One of the most commonly discussed dangers to pets is heartworm—a disease caused by parasitic worms that affect the heart, lungs and blood vessels of animals. Unlike worms that live in the gastrointestinal tract, heartworms find their way to your cat’s heart, blood vessels and lungs, where they can grow to around a foot long and cause damage. 

If you own a cat, it’s important to understand the risks that heartworm disease pose to cats and how you can help protect your furry friend from experiencing it.

What is heartworm disease?

Heartworm disease is a condition caused by the contraction and infestation of parasitic worms called heartworms. Although heartworm is generally discussed more for dogs, the disease can also affect cats, and to a different degree than dogs. The disease is extremely serious and can be fatal. Heartworms are known to lead to heart failure, lung disease and associated organ damage over time. Unfortunately, detecting the disease early is difficult because there are very few early symptoms. A routine test by a vet is usually required for early detection.

The further the disease progresses, the worse it becomes, causing severe symptoms and sometimes death of the animal.

Heartworms can be transmitted by carrier animals and bugs. Dogs, cats, foxes, coyotes and wolves are all known carriers of the parasites. When adult worms reproduce, they create larvae that are often picked up by mosquitos.

Then, mosquitos are able to transmit the growing heartworms to new animals through their bites, depositing the parasites to new hosts. There, they make their way to the heart and grow over the course of around six months, living there for multiple years.

Because heartworm is often transmitted via mosquitos, some people believe that cats that stay indoors have a reduced chance of contracting the disease than outdoor cats. However, indoor-only cats are still at risk and should receive preventative care as much as outdoor cats.

Some areas have a much higher risk of heartworm than others. Unfortunately, heartworm continues to spread further and further each year.

Heartworm and cats

Heartworm disease looks a little different in cats than it does in dogs. Ultimately, cats are less likely to host adult heartworms, so most heartworms do not even make it to adulthood in cats. Most cats with heartworm have fewer than six adult heartworms at a time.

Heartworms are also not as capable of living in cats for as long as they can in dogs. Whereas an adult heartworm can live up to seven years in a dog, it can only live for two or three years in a cat.

However, this does not mean that the disease is any less dangerous. Heartworms do not need to be adults to cause problems. Heartworm disease can still cause significant damage to your cat’s health, and your cat’s role as a host can still perpetuate the spread of the disease to other animals.

Heartworm disease can lead to a number of problems for your cat. Most commonly, it can cause respiratory damage as the heartworms affect healthy tissue in the lungs, die in the lungs and/or cause lung inflammation. This often leads to symptoms such as coughing, wheezing, vomiting and labored breathing. Respiratory distress caused by heartworm disease is often called heartworm-associated respiratory disease (HARD).

Cats with heartworm may also lose weight rapidly, experience diarrhea and become lethargic. If the disease progresses even further, heartworms can also cause damage to the eyes and brain.

The decreased presence of adult heartworms in cats can actually make the condition harder to diagnose. In some cases, the first sign cat owners see in response to heartworm is their cat collapsing due to organ failure. For these reasons, heartworm should be taken very seriously by all pet owners.

Prevention and care

Unlike in dogs, there is no reliable treatment method for heartworm disease in cats. This means that prevention is critical for your cat’s safety and lifelong health. Most cats can receive heartworm prevention medication in the form of oral pills or spot-on topical treatments.

Unfortunately, if your cat does succumb to heartworm disease, is can be quite difficult to diagnose. Many tests for heartworm look for adult heartworms, which are not as prevalent in cats. This can cause a false-negative result. Multiple types of tests and screenings may be required to confirm a heartworm diagnosis.

Once diagnosed, heartworm in cats will require a lifelong management plan because there is no approved medical treatment. Often, this will include routine monitoring to assess the damage to your cat’s lungs and heart. Some medications may help alleviate the symptoms of the disease to make your cat more comfortable.

Although some cats’ immune systems will be strong enough to fight off the infection, you do not want to take that risk. Because of the great danger heartworm disease poses to your cat, your main concern should be with prevention to give your cat a long, healthy life.