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Heartworm in Cats: What You Need To Know

Est. read time: 4 min.

April is National Heartworm Awareness Month. If you have a dog, you’ve likely heard of heartworm disease before. Your veterinarian may have even shown you a plastic model of a dog heart filled with these spaghetti-like white worms at your last veterinary visit. Veterinarians are always recommending heartworm preventative in dogs. (My dog is on preventative medication year-round in Minnesota!) Why? Because heartworm disease is potentially fatal in pets. What most pet parents don’t realize is that heartworm disease arises in more than just dogs. Today we’ll cover what you need to know about heartworm in cats.

So, what exactly is heartworm disease?

Heartworm disease is caused by a foot-long Dirofilaria immitis worm that lives in the blood vessels, lungs, and heart of certain animals. Dogs are actually one of many species that act as natural hosts for this worm; in other words, it means that the heartworms can live in your dog, grow into big adult worms, mate with other worms, and produce more offspring—all while circulating in your dog’s blood. Then, when a mosquito bites a heartworm-positive dog, the mosquito can transmit it to the next susceptible dog!

Unfortunately, these baby larvae (microfilaria) and adult worms can result in severe damage to your dog. I’ve seen dogs with dozens to hundreds of heartworms clogged in their lungs and heart. In dogs, heartworm disease can cause severe heart failure, including fluid accumulation in the abdomen, difficulty breathing, chronic lung disease, pulmonary embolism (clots to the lungs), and organ damage long-term. Treatment is available, but is very expensive (> $1,000) and risky. That’s why long-term preventative medication (a once-a-month flavored pill or 6-month long-acting injection) is the safest, least expensive thing for your dog.

Not only does heartworm affect dogs, but it also affects:

  • Wolves
  • Foxes
  • Sea lions
  • Coyotes
  • Humans (rarely)

But do cats get heartworm?

While heartworm in cats is less common, cats can get heartworm disease—and there’s no good treatment (unlike dogs).

The difference in heartworm in cats—as compared to dogs—is that cats aren’t good hosts for this disease. In other words, the adult heartworms often die in the cat before they can spread to another animal (as compared to dogs, wolves, and coyotes that act as hosts to other animals!). That said, in cats, the worms can cause severe damage before they die–including a disease called “heartworm-associated respiratory disease.” Just 1-2 heartworms can be fatal to a cat.

And when it comes to treating heartworm in cats? Well, there is no treatment for cats—the medication (melarsomine, known by the more common trade names “Immiticide” or “Diroban”) for treating dogs can’t be used in cats… meaning the only way to protect your cat is with prevention (also a once-a-month, flavored pill that your cat will view as a treat!).

What are signs of heartworm disease in cats?

Clinical signs of heartworm in cats include:

  • Coughing (similar to feline asthma)
  • Periodic vomiting
  • Not eating
  • Drooling or acting nauseated
  • Wheezing
  • Weight loss
  • Collapse
  • Seizures
  • Ascites (fluid in the abdomen)
  • Acute death

Which cats are at risk?

Unfortunately, outdoor cats are more at risk, as they are more exposed to mosquitoes. Also, cats living in the south, southeast, midwest, and northeast United States. That said, heartworm disease has been reported in all 50 states—so it’s out there!

How do I keep my cat safe?

The best way to keep your cat safe is by keeping them indoors and using heartworm preventative for cats. However, please know that mosquitos are adept at coming inside, and I’ve even found them in my house in the middle of Minnesotan winters! Heartworm medications like Advantage Multi, Heartgard, and Revolution (listed in alphabetical order) can be safely used year-round in cats to help protect your cat.

For more great information specifically regarding heartworm in cats, check out the American Heartworm Society.

heartworm in cats


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