Cat Heartworm Disease - Diagnosing and Treating Cat Heartworm Disease

What is heartworm in cats?

Heartworm in cats is a little different from heartworm in dogs. Heartworm tends to be a dog parasite, although it can infect a cat. But, cats do something different when they get infected because the cat is not its natural host. Cats have more asthma-like symptoms as these worms are migrating through their body, and most of the time, the cat self-cures this disease because they're not the natural host or reservoir for it. It's not as common in cats as in dogs. But that's hard to say because there's not a great test for cats too. So, and it may be that cats are significantly under-reported, so to speak, because we have trouble finding it in cats.

Dr. Ashly LaRoche
Animal Hospital of Statesville

How do cats get heartworm?

Cats get heartworm by being bitten by a mosquito, just like in a dog.

What do you recommend as heartworm prevention for cats?

There are some labeled pill-forms of heartworm prevention that also do intestinal parasites, just like for dogs. And there are also some topical products: Advantage Multi and Revolution are the two big ones that prevent heartworm in cats. And we tend to do better with the topicals because many people can't get their cats to take a pill.

How do you spot heartworm symptoms in a cat?

Heartworm symptoms in a cat are very asthma-like, so you're going to see a cat that coughs, and open-mouth breathes or pants. Panting in a cat is not a common thing unless they're stressed, or they have the advanced disease of the lungs, so panting or open-mouth breathing is one of the biggest things that you'll see. Other times you'll see them get a cough or labored breathing. And oddly enough, vomiting is a big sign of heartworm in cats.

How would a veterinarian diagnose heartworm in a cat?

Cat heartworm diagnosis is challenging, and that's because, most of the time, the damage done in a cat is from the migrational state or the larvae. And what that larvae do is migrate, and they cause a tremendous immune response in the cat. The cat's immune system does not want them there, and it's very exuberant. As those worms arrive in the lungs, the immune system destroys them, but it's causing so much inflammation in the lungs that they're having this horrible asthma reaction.

Heartworms in cats rarely develop into adult worms. And if it does, there's usually only a couple of worms, and a lot of times our male worms, oddly enough. Hence, when we are testing dogs for heartworm, we're testing adult female worms. That's simply not the case in cats, as they really don't have them, so they'll test negative even if they have an infestation.

If we suspect that a cat may have heartworm at any stage, we'll sometimes recommend a heartworm test. It's the same test that we use in a dog, an ELISA blood test. We'll do a microfilaria screen; although cats rarely have microfilaria, we'll still screen them for it. And one of our great diagnostic tools in a cat is X-rays. We look at X-rays of the chest to look at their pulmonary arteries because cats can have immature heartworms and still test negative for all the conventional tests we use for dogs.

Why is early detection and diagnosis of heartworm in cats important?

That's very important, the reason being once they've had heartworm and they've had lung damage, it's very permanent. It's a permanent asthma-like situation in the cats. Also, if you have worms become adults, the cat's heart is tiny, and they get 12-inch worms that coil around in there. One worm can be devastating to a cat. Also, once they get to be adult worms, there is no conventional treatment in cats. Those worms only live a couple of years in the cats, and then they die because the cat is not the natural host. And unfortunately, once the worm dies, the inflammatory reaction set off as those worms decay causes the cat to die with it. Heartworm prevention in cats is a must because once they get an infestation and it reaches adulthood, it's fatal for the cat most of the time.

If you still have other questions and you'd like to reach out to us, you can call us directly at (704) 872-3625, you can email us, or you can reach out on Facebook. But please do reach out, and we'll get back to you as soon as we can.

Cat Heartworm Disease - FAQs

Dr. Ashly LaRoche
Animal Hospital of Statesville

What is cat heartworm disease?

Cat heartworm is an internal parasite that causes significant lung damage. Cats become infected by being bit by mosquitoes.

What is an internal parasite?

It's a parasite that lives inside. A mosquito injects these worms into the body of the cat, and it migrates toward the lungs.

Can a cat pass on heartworm to another cat, a dog, or a person?

No, all heartworms have to go into a mosquito for part of their life cycle before being transmitted to another animal.

What is the cycle of the heartworm, and how is that information important to a cat?

The heartworm cycle in a cat is when a mosquito bites the cat and injects a baby worm into the cat's skin. These worms then migrate through the skin into the bloodstream, and they arrive at the lungs, and that's when all the damage is done. Months later, when the worms start arriving at the lungs, the cat develops an intense inflammatory reaction to destroy these worms before they continue to mature. The cat has these asthma-like symptoms—coughing, open mouth breathing, vomiting, and labored breathing in general.

How does a cat's lifestyle affect their risk for heartworm?

Cats that roam and are outside more are a little more at risk of becoming infected with heartworm. It's much less than the risk of a dog. Even so, because heartworm disease is invariably fatal for a cat if it reaches maturity, prevention is paramount.

What's a sign that my cat has heartworms?

Weight loss, open mouth breathing, coughing and labored breathing, and often vomiting. Cats tend to vomit with many different diseases.

Cats develop symptoms much earlier than dogs because the immature stages arrive in the lungs earlier than in dogs. Dog symptoms are more geared towards adult worms being present. It's the immature stages, the earlier stages, that cause problems in a cat. Sometimes a few worms will make it to adulthood, and that's not a good scenario when that happens.

Is heartworm painful for a cat?

Heartworm tends to cause asthma-like symptoms, so the cat can't breathe. They're not perfusing, so they're very panicked. Some of their tissues may be a little painful because they're not perfusing, the pins and needles, perhaps, but I'm not sure.

How is a cat tested for heartworm?

