heartworm in catsA lot of time and education goes into discussing heartworm in dogs. As a result, most dog parents are aware of this parasitic disease and take steps to prevent it in our canine companions. But most cat parents aren’t aware that cats can get heartworm, too.

Because mosquito season is on its way, your friends at Clairmont Animal Hospital decided that it was high time to give you a peek into this disease in our feline friends.

How Is Heartworm Disease Transmitted?

The heartworm life cycle is complex and takes several months to complete.

  • A mosquito bites an infected animal (cat, dog, or wild species), taking up the baby heartworms, or microfilariae, from the infected animal’s blood.
  • The microfilariae develop in the mosquito’s body for 10-30 days.
  • The mosquito then bites a cat, transmitting the microfilariae into the cat’s bloodstream.
  • The microfilariae further develop in the cat’s body, eventually finding their way to the heart and pulmonary arteries, where they mature into foot-long, adult worms, capable of reproduction.
  • After about 7 months after infection, the adult heartworms release new microfilariae into the cat’s bloodstream.

Signs of Heartworm in Cats

Clinical signs may be quite unspecific, a challenge in diagnosing cats. They usually look like symptoms of other diseases as well. Signs may include:

  • Sudden onset of coughing
  • Wheezing
  • Weight loss
  • Vomiting
  • Rapid breathing

On occasion, an apparently normal cat will be found dead, and examination reveals heartworm disease. Sudden death is thought to be caused by a reaction of the cat’s immune system to the dead or dying worms, or a reaction to the dead or dying worms entering the pulmonary arteries and blocking oxygen flow.

Heartworm Differences Between Cats and Dogs

Although they are transmitted the same way, there are some differences between heartworm disease  in cats and dogs. Sadly, these differences often translate into a disadvantage for your cat. Here are the main differences:

  • Unlike dogs, cats are resistant hosts for heartworms. They usually have only 1-6 heartworms that survive to adulthood, compared to upwards of 30 in dogs.
  • Even a few worms can cause serious illness in cats, most notably heartworm associated respiratory disease, or HARD.
  • Diagnosis of heartworm in cats can be elusive, requiring blood tests, x-rays, and cardiac ultrasound or echocardiogram. Because of the length of the heartworm life cycle, tests may have to be repeated over the course of months in order to get a definitive diagnosis.
  • There is currently no approved drug to clear heartworm infection in cats. The only treatment option is to treat the clinical signs in the cat, and hope that the cat outlives the worms. Heartworms typically live only 2-3 years in the cat, as opposed to 5-7 in the dog, and a respiratory emergency and sudden death may occur at any point during that time.


Because there is no good treatment option for heartworm in cats, prevention is absolutely the best option for cats. Luckily, prevention is as easy in cats as it is in dogs. We can talk to you about a cat-approved heartworm preventive, which can be given monthly as a chew or topical, or every 6 months as an injection.

It should be noted that keeping your cat indoors does not prevent them from getting heartworm. More than 30 species of mosquito have been shown to carry the disease, and it only takes one mosquito getting indoors to put your cat at risk.

The bottom line: Don’t take chances with your cat’s health. Talk to us about starting a heartworm preventive for your cat. If you have any questions about this or your cat’s health in general, give us a call.

But most cat parents aren’t aware that cats can get heartworm, too.