Heartworms and Cats

New Study Reveals Disease Is Not Just For Dogs

Cat is examined by a veterinarian

A new landmark study by researchers at Auburn University revealed that cats are also in danger, and that heartworms do not need to reach maturity to impact their health. This feline condition is coming to be known as HARD, or Heartworm Associated Respiratory Disease, and can be particularly devastating.

Understanding How Heartworms Attack

Heartworm disease is caused by different stages of the parasitic worms living and dying throughout the animal’s body—mainly in the blood vessels, heart, and lungs. They are transmitted in the larva form through bites from infected mosquitoes. 

If the animal is not taking preventive medicine, the larvae mature into adult worms and the results are potentially fatal.

Cats Are Susceptible, Too

Cats are not the preferred target of most mosquitoes or the preferred host for the heartworms. They appear to have a natural resistance to infection and can live with very low worm burdens without ever showing any related clinical signs. Cats tend to have fewer worms than dogs, and the worms are more short-lived (two to three years), as compared to dogs (five to seven years).

Because of this lower rate of infection and lower worm burden, heartworm disease is more difficult to detect in cats. This has led it to mainly be thought of as a dog affliction.

However, new studies are showing that heartworm disease in cats is much more common than many in the veterinary community previously thought.

Dr. Tom Nelson, a former president of the American Heartworm Society, discovered that in a random sample of cats, the incidence of heartworm infection was actually higher than rates of the more well-known conditions of feline leukemia and feline AIDS.

Symptoms to Be Aware Of

You may not be aware for some time that your dog or cat has been infected. It can take months, or even years, for the heartworms to accumulate, sometimes after many bites from infected mosquitoes. This is why yearly testing is highly recommended.


Heartworm disease in cats can cause nonspecific signs seen in many other diseases, including vomiting, diarrhea, lethargy, and weight loss.

Dogs in the early stages may show no symptoms. However, once the worms mature and multiply, your dog may have a persistent cough. He may not want to run around, and a game of fetch may become too taxing for him. He may have a decreased appetite, and he may lose weight.

Heartworm disease in cats can cause nonspecific signs seen in many other diseases, including vomiting, diarrhea, lethargy, and weight loss. More specific signs can be very sudden in onset, and include coughing and difficulty breathing. Because of this sudden onset, HARD is often misdiagnosed as asthma or heart disease.

Take Preventive Measures

Kittens play

If you think your pet has been exposed to mosquitoes or has any of the signs suggestive of heartworm disease, bring him to your veterinarian. As heartworm disease is often difficult to detect in the early stages (the first 7 months), various forms of blood tests may be needed to evaluate your pet’s health.  More advanced tests may include chest X-rays and a heart ultrasound. 

Heartworm disease has been found in animals in all 50 states. However, certain parts of the country have a higher incidence, particularly the mid-Atlantic states and the Southeast.  Owners living in or traveling to these areas should be especially diligent about preventative measures. Although heartworm prevention has always been considered in dogs, it should also be considered in cats that are at risk.

Keeping Your Pet Safe

The good news is heartworm disease can be thwarted with proper preventive measures, making it simple to protect your pet.

Keep in mind that while outdoor cats are more susceptible, indoor cats can also become infected. Even if the cat clears the infection, the immature or adult worms that die can cause an inflammatory reaction that can cause significant respiratory disease. Once heartworms mature in cats, there is no definitive cure, making preventive measures vital.

Talk to your veterinarian about what method is best for your pet. There are daily and monthly tablets, as well as chewables and topical treatments that stop the development of heartworms before they can reach the lungs and possibly the heart. Once infected with heartworms, treatment options are available for dogs, but are much more complicated in cats. Often symptomatic and supportive care is all that can be done for cats, while giving them a chance to clear the infection on their own. 

More than 114,000 VPI policyholders enrolled in routine care coverage filed claims for heartworm prevention, with nearly 88,000 claims filed for testing. Preventive products include Heartgard, Advantage, Revolution, Triheart, Proheart and Sentinel and, when used correctly, can keep your pet heartworm-free.  Discuss which preventative medication is best for your dog or cat with your veterinarian. 

There are many things that can impact your pet’s health. Heartworm disease does not have to be one of them.


If you'd like to read more about preventative measures, you may enjoy learning more about toxic flea and tick medications.


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