatives are highly unlikely to get heartworm. So, why take the chance when there is an easy solution?

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