Heartworm disease in cats

Apr 12, 2022

Many cat owners wonder if cats can get heartworm; we usually hear about heartworm affecting dogs. Cats can definitely get heartworm but the disease affects cats differently than dogs. That’s because heartworms are less likely to achieve adulthood in cats; unlike dogs, cats’ immune systems have the ability to kill most heartworm larvae before they grow into adults. However, if your cat is bitten by a mosquito that is carrying heartworm larvae, she is still at risk of developing heartworm disease or becoming ill from her body’s overreaction to them.

You may view mosquitoes as a summer nuisance, swatting them away when you hike, and casually lighting a citronella candle on the patio at dusk. But beware: blood-thirsty mosquitoes actually pose a serious threat to the health of your cat, and can lead to the death of your beloved feline.

How do cats get heartworm?

Cats can get heartworm by being bitten by a mosquito that is carrying the heartworm larvae. Heartworms can grow up to a foot long, and can take up residence in your cat’s heart and lungs. Dogs are more prone than cats to adult heartworm infestation, but cats are not safe. While dogs infected with heartworm may have dozens or even hundreds of these squirming parasites inside their bodies, it only takes a few — or even one — to make your cat very ill, and shorten your cat’s life. Cats can even become ill from their body’s reaction to the larvae themselves.

Mosquitoes transmit heartworm larvae in a single bite

Mosquitoes feed by landing on the skin of any warm-blooded animal and sucking their blood. When a mosquito sucks the blood of a host animal that is infested with adult heartworms, the insect also picks up what are called microfilaria, or baby heartworms. And when the mosquito flies off and feasts on its next host, it injects these larvae into the skin of the new animal, allowing heartworms to develop inside the host’s body. The babies mature into adult worms in about 6 months, and can live for up to 2 or 3 years in your cat. Each mosquito season can introduce new microfilariae into your pet, via mosquito bites.

How is heartworm in cats diagnosed?

Diagnosis can be difficult and requires a physical exam, X-rays, blood tests and sometimes an ultrasound. Feline heartworm disease has no approved drug treatment, so prevention is key. The medications currently used to successfully treat cases of heartworm in dogs cannot safely be used on cats. Therefore vigilant protection is your best line of defense.

How to protect your cat from heartworm

As mentioned, there are no approved heartworm treatments for cats to treat an infestation once it happens. However, there are medications that you can give to your cat to prevent heartworms. Preventatives include moxidectin or selamectin topical solution, and ivermectin or milbemycin oral tablets. Some of the brand names of these medications are Revolution, Advantage Multi, and Heartgard. You’ll need a prescription from your veterinarian to obtain preventative heartworm medication. These medications kill the microfilariae that were injected into the cat via mosquito in the last 30 days; therefore they are given every month, year-round.

Does a cat’s fur coat protect her from mosquitos?

The short answer is no. You might think that your cat’s fur is sufficient protection from hungry mosquitoes, but it’s not. Mosquitoes often target the exposed skin of the ears and nose, and can also probe into the more densely furry areas of your cat’s body to get their next gory fix.

Are indoor cats at risk of heartworm?

Keeping your cat indoors is prudent for many reasons, but it is not a guarantee of safety from mosquitoes. Since mosquitoes often get past screens on doors and windows and invade our living spaces, your indoor cat is not guaranteed to be safe from heartworm-carrying mosquitoes. Indoor cats need to be given monthly heartworm prevention year-round.

Mosquito-proof your property

Mosquitoes breed in standing water. You don’t need to live near a pond, swamp or bayou to foster a breeding ground for them. Mosquitoes only need a few inches of standing water to breed; and they can get the job done in a kiddie pool, bucket or watering can, birdbath, or even the saucer under a flowerpot. Just a spatter of rain or a puddle around a leaky sprinkler head can make a perfectly suitable mosquito nursery, so monitor your garden closely for standing water. Doing so will reduce, but not eliminate, the chance your cat will be bitten by a heartworm-infected mosquito.

talk to an airvet veterinarian for medical care for your pet

Symptoms of heartworms in cats

The symptoms of heartworm in cats can vary wildly from none to mild to very severe:

  • Coughing, wheezing, difficulty breathing
  • Asthma-like attacks
  • Periodic vomiting
  • Loss of appetite
  • Weight loss
  • Difficulty walking
  • Fainting and collapsing
  • Seizure
  • Swollen, tender abdomen
  • Often, no signs are noticeable until the sudden death of the cat

When a heartworm dies inside your cat, severe complications including blood clots and lung inflammation may follow. Unfortunately, many cats die when the heartworm(s) they are carrying die.

Heartworm associated respiratory disease (HARD)

Even though cats have less chance than dogs to harbor adult worms in their hearts, the immature worms can still cause a great deal of damage. The larvae and microfilariae trigger an immune reaction in cats, which most affects their respiratory system – a condition known as “Heartworm Associated Respiratory Disease” or “HARD.” This means that cats often show respiratory, rather than cardiovascular, symptoms as one might expect.

How to treat heartworm disease in cats

There is no treatment for heartworm disease in cats once your cat is infected. Therefore it’s vitally important to use heartworm prevention – to avoid heartworm disease altogether. If your cat is diagnosed with heartworms, your veterinarian might recommend that you begin prevention anyway. The medication won’t affect the adult worm(s), but prevent further damage to your cat from new microfilariae from mosquitoes.  If the heartworm disease worsens and your cat is showing severe symptoms, your cat may be hospitalized to provide supportive care, like intravenous fluids and medications. In extremely rare cases, surgery has been performed by cardiologists to physically remove heartworms via a catheter placed into the heart. This is very difficult and is dangerous for the cat. Prevention is the key.

Discuss heartworm prevention with a vet

Mosquitoes are everywhere and The American Heartworm Society reports that heartworm is detected in all 50 states and all year round – even winter, since the lifecycle of the parasite is so long. The Society recommends that all cats in the US be given prevention monthly, which requires a veterinarian’s prescription. Talk to a member of Airvet’s professional team of veterinarians about feline heartworm prevention.

Stay vigilant and recognize that if a mosquito (or flea, or tick) can find you, the hungry pest can also find your cat.