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Heartworms in Cats

Heartworm disease in cats is very different from heartworm disease in dogs. The cat is an atypical host for heartworms, and most worms in cats do not survive to the adult stage. Cats with adult heartworms typically have just one to three worms, and many cats affected by heartworms have no adult worms. While this means heartworm disease often goes undiagnosed in cats, it’s important to understand that even immature worms cause real damage in the form of a condition known as heartworm associated respiratory disease (HARD). Moreover, the medication used to treat heartworm infections in dogs cannot be used in cats, so prevention is the only means of protecting cats from the effects of heartworm disease.

The following is a transcript of an interview with Dr. Jennifer Lavender, co-founder of Metro Paws Animal Hospitals in Texas:

Do cats get heartworms?

Yes cats absolutely get heartworms. Most people think heartworm is mainly a dog’s disease but cats get them too.

What cats are at risk?

The risk of kittens getting heartworm disease is equal to that of adult cats and both indoor and outdoor cats are at risk.

How do cats get heartworms?

Cats get heartworms from mosquito bites. The mosquito bites the animal and when the proboscis, the needlelike structure on the front of the mosquito’s head, penetrates the skin, microscopic marble forms of the heartworm larvae are injected into your cat’s skin. It’s at this stage you might see some symptoms, like difficulty breathing or coughing – and most worms die at this stage. But the worms that don’t die travel through the tissues, eventually to the bloodstream where they start to mature and eventually develop into spaghetti-size adult worms in the heart and most likely live undetected for a couple of years. ) “Heartworm disease” is a misnomer because it mostly affects the lungs and not just the heart.

If a cat doesn’t go outside, it’s safe, right?

Not going outside isn’t enough to protect your cat from heartworms. I always tell people if that’s the case I'm going come live at their house because I definitely have mosquitoes in my house from time to time!

How do you diagnose heartworms in cats?

One of the scariest things about heartworms in cats is we don't have a good blood test for heartworms in cats like we do with dogs, so diagnosing heartworms is very difficult in cats. Signs are often mistaken for feline asthma, allergic bronchitis or other respiratory diseases.  If your cat was to have an X-Ray or an ultrasound, even those modalities don't typically show the heartworm. There is a form, a structure on the female worm that will show up on an ultrasound. The male worms don’t show up at all and then we have similar limitations with a blood test. So what happens in cats, because they only have a one or two-worm burden, much lower worm-burden than a heartworm-positive dog, we can really miss those infections because of this limitation of the test. So right there we've got a huge problem not being able to diagnose it.

What are the symptoms of heartworms in cats?

The number one presenting signs for dogs with heartworms is coughing or exercising intolerance. Unfortunately, the number one presenting sign for cats with heartworm disease is sudden death where that worm breaks off and then they have a sudden thrombolic event, much like a stroke. So with cats, it's a much more serious condition in the heart. There are also new studies coming out that are showing immature worms may also cause inflammation in the lungs which can be very damaging to the cat.

What are treatment options for cats with heartworms?

So once again highlighting the difference of heartworms in dogs, we have no treatment for heartworms with cats. And now we have a disease that I can't test for; I can't treat if they get it; and the number one presenting sign is sudden death.

Are there ways to prevent cats from getting heartworms?

The only thing I have in my arsenal to try and protect kitty from heartworms is prevention. Prevention, prevention, prevention. That comes in several different forms. There are the topical forms that cover fleas as well, that could be given monthly. There's also an oral monthly heartworm prevention but it is so, so, so important to have cats on heartworm prevention because like I said before we can't test for it, we can’t treat it, and the consequences to your cat can be fatal.

Are the prevention treatments safe for cats?

The anti-parasitic drugs are tailored to neurotransmitters that are only found in the invertebrate parasite that we’re trying to treat them for, so they're very, very safe for dogs and cats.

Does the prevention treatment do anything to eliminate heartworms if they’re already present in a cat?

No, it does not.  And you wouldn't want it to. Eliminating adult heartworms is risky and needs to be done with medications that cause the worms to die very slowly. HOWEVER, if a cat is positive for heartworms, the prevention keeps them from getting any MORE heartworms from the environment. The heartworms the cat already has cannot make babies that grow into new worms. Babies heartworms MUST exit the cat and pass through a mosquito to continue to mature. This makes heartworm prevention extremely important, even in a heartworm positive cat.

 Anything else you’d like to add about cats getting heartworms?

Just a reminder that all cats are susceptible to heartworm disease. We have no test or treatment for this potentially fatal disease for cats.  The key is PREVENTION!


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