heartworm disease in catsSpringtime is near, and in our neck of the woods, the steamy days and nights of summer aren’t far behind. This means swarms of mosquitoes will be arriving, too. Although mosquitos may be annoying to you, they may pose a deadly threat to your cat.

Heartworm disease has long been known to affect dogs, and owners should bring their dog in annually to have a heartworm test. However, did you know that we’re finding more and more cases of heartworm disease in cats?

How Do Cats Get Heartworm?

The heartworm life cycle is complicated and lengthy, but here it is in a nutshell:

  • Heartworm microfilariae (baby worms) are picked up from an infected animal (dogs, cats, wolves, coyotes, foxes, etc.) by a mosquito bite.
  • The microfilariae develop over the course of 10-30 days inside the mosquito’s body and are transmitted to a new animal when the mosquito bites them.
  • Next, the microfilariae travel through the host’s bloodstream for several months. When they reach the heart and lungs, they mature into adults, becoming foot-long worms capable of reproduction.
  • After about eight months of infection, adult worms release microfilariae into the host’s bloodstream for about one month. The host is now a carrier for the disease and can infect other pets via mosquito bites.

Any pet exposed to mosquitos is at risk for heartworm, even strictly indoor pets (we’ve all heard that annoying buzz in our ear at night!).

Signs and Diagnosis of Heartworm Disease in Cats

Cats are resistant hosts, which means microfilariae and worms don’t live as long in a cat’s body as they do in dogs and other animals. For this reason, detecting the presence of the microfilariae and worms is more difficult in cats than in dogs.

Signs of heartworm disease in cats may be very subtle or may be extreme. Either way, diagnostic testing is needed in addition to observation of clinical signs. Symptoms may include:

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

Unfortunately, one common sign of heartworm disease in cats is sudden death. When the worms migrate through the pulmonary arteries, they can create a blockage that restricts oxygen flow to the heart. Another cause of death in cats is thought to be a reaction of the cat’s lungs to the dead or dying worms.

Diagnosis may involve blood testing, x-rays of the heart and lungs, and cardiac ultrasound or echocardiogram. Because the microfilariae live such a short time in the cat’s blood stream, repeat testing over several months may be needed.


Sadly, there is no approved drug for the treatment of heartworm disease in cats. However, there are two (not very good) options:

  1. We can use the dog-approved drug for ridding the body of heartworms. Unfortunately, as the medication kills the worms, the same reaction of the lungs may occur, causing a cat to die suddenly.
  2. We can treat a cat’s symptoms and hope they outlive the worms, which usually live 2-3 years. During this time, we treat any respiratory illness with corticosteroids and remain on the watch for any respiratory emergency that might result in the need for medication or hospitalization.

Prevention of Heartworm in Cats

Prevention really is the best option to protect your cat from heartworm disease. The Pet Experts at Springbrook Animal Care Center can recommend a heartworm preventive that’s safe, effective, and easy. Some are topical, some are chews, and others are injectable. Most have the added benefit of protecting your cat against other internal parasites as well. Lastly, don’t use your dog’s medication on your cat. They’re different, and cats need to be tested before administering any form of heartworm medication.

We hope this has been helpful. Please give us a call with any questions or to schedule your cat’s preventive care exam and heartworm test.