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6 Things You Didn’t Know About Heartworm Disease in Cats

By Thursday April 13th, 2017Blog

“Cats are not small dogs,” as we are taught in veterinary school, and never was this folksy piece of wisdom more true than when considering the differences between the way that nasty parasite, the heartworm, affects both species. Do you need to worry about heartworm disease in your cat? The answer is that you probably should, at least consider whether your cat could be infected based on your cat’s lifestyle and where you live. Read on to get educated about heartworm disease in cats.

1. YOU DIDN’T KNOW CATS COULD GET HEARTWORM DISEASE

Let’s start with probably the biggest one. Most pet parents aren’t even aware that cats could get heartworm disease. Everyone one seems to know what a big problem it is in dogs, and how important it is to protect your dog with a monthly dose of preventive, but the word is definitely not out about cats.

Why is that? It’s likely because cats get heartworm disease at a much, much lower rate than dogs do. It’s believed that less than 25% of the immature heartworms (the larva) reach the adult stage in a cat. So the odds are in favor of our feline friends, but even a small chance of heartworm disease is a bad proposition in cats.

2. CATS ARE LESS SUSCEPTIBLE THAN DOGS, BUT THEY STILL GET HEARTWORM DISEASE

Studies show that in heartworm prevalent areas, cats get heartworm disease at only 5 – 20% of the rate that dogs do. But they definitely still get it, and some experts suspect that many cats remain undiagnosed, with their symptoms being attributed to allergies or asthma.

If you live in an area where heartworm disease is prevalent – discuss with your veterinarian whether your cat should receive a monthly heartworm preventive.

3. THERE’S NO TREATMENT FOR HEARTWORM DISEASE IN CATS

The drugs that we use to treat heartworm disease in dogs are awful, but effective. They cause pain at the injection site for days, and the dog must be cage-rested for a period of time after administration, in order to make sure that the dying worms don’t form a clot in the arteries. But at least we have a treatment that cures heartworm disease in dogs.

In cats, we aren’t so fortunate. There is significant risk associated with using these drugs in cats, and studies have not shown that doing so increases the chance of a favorable outcome for the cat. So we are left with treating the clinical signs of the infection, most of which are centered around the respiratory tract, where the heartworm infestation causes severe inflammation, a syndrome known as Heartworm-Associated Respiratory Disease, or HARD.

4. ONE ADULT HEARTWORM CAN CAUSE SUDDEN DEATH IN A CAT

Dogs typically don’t show the signs of a heartworm infestation – typically coughing, respiratory difficulties, and exercise intolerance – until the number of worms in the body is quite significant. When dogs have only the heartworm larva in their blood, and no adults are yet present, we usually detect it, because running a heartworm test is a much more common occurrence in dogs than it is in dogs.

Because cats develop such an intense inflammatory response to even one heartworm, they tend to be seriously ill even with a relatively low number of adult worms. When they develop symptoms, they are usually respiratory in nature, including coughing and respiratory difficulties, but cats with heartworm disease also display frequent vomiting. Because of this, any cat with chronic vomiting should be tested for heartworm disease.

5. INDOOR CATS ARE AT RISK, TOO

In one study of heartworm-positive cats in Italy, 19% were indoor-only cats. Because cats get infected with heartworm disease through mosquito bites, it stands to reason that even indoor cats can be at risk, due to the fact that mosquitos can and will get indoors. Unlike intestinal parasites and external parasites like fleas and ticks, which tend to be present only outdoors, indoor cats are still at risk for heartworm disease because of the way it is transmitted.

6. IT’S NOT EASY TO DIAGNOSE HEARTWORM DISEASE IN CATS

Most veterinarians recommend testing their canine patients for heartworm disease once a year. And subsequently, most veterinarians recommend that dogs be given heartworm preventive every month of the year, although sometimes that recommendation varies, depending on the prevalence of mosquitos in that area.

But most cats don’t get routinely tested for heartworm infection, and even if they test positive on the “screening” test, it doesn’t necessarily mean that they are infected with heartworm disease. The test can come up positive if the cat has been exposed to heartworm disease, so more tests must be run to confirm the infection, including additional blood tests and also echocardiogram (ultrasound of the heart).