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Heartworms in Cats and Dogs

Mindy Norton

Heartworms can be life-threatening for pets.  Most pet owners know they can give their dogs a preventative periodically to protect them from heartworms.  But cats are also at risk and need to be protected, as well.


Heartworms? In cats?? Most people think heartworms are a dog problem, not a cat problem. Unfortunately, that’s just not so. Cats can get heartworms; and as with dogs, it can be fatal to our feline friends as well.

The method of transmission is the same for both dogs and cats. A mosquito bites an infected animal, then bites a healthy animal, transmitting the microscopic heartworm larva. As the larva begin to develop into worms, they enter the bloodstream where they continue to grow, interfering with the animal’s circulatory system. In dogs, heartworms can grow up to a foot long and live about five years. In cats they tend to be smaller, maybe six inches or so, and live for only a couple of years. In addition, an infected dog may have thirty heartworms or more, while an infected cat may have only a handful. The difference with cats is that their heart and blood vessels are much smaller, so those few worms can cause major problems. In fact, just one or two heartworms could kill a cat.

One advantage for dogs is that heartworm infection can be treated. Not so with cats – there is no prescribed treatment that is considered safe and effective for feline heartworms. Complicating the issue is that it’s more difficult to diagnose heartworm infection in cats. Experts think that may be one reason for the lower reported incidence of heartworms in cats as compared to dogs.

Heartworm disease has been found in pets in all fifty states. The good news is that heartworms are completely preventable for both dogs and cats. You can choose between a chewable product or one that is applied topically, but you must have a prescription. Be careful to choose a product that is approved for cats; do not use canine heartworm preventative on your feline friend. And before using any product, have your veterinarian test your pet for heartworms first, because administering the preventative to a pet that’s already infected could be fatal for the animal.

Whether your pet stays inside all the time or spends time outdoors, once again a little prevention can help to keep your best friend healthy, when you’re speaking of pets.


Mindy Norton has been “Speaking of Pets” on Alabama Public Radio since 1995.
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