What Is Heartworm in Cats? Symptoms, Diagnosis & Prevention

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Heartworm in cats is a serious and potentially life-threatening condition that occurs when a kitty is bitten by a mosquito that's infected with the worm parasite Dirofilaria immitis. While outdoor cats are more at risk for infection, indoor cats are also susceptible to heartworm disease since mosquitoes can easily infiltrate the barriers of doors and homes.

Luckily, there are several medications for cat heartworm prevention. Additionally, by knowing the signs of heartworm, you can ensure your kitty stays safe from this vicious disease.

Heartworm in Cats: What Is It?

Cats become infected with the heartworm parasite if they're bitten by a mosquito carrying heartworm larvae (immature worms). Then, the larvae mature and migrate from the bloodstream to their final residence in the heart and lungs of a cat. The death of these heartworms can result in a severe inflammatory reaction, which can be fatal for cats.

It's possible for signs of heartworm in cats to develop prior to the parasite reaching maturity, due to an inflammatory response in the lungs triggered by the larvae. In most cases of heartworm disease in cats, there are often only a few adult worms present. However, since the size of a cat's heart and blood vessels are smaller than those of a dog, the damage caused by the worms is significant.

Despite its name, heartworm disease in cats does affect the heart but it primarily attacks the lungs. As such, a new term has been coined to describe heartworm in cats: heartworm associated respiratory disease (HARD), reports American Veterinarian.

Some cats are able to clear the heartworm parasite through an immune response to the worms. However, even if this occurs, signs commonly seen with the disease may still occur. For most cats who have been bitten by an infected mosquito, the heartworm larvae will mature and migrate, resulting in several overt signs.

Curious domestic cat of ginger color on a leash walking in summer forest while wearing a scarf.

What Are the Symptoms of Heartworm in Cats?

The most common symptoms of heartworm in cats mimic those of feline asthma and other chronic respiratory diseases. These signs can include intermittent coughing and increased breathing rate and effort.

Signs of heartworm disease in cats can also be vague and general in nature and include mild lethargy, intermittent vomiting, weight loss and decreased appetite.

How Is Cat Heartworm Diagnosed?

A veterinarian will diagnose heartworm in cats by considering the pet's health history, physical exam findings, radiography of the chest and general blood work. A vet will also need to perform specific blood tests to evaluate for the presence of heartworm antibodies and adult heartworm antigens or proteins.

An echocardiogram (an ultrasound image of the heart) can be performed to see if there are adult worms in the heart and associated blood vessels. According to the Cummings School of Veterinarian Medicine at Tufts University, this noninvasive form of imaging can also evaluate if your pet has any other heart problems, such as valve abnormalities, tumors, dilation or muscle thickening.

A cat may need to undergo multiple tests to confirm the diagnosis of heartworm disease.

Is There a Treatment for Heartworm?

Unfortunately, there is no real treatment for cats who are diagnosed with heartworm. If a diagnosis is made, your vet and potentially an animal cardiologist can guide you on the best course of monitoring and medications to help support your cat's health.

If minimal signs are present, monitoring for spontaneous clearance of the parasite can be done with repeat blood testing. In cases where there is evidence of the disease in the lungs, cats are monitored with chest X-rays and echocardiograms, and treated with steroid medication to help reduce inflammation caused by the worms.

Cats with significant signs may require additional, more aggressive, supportive treatments such as oxygen, medications to aid heart and lung function, IV fluids and antibiotic therapy. In some cases, if there are a large number of worms in the heart and associated blood vessels, surgical removal can be attempted.

Tips for Heartworm Prevention for Cats

The good news about heartworm in cats is that it's extremely easy to prevent. There are many safe, effective and simple-to-administer medications available that can help keep your cat safe from heartworm. These medications are relatively inexpensive and are available in a monthly oral or topical form.

It's recommended that all cats, whether they live outdoors or indoors, be on year-round heartworm medication — especially if they live in areas where the disease is most common, such as the southeastern United States, maps the American Heartworm Society, or other sub-tropical climates where mosquitoes are present around the world. Consult your veterinarian to determine which heartworm preventive medication is best for your cat.

While the best way to protect your cat from mosquitoes, parasites and other threatening elements is usually to keep them indoors, this act alone may not keep them safe from heartworms. Because of how seriously this disease can affect your kitty's health, you'll want to arm them with preventive heartworm medication and keep an eye out for any tell-tale signs. By taking a proactive approach, you can keep your feline companion safe from heartworms.

Contributor Bio

Dr. Jessica Seid

Jessica Seid is an emergency veterinarian practicing in the New England area. She is a graduate of the North Carolina State College of Veterinary Medicine and has been in the field for more than a decade. When she's not helping patients, she enjoys spending time with her husband, daughter and French bulldog.

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