Cats Get Heartworms Too

February 6, 2012

When I was notified that this month’s edition would be about Valentines and Groundhog day, two things came to my mind, neither of which were romance or global warming. Instead, I immediately thought of hearts. The real things that pump our pet’s blood, not the valentine kind. I also thought of Dachshund and their genetic urge to hunt the groundhog. In the end, I decided to focus on hearts, especially cat hearts, because I have a pet (no pun intended) peeve: Too few cat owners know or understand the grim reality of heartworms in cats. It seems everyone knows that dogs can get heartworms. They diligently give their dog his heartworm pill once a month to prevent this deadly disease. But what about our cats?
When I graduated from veterinary school too many years ago, we thought that it was extremely rare for cats to get heartworms. This turned out to be terribly wrong. The truth was that cats were hard to test for heartworms, so we simply didn’t know that they were dying from this disease.
Let’s start with some background information, so you can understand how heartworms affect cats. Heartworm larvae enter the cat’s body while a mosquito is feeding on the cat’s skin. Unlike the dog, the cat is not a natural host for the heartworms and the cat tends to mount a massive immune response to these migrating larvae. Thus, very few baby heartworms make it to adulthood in the cat’s heart, but the inflammation from this immune attack is quite detrimental to the cat’s well-being. If a larvae does make it to the heart, the ensuing adult worm wreaks havoc. While dozens of adult worms can develop in a dog’s heart, cats usually only develop one to five. But, even one worm is absolutely deadly to a cat.
Symptoms of heartworms in cats are different from a dog as cats develop more of a lung disease that shows up as respiratory distress, chronic coughing or vomiting. Feline heartworm disease is often misdiagnosed as asthma. Some cats with heartworms die a very sudden death when the body mounts a massive immune reaction to a heartworm.
In cats there are two phases where the disease can show symptoms. The first is when immature worms reach the blood vessels in the lungs. Even these tiny worms casue inflammation that interferes with the cat’s ability to breathe. The second phase can occur when a worm dies. At this time the worm loses its “protective coating” and the body recognizes it as a foreign body. The inflammatory reaction mounted when a worm dies in a cat’s lung is basically anaphylactic shock – or a massive allergic reaction that can result in sudden death.
The test for heartworms in dogs is fairly uncomplicated and simply picks proteins from female adult heartworms, but since cats rarely develop a full grown heartworm, there may be too few worms to produce a positive test. Therefore no single test for heartworms in cats is reliable. The American Heartworm Society recommends that cats get two types of tests, both an antibody and an antigen test. Chest x rays and echocardiograms may also be necessary.
There is no way to rid a cat of heartworms. Killing the worms with drugs like we do with dogs is too dangerous because of the massive inflammatory reaction that cats have to dead worms. Therefore all we can do is try to control the inflammation and wait out the heatrworm’s lifespan of 2-3 years. Some cats make it and some don’t.
The good news is that heartworm infection in cats is 100% preventable! So why aren’t all cats on heartworm prevention? I just don’t understand this. Heartworm prevention can be easy to give to a cat, as it comes in yummy chewies or topical applications, so you don’t have to chase your cat around to give a pill every month. There simply are no good excuses, so ask your vet how you can protect your cat’s heart today.

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