Cat heartworms are a growing concern, particularly since the incidence of dog heartworms continues to rise. Is your cat protected against heartworm disease?
CAT HEARTWORMS TRANSMISSION
To become infected, a cat must live in an area that has infected dogs, and with mosquitoes that have a taste for both dog blood and cat blood. Wildlife also serves as a reservoir for the disease so coyotes and raccoons could put your pets at risk. Heck, the coyotes come up onto my back patio! Even though Magical-Dawg is negative for the disease and takes preventative, Seren-kitty could get heartworm from a single mosquito biting a coyote and nailing her before I could swat the sucker.
That’s right, I said it. A cat doesn’t have to go outside to be exposed. Exclusively indoor cats also get heartworm disease. They may even be more susceptible, yikes!
HOW CAT HEARTWORMS ARE TRANSMITTED
Mosquitoes ingest baby heartworms (microfilariae) when taking a blood meal from an already infected animal. The immature parasites spend about three weeks developing inside the mosquito and migrate to the mouthparts of the insect. When the mosquito again takes a blood meal, larvae are deposited upon the skin and gain entrance to the new host’s body through the bite wound left by the mosquito. Once inside the body, the immature heartworm undergoes many more molts and development stages.
CAT HEARTWORMS SYMPTOMS ARE H.A.R.D.

Outdoor cats exposed to mosquitoes increase risk of contracting heartworm disease–but even indoor kitties can get infected.
The larvae are carried by the blood through the heart to the cat’s pulmonary arteries which almost immediately become enlarged and inflamed. They usually die in cats in about 9 months (they can live 5 years in dogs!) and cause severe inflammatory respiratory problems when they die. This has been described as heartworm associated respiratory disease (HARD).
Feline airways become thickened, stiff, and inflamed. Cats with asthma symptoms—open-mouth breathing with blue gums—may in fact be suffering from heartworm disease. Frequent vomiting also can be a sign of feline heartworm disