Cat Heartworm Disease - Prevention & Treatment of Cat Heartworm Disease

What are heartworms?

Heartworms are a physical worm—a parasite that is transmitted by the bite of an infected mosquito. And when that mosquito bites and implants the infective larva into an animal, dog or cat, it makes its way through the tissues and ultimately will make its way to the heart where it sets up shop and matures, and then later on reproduces. So that is quite literally what it is. So the parasite name is Dirofilaria immitis is what it is if you want to look it up, but it is a true and physical parasite or worm that colonizes the heart.

Dr. Scott Broussard
The Waggin Train Veterinary Clinic

How do cats get heartworms?

Well, the same way as a dog, to be quite honest with you. So as I just mentioned, they get it from an infected mosquito. Let's back up for a second. So when a dog or a cat is infected with heartworm disease and has adults, male and female, those adults start to reproduce. Once they do that, they will produce something called microfilaria. That's what I jokingly call the baby heartworms. So when a mosquito feeds on that animal, they take in that microfilaria; it lives in the mosquito for about two weeks and ultimately becomes an infective stage larva. That mosquito now goes and bites an unprotected dog or cat, and that's how the disease is transmitted, and that's how it goes full circle.

It can not go full circle in the same animal without the bite and involvement of a mosquito, so the only way a dog or cat gets more and more heartworms is if they continually get bitten by mosquitoes who are carrying heartworms, and that's how the disease worsens.

What do veterinarians recommend as heartworm prevention for felines?

Yeah, that's a good question. I think it gets overlooked a lot, and I'm even guilty of sometimes forgetting to mention it in the room. After all, heartworms are such a well-documented scenario in dogs that here where I practice in South Louisiana, it would be bordering on malpractice if you didn't discuss heartworms in dogs because it's so prevalent.

In cats, sometimes people are not aware of it. So they're not worried about it or perhaps just because they haven't seen it before. So maybe that's why they're worried about it. But to answer your question, there are products, most of which are topical, that can be given as heartworm preventatives for cats. The ones that I more routinely use are Revolution or Revolution Plus, which is a drug called Selamectin. There's Advantage Multi, which contains Moxidectin. I think Bravecto even has a variety now. Bravecto is a flea and tick medicine, but I think now for the feline product, they've come out with one that has a heartworm preventative in it as well.

And then lastly, there are some oral types like interceptors way back, but I know they still make it, Interceptor. I think Sentinel. Certain oral heartworm products are on the market for dogs, and sometimes the small dog sizes can also be used in cats. So there are plenty of options out there. Consult with your veterinarian and try to figure out something that works for you. I am a fan of topicals because there are very few cats that I know that enjoy taking a pill regularly. So typically my choice is one of the topicals, and you don't have to fool with trying to pill the cat.

How would a veterinarian diagnose heartworms in my cat?

This gets to be somewhat of a tricky question because the disease in cats, again, is night and day different from dogs. What does that mean? So it means one or two heartworms in a cat, that's bad. It's a nasty infection. And your cat may very well show clinical signs with only one or two heartworms. Why am I telling you this? Because one or two heartworms will be very difficult to pick up on the routine screening tests that we have available to us.

We use a heartworm antigen test for dogs every day. It looks for an antigen released from female heartworms; it's very specific, and it's not unusual for a dog to have eight, 10, maybe 15, 20 worms. So there's plenty of antigens there to be detected. If you're talking about a cat that has one, two worms, which is not unusual, what if those one or two worms are not female? Well, then it's not releasing this particular antigen, so it's a challenge to diagnose sometimes, but the antigen test is probably the most commonly used. There is another test where it looks for antibodies against feline heartworms or heartworms. That one can be done, but it's kind of hit or miss. You can get a lot of false positives. All it simply means is that that cat was exposed to heartworms at some point in their life. It doesn't necessarily mean that they are actively infected by heartworms now.

So again, not a 100% black and white test. And then I would tell you the third and final way that I'm aware of. If you're really good with ultrasounds, sometimes you can do a cardiac ultrasound, and you may be fortunate enough to physically see the heartworm in the right atrium or slash ventricle in the cat's heart. Again, they don't have high numbers, so it would have to be the perfect storm for that to happen, but that is a third alternative to be able to diagnose heartworms.

Why is early detection and diagnosis of heartworms so important for my cat?

Early detection and diagnosis of any disease would always be necessary. If I could potentially reword that question, I would say, why would early prevention be important? Because if your cat already has heartworms, the treatment options are extremely limited. I'll just be honest. It often carries a fairly poor prognosis if you do diagnose a cat with heartworm disease. Prevention, that's the old expression, "An ounce of prevention is worth a pound of cure." I think the guy that did it was a parasitologist who worked with feline heartworms, to be honest with you. No. I'm kidding, but it is. It's just much more virulent, but that's not the right word. It's just a much worse disease in cats than it is in dogs. So preventing it is paramount. And if you live in an area that has prevalent mosquitoes, which pretty much anywhere in the Gulf Coast area or the Southeastern United States, you can say if mosquitoes are a big problem in that area, it's just safe and better medicine to put a cat on heartworm preventative, whether they're inside or outside because that's the other thing I hear a lot. "Well, my cat's inside. He doesn't need it."

Well, if you've ever had a mosquito in your house, I think your cat needs heartworm prevention.

If you still have other questions and you'd like to reach out to us, you can call us directly at (337) 223-9581, you can email us, or you can reach out on Facebook. But please do reach out, and we'll get back to you as fast as we can.

Cat Heartworm Disease - FAQs

Dr. Scott Broussard
The Waggin Train Veterinary Clinic

Are heartworms common 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.

What are the complications of heartworm disease in cats?

Respiratory issues—again, being a more serious condition in cats and how it normally presents, I guess you could say similar to dogs, it takes fewer worms to cause these. That's the most common thing that I see. A cat that might come in for hacking, coughing, maybe even open mouth breathing, or perhaps poor color. Maybe the cat was running around playing or just jumping around a typical day, and all of a sudden just collapsed, acute collapse. It usually presents as either cardiovascular or respiratory signs in a cat.

Every once in a while, you'll see vomiting, although I personally have not seen a cat come in for vomiting and then later be diagnosed with heartworms. It's always been the respiratory signs that I have picked up on.

Are there side effects to the medication used to prevent cat heartworms?

In my experience, I'm going to say no, because again, most of the medications I'm using to prevent are combination medicines that also do fleas, ticks, ear mites, heartworms, intestinal worms, and those kinds of things. I use things like Revolution, Revolution Plus, and Advantage Multi for Cats. Those are all things I've used. Full disclosure in answer to that question, yeah I have seen some cats that don't like it when you put it on. They act very irritably, and they may even get a little patch of hair loss in that area because you're putting it on the back of the neck. I've seen those kinds of side effects, but it's not specific to the heartworm preventative that's in it. Many of those products may be alcohol-based because that helps them to absorb through the oil layer in the skin and be absorbed in the bloodstream. I think more side effects have to do with the liquid itself or the carrier that the drug is in, and perhaps not the drug itself.

Any time you put a chemical in or on an animal, you always have the risk of there being a reaction to that animal, but it's not something that I routinely see in cats.

Have you ever treated a cat with heartworms?

I've tried. I don't like to be grim, but I'm going to be honest with you, my experience with cats that come in and we can confirm a diagnosis, it very seldom ends well for that cat, in my experience. So, again, that's why I'm saying preventing it is so much more effective and wise to do, rather than playing Russian Roulette with the possibility that they might get it.

To try to answer the question perhaps a little bit more accurately, yes, I've attempted to put animals on, say Prednisone, or things like that. But, unfortunately, it usually has a very limited effect. So you want to prevent this disease in cats before it ever gets a foothold because your treatment options are very limited.

One final thing I'll add, anybody that's had a dog that's perhaps had the disease, maybe even was treated for the disease, that drug is not effectively labeled, nor used for cats. It's just a much worse scenario with cats if they do contract it. So do your best to prevent it. Choose whatever vet product you and your veterinarian discuss and what you think works best for your cat, but prevention is worth every bit of treatment down the road. Believe me; you don't want to go that route.

If you still have other questions and you'd like to reach out to us, you can call us directly at (337) 223-9581, you can email us, or you can reach out on Facebook. But please do reach out, and we'll get back to you as fast as we can.