Cat Heartworm

"While not a natural host, cat heartworm (FW) is becoming more common in cats. It is contracted from mosquito bites after the same mosquito bit an infected dog. Symptoms include vomiting and diarrhea. Treatment options are limited for this serious condition."

Heartworms in cats live in the pulmonary arteries (arteries going to the lungs) and in the the heart itself.

Getting Cat Heartworm Disease

Cats are unlikely hosts for heartworm. They get heartworm disease if bitten by an infected mosquito who transfers worm larvea into the cats tissue after biting an infected dog. The larvae hatch, turn into worms and then travel up a vein into the heart. The disease is serious since the cat has a small heart so only 1 to 2 worms can cause serious injury.

There are four factors that will affect how your cat reacts to heartworms:

- Number of worms
- Health of your cat's immune system
- Length of time your cat has the worms
- How active your cat is. Cats that are active tend to get a more severe case of heartworm disease than inactive cats.

Heartworms in cats tend to be smaller than those in dogs and have a shorter lifespan (2 to 3 years).

Symptoms of Cat Heartworm

There are few symptoms of feline heartworm. Symptoms include coughing, vomiting, weight loss, seizures, rapid or difficulty breathing (dyspnea) and sudden death. These symptoms often go unnoticed or are attributed to other causes and are not recognized as signs of heartworm.

Diagnosis of Cat Heartworm

There are several ways to diagnose feline heartworm disease.

There are two types of blood tests that can be done. One looks for antibodies, which means the cat's immune system has been exposed to heartworms. The worms may be living or dead. The other blood test looks for antigens. It detects the presence of adult female heartworms. Both tests are used together to look for heartworms.

X-rays are also used to look at the size and shape of the heart and pulmonary arteries. The arteries often come to an apparent blunt stop near the lungs where they are clogged with worms.

An ultrasound can show a better picture of the arteries, and can often even show the worms themselves.

Treatment of Cat Heartworm

Cats with heartworm are placed on a monthly preventative and short-term corticosteroid therapy (prednisone) to manage respiratory signs of heartworm disease.

The only other option is to treat the symptoms of cat heartworm disease and hope the cat outlives the heartworms. Heartworms live about two years, so several months of treatment will be required. When cats are in a crisis, they will be treated with oxygen, corticosteroids to relieve the reaction that is occurring in their pulmonary arteries and lungs, and if necessary, drugs to remove fluid from their lungs (diuretics). There will always be the threat of an acute crisis or sudden death.

Feline Heartworm Prevention

It is strongly recommended that you use heartworm prevention medication with your cat. There are three drugs with FDA approval marketed for use in cats. Ivermectin is provided in a chewable formulation (Heartgard brand), milbemycin as a flavored tablet (Interceptor brand) and selamectin (Revolution brand), a broad-spectrum parasiticide, comes in a topical formulation.

Cats that live in the southeastern and upper midwestern should consider use of a preventative.



Claws and Paws Veterinary Hospital

Feline Heartworm Disease
Atkins, Clarke E. DVM

Cats versus Heartworms: How Real Is the Threat?J.K. Levy
College of Veterinary Medicine
University of Florida

Feline Heartworm Disease: State of the Art 2007
C.E. Atkins
College of Veterinary Medicine
North Carolina State University


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