Cats vs. Heartworms: Battle of the Century

Cats vs. Heartworms: Battle of the Century

It was 1921, almost 100 years ago, when the first heartworm was discovered in a cat. The fact that cats could acquire this dangerous parasite received little attention, however, until three-quarters of a century later. How did feline heartworms manage to sneak along under the radar for so long? The truth is that they’re a bit too wily for us simple human beings.

Diagnosing this infection in dogs is very easy. The canine blood test yields pretty black-and-white results within about 10 minutes. A cat-specific blood test has also been developed, but it doesn’t always tell the whole truth. Infections with only a few worms are less likely to be detected, and cats can only harbor 1-5 worms. Many infestations with adult heartworms thus go undiscovered. To complicate matters, we now know that cats begin to suffer serious health issues before the worm even reaches maturity, and that’s before the test could even begin to register a positive. A different type of blood work is meant to reveal whether exposure to baby worms has ever occurred, but it’s often foiled by the complexity of the feline immune system. X-rays of heartworm-infected cats don’t help!

Cats with heartworms may exhibit various symptoms, but none of them are very specific. As long as your cat doesn’t die suddenly from this serious infection, coughing, vomiting, and weight loss are the most common signs. Vomiting and weight loss are caused by a thousand other kinds of illness, so these items won’t shed any light on the diagnosis. Coughing cats are most often treated for asthma, but many veterinarians have begun to question this pattern. What if our asthmatic patients have been secretly harboring cardiac parasites all along? Disturbing thought for the doctors!

But here’s the sad reason why none of that really makes a difference: there’s no treatment. The medicine used to remove heartworms from dogs is far too dangerous for cats. The best we can do for these patients is attempting to reduce the discomfort, trying to control the cough. Drugs are used to stifle the immune system until it no longer recognizes the parasite. Under this regimen, we hope that the angry inflammation in the lungs will subside. The parasites themselves will have to stay—inside your pet’s heart, long term.

So in the battle over the cat, it would seem that the heartworm has just about beat us… or has it? True, our current battery of blood tests and x-rays offers little in the way of clarity. Even after we’ve achieved a definitive diagnosis, the parasite can never be removed. But we do have one really big gun. It’s sitting there on your veterinarian’s shelf—not just one, but multiple kinds of easy-to-use medicine that are guaranteed to protect your cat. Just follow the directions on the package once each month, and you’ll be blasting these crafty parasites to bits. If you just take action early enough, you won’t ever have to navigate the minefield of feline heartworm disease. And I’d say that’s a big win.

Dr. M. S. Regan