Heartworms in Cats – Causes, Treatment and Prevention

Picture of woman holding a Siamese cat

Heartworm infestations in cats are caused by the Dirofilaria immitis, a parasitic roundworm. The severity of this particular medical condition depends on the number of worms that are present inside your cat’s body, the duration of the infestation, as well as the body response of the host.

Right from the beginning, we might be able to put your mind at ease at least to some extent by telling you that heartworms in cats are a lot less common than they are in dogs. If you make sure that your cat receives preventative medication for internal parasites, the likelihood of your pet being affected by a heartworm infection is very low.

Not all cats have the same resistance when it comes to their bodies fighting off internal parasites. Besides, not all cats are exposed to heartworms in the same manner. For example, outdoor animals have an increased risk, and they are twice as likely to contract heartworm disease compared to their indoor counterparts.

In this article, we will look at some of the causes, whether there are any treatment options, as well as prevention methods for heartworms in cats.

What Are the Causes?

We’ve already established that this parasitic infestation is caused by Dirofilaria immitis, but unlike many other parasites that can be transmitted from one animal to the next or through fleas (as is the case with tapeworms, for example), this one can be spread by mosquitoes, which makes its prevention extremely challenging.

The mosquitoes carry the heartworm larvae from one infested cat to another. If your cat is bitten by such an infected vector, it will release microfilaria into the pet’s bloodstream. It takes approximately six to eight months for the microfilaria, which are basically microscopic babies of the Dirofilaria immitis, to develop into adults. Unfortunately, adults can live up to two to three years.

How Can You Tell If Your Cat Has Heartworms?

Because it takes so many months for the microfilaria to turn into adults, it can be very difficult for you to realize that your cat is a host of this parasite. There are no definitive clinical signs that could indicate the existence of heartworm disease, and its late discovery can happen when the cat’s body lacks the natural defense mechanism to tackle the infestation.

There are some health signs that could indicate the presence of heartworm disease and they range from coughing and vomiting to difficult breathing, lethargy, convulsions, blindness, or fluid in the lungs. Unfortunately, these symptoms become discernible once the disease has already become very severe. In some cases, it is diagnosed post-mortem, and yes, that means that it can be a lethal condition.

If you notice any of these signs, take your cat to the vet as soon as possible, even if the symptoms don’t pertain to heartworm disease. They could still be signs of another medical condition that needs to be diagnosed.


Not only is it difficult for the pet parent to tell what’s wrong with the cat, but it can also be the same for the medical professional. Unlike heartworms in dogs, there are no specific tests for diagnosing the condition in cats.

The vet can perform an array of medical investigations from urinary analyses to antibody tests, X-rays, and ultrasounds, and a white blood cell count can also be useful in determining whether there’s a higher number of Eosinophils, which are typically present when heartworm disease has developed.

Can Heartworm Disease Be Treated?

To this date, there is no viable heartworm medicine that can eliminate an active infestation. Therefore, if the cat is diagnosed with this medical condition, it’s impossible to cure. While the disease can’t be fought off with the help of medication, that doesn’t mean that the cat’s health state is going to get worse and worse or that the animal is going to die soon. There are healthy cats that can outlive heartworm infections and they can go on to live happily for many years after being diagnosed.

Along with the veterinarian, you can develop a plan that involves stabilizing and monitoring your cat as the animal begins to fight off the infection naturally. We mentioned that heartworms live for two to three years, so if you have a completely healthy feline companion, your pet might be able to produce a sufficient amount of antibodies to fight off the infection with time.

What is very important for you to be aware of is that, once your cat has been diagnosed, you will have to take him or her to the vet regularly. The animal might be prescribed medication that can manage the symptoms, as well as drugs to reduce inflammation. If the condition is more severe, your pet might require drugs for heart and lung issues, antibiotics, intravenous fluids, or nursing care.

If your cat is healthy and lucky enough to be able to fight off the infection on its own, you have to ensure preventative care. Susceptibility is high among cats that have been infected in the past, so you have to do your best to make sure that there is no way that your cat can be affected by heartworm disease in the future.


You’ll be happy to know that there are heartworm preventives readily available, and you can get one for your pet from the vet. Usually, you have to administer the medication every month, and it can come in the form of a chewable or spot-on topical product.

One mistake that many cat parents make is believing that, if their cats only live indoors, they can’t be exposed to such parasites. As we’ve already discussed in the intro, heartworms are carried by mosquitoes, and there is no absolute way of making sure that no mosquito ever enters your home. If you can get bitten by one, so can your cat.

Some cat parents will be more or less wary when it comes to spending money on monthly heartworm prevention, but the truth is that treating, or rather, trying to treat the medical condition is extremely difficult if not impossible, in some cases, and that’s why the expense is worth it. Even if Dirofilaria immitis infestations are considerably less common in cats than they are in dogs, that doesn’t mean that your own pet isn’t at risk. It takes just one mosquito bite.

Heartworms can be more or less common throughout the world, and if they aren’t a problem in your local area now, they might be in the future. Furthermore, if you travel with your cat to a region where the prevalence of heartworm disease is high, you are putting your pet at risk. Needless to say, most of the heartworm infections are diagnosed in areas where mosquitoes live in large numbers, such as wetlands, for example.


Although less common in cats than in dogs, heartworms can be a serious health problem. Due to the parasite’s life cycle, your cat might not manifest any symptoms until it is much too late. The parasite is transmitted through the bite of mosquitoes, and using preventive medication regularly is highly recommended because there’s no treatment for the disease.



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