How common are heartworms in cats?

That's a good question and one that I think has gotten lost in the shuffle over the years. The answer to the question is, no, they're not very common in cats. And there's a couple of reasons why. First off, I want to share with you some figures, just to impress upon you how much of a different disease this is in dogs and cats. First off, if you took 100 dogs and gave them heartworm disease in a lab, you would pretty much have 100% of those dogs test positive for heartworms in a matter of a few months. This is because dogs are the natural hosts for heartworm disease. Cats are not, but they can contract it. The same study was presented to me as if you took 100 cats and exposed them to heartworms; you’re probably going to get anywhere between 5 and 15 of those guys come up positive. This is because they’re much more naturally resistant to the disease.

The other thing that I always thought was interesting, in dogs, especially in larger dogs, it’s not unusual to have a considerable population, 20, 30, maybe even more than that, worms that reside in the heart of a dog. Whereas in cats, it's much smaller. One or two worms in a cat, and you typically have a pretty significant, I would argue, life-threatening infection in a cat.

It's not common for that reason. Cats are naturally resistant to it to some degree, but I would also argue that it is a much more serious disease if they do contract it.

The prevalence of heartworms in cats is not clearly known because they are not tested as often as they should be. However, they are probably less common than in dogs but more common than we think, especially in high endemic heartworm areas like Houston and Louisiana.

It's not nearly as common. Again, cats are not the normal host, so it's not beneficial for a cat to get heartworms.