Typically, if we suspect a cat has heartworm, we will recommend a test just like in a dog. Most of the time, it comes out negative because, once again, that test tests for adult heartworms, which it's not usually adult heartworm that causes a problem in a cat. There aren't tests out there for immature stages. We sometimes test for antibodies. However, though they can develop antibodies a couple of months after infection, they are very transient. They go away really quickly, so we have a short window to catch them. That only means exposure and not necessarily that the cat is continuing to be infected as well. We will often look at x-rays, and we can see changes in the lungs that are highly suspicious of heartworm.

How often should my cat be tested for heartworms?

We only recommend testing when we think the cat has heartworm. Routine testing is typically not done, probably because there's no treatment for it once the cat has adult heartworms. They don't have microfilaria, which is the baby warm circulating in the blood, so all heartworm preventatives are safe for them. We recommend prevention in cats.

In a symptomatic cat, a sick cat, and we suspect heartworms, then we're probably going to get an x-ray, we screen for antibodies. And do the ELISA antigen test as well.

If my cat's on prevention, do I need to have them tested yearly like dogs?

No, because they don't have microfilaria, we can go ahead and put them on preventatives. They so rarely test positive because they almost never get adult worms, so yearly testing is not recommended.

How is heartworm prevented in cats?

Typically, there are some pills that you can give kitty cats like you do dogs, that are labeled for a cat but are a bit different. There are also topicals. The vast majority of people use the topicals that you put on the skin. These prescription medicines prevent the dog or the cat from getting infected, to begin with. That's the key with a cat, to prevent them from getting infected.

How effective is heartworm prevention in cats?

Heartworm preventions are 95% effective or more if administered properly and given regularly.

Are there any holistic or over-the-counter treatments for heartworms?

There are not. Vector and mosquito control can help, but still, those preventative products are essential. A lot of those preventative products also keep fleas and ticks away and help treat intestinal parasites.

Can I do anything in my cat's environment to reduce the risk of heartworm?

Preventing standing water is essential. You can use area mosquito sprays and things like that, and they are safe if you follow directions. Anything you can do to keep the mosquito population down in the area helps. Usually, that is combated by avoiding standing water in those areas, dumping standing water from your flower pots, and other things like that.

What should I do if I miss a dose of my cat's heartworm prevention?

If you miss a dose, keep going. As soon as you realize you've missed it, go ahead and give the cat another one and just go on their regular monthly routine. If they are not showing any symptoms, great, we don't go any further with that.

If a cat does get an adult heartworm or two, there is no treatment available. They can't get the conventional treatment that dogs do. The medication is somewhat toxic in a cat. Then as the worm dies, the cat often dies as well, which is why prevention is so vital. If infected, the cat develops chronic asthma-like symptoms once infected with heartworm, and that lasts for life. That's treated with things like corticosteroids and bronchodilators as needed, but there's permanent damage done to the lungs.

Can prevention be used to control heartworm in a cat or to cure it?

It can prevent it. I don't think the research has been done out there yet to see if chronic prevention eventually treats or kills the heartworm. Having an adult heartworm die is often fatal to the cat, so we can't let anything reach adulthood by prevention.

Say my cat has tested positive for heartworm. What would the next step be?

X-rays, monitoring, and bracing owners that this cat may go into a fatal crisis when this heartworm dies (they live about two years). There's not a whole lot you can do to prevent that. Despite the best of efforts, those cats die.

Sometimes specialists can surgically/manually remove heartworm, but it's costly. How often it's done, I'm not sure. It's probably a pretty risky procedure, too, I would think.

Is early detection and diagnosis of heartworm more difficult in cats?

Yeah, it's challenging in cats. Cats often test negative for everything, but they're infected with heartworm because it does different things in a cat. If a cat has asthma-like symptoms, and cats get asthma anyway, it's an allergic lung disease, but it can also be triggered by heartworm. It's often an educated guess. The treatment is the same as treating asthma, with steroids, bronchodilators, things like that, but we're still going to have to figure out if heartworm is the underlying cause. If we suspect heartworm, we may do antigen testing later to see if it was heartworm that caused the asthma attack, and we may never know.

The incidence in cats is much lower than a dogs because it is a dog parasite for the most part. Cats' lifestyles and things like that make them a little less susceptible as well. But it's the cat's immune system reaction to the parasite when they get infected that causes all the cat symptoms more than anything.

Are there side effects to the medications that we use in cats to prevent heartworms?

For the most part, these preventives are very well tolerated. Sometimes you'll see local site reactions where you apply the topical; they'll lose hair and get itchy. On occasion, I've had owners report cats that just don't feel well after the topical is applied. If we suspect that the heartworm preventative is causing some lethargy or depression, we'll switch products.

What are the risks if heartworm is left untreated?

If we don't prevent heartworm, the chronic lung disease in cats will eventually become resistant to treatment and become fatal. Sometimes that's the only sign that you see is death. The cat has adult heartworm, and it doesn't show any symptoms, and then the owner finds the pet deceased. That, unfortunately, is the first sign that you see with a cat.

Asthma in and of itself as an allergic problem is widespread in cats, also making it tough to diagnose heartworm in cats.

As an aside, we recommend yearly retroviral screening, which are diseases like feline leukemia and FIV, which are for a different day of discussion. But that particular test also tests for heartworm disease as well. We recommend outdoor cats get screened for those diseases, so we're inadvertently screening for heartworm as well. It helps with preparedness for what might happen in the life of that cat if it is positive.

If you still have other questions and you'd like to reach out to us, you can call us directly at (704) 872-3625, you can email us, or you can reach out on Facebook. But please do reach out, and we'll get back to you as soon as we can.