Do Indoor Cats Need Heartworm Prevention?

Heartworms are spread by mosquitoes, which are primarily considered outdoor pests. But if you’ve assumed that your indoor cat isn’t at risk for heartworms and heartworm disease, it’s important to understand what risks your cat is still exposed to even if they are only indoors.

Here’s why your couch-surfing kitties needs the protection of a heartworm preventive, regardless of whether they spend time outdoors.

How Do Cats Get Heartworm Disease?

Just like dogs, cats get heartworms from infected mosquitoes. When a mosquito that has been incubating heartworm larvae bites your cat, the tiny immature worms enter the bite wound and eventually make their way into the cat’s bloodstream. Here, the worms may live for weeks, months, or even years, wreaking havoc on a cat’s blood vessels and respiratory system.

Heartworm disease manifests differently in cats than it does in dogs. Dogs typically develop heartworm disease when large numbers of adult worms grow within their heart and blood vessels, while cats typically develop lung disease with chronic coughing and other breathing issues.

Keep in mind that even though most heartworms in cats die before they reach full maturity, heartworm disease is still a serious health condition in cats. Unlike dogs, cats can develop disease from both immature and adult heartworms, and a single adult worm can cause severe illness or even sudden death.

How Do Indoor Cats Get Heartworm Disease?

Indoor cats are at risk for heartworms for a simple reason: Mosquitoes can easily find their way indoors. In fact, a study conducted at North Carolina State University found that roughly one in four heartworm infections in cats occurred in indoor-only cats.

Mosquitoes can enter your home through various entry points, including air vents, garages, carports, and open doors. They’re also small enough to squeeze through tiny holes in windows, porches, and even your cat’s favorite catio screen.

It takes only one bite from an infected mosquito to give your cat a potentially fatal heartworm infection. Unlike dogs, cats have no approved treatments for heartworm infections. Therefore, heartworm prevention medication is the only way to protect them from this dangerous disease.

Another important reason to keep cats on heartworm prevention is that most heartworm preventive medications also protect against other dangerous parasites that threaten the health of cats and sometimes pose a threat to human health as well.

Depending on the product, this can include protection against common intestinal parasites like roundworms and hookworms, as well as other common parasites in cats such as fleas, ticks, and mites.

Many of these parasites are good at finding their way indoors, often hitching a ride on other pets or human clothing. If dogs also live in the house, they can easily bring in fleas picked up during their daily walks. In multi-pet households, it’s especially important to give all your pets heartworm medications that provide broad-spectrum parasite control.

It’s also important to recognize that heartworms in cats (and dogs) aren’t just a seasonal threat. The American Heartworm Society recommends year-round heartworm prevention for both dogs and cats (and ferrets, if you have them).

Mosquitoes can migrate indoors to avoid colder temperatures, and parasites like fleas can thrive year-round in warm, indoor environments. Finding a preventive medication or product that protects against all parasites is essential for your pet’s health.

How Do Veterinarians Diagnose Heartworm Disease in Cats?

While simple in-office blood tests can be used to screen dogs for heartworms, detecting a heartworm infection in cats is more complex.

Veterinarians typically diagnose cats using a combination of pet health history, physical examination, X-rays, ultrasounds, and blood tests.

According to the American Heartworm Society, veterinarians test cats for heartworms for several important reasons:

• To screen them for heartworms before they start taking a heartworm preventive medication, since administering preventive treatment to an infected cat can lead to serious health complications.

• To diagnose a cat showing signs of heartworm infection, like coughing, wheezing, or vomiting.

• To monitor cats that have been previously diagnosed with heartworms.

• To better understand the relative risk of heartworms to cats in the area.

Feline heartworm disease is believed to be underdiagnosed, in part because cats are rarely tested for it. This means the disease is more common than many pet parents realize. Together, you and your veterinarian can determine when and if your cat should be tested.

How To Protect Your Cat Against Heartworm Disease

The American Heartworm Society recommends that cats be on heartworm prevention year-round. Heartworm medication is only effective when given as directed—which means giving the medication on schedule, without missing doses.

Depending on the product, these medications are administered on a monthly or every-other-month basis, either as a spot-on treatment applied topically or as a chewable tablet. You should consult your veterinarian to find the best heartworm preventive for you and your cat.

Always follow the dosing instructions on the product label and ensure it is administered on time, according to the recommended schedule. Heartworm medications should be started in kittens by 8 weeks of age.

Finally, remember that keeping cats indoors can provide extra protection from health hazards such as certain parasites and other potential dangers in the outdoor environment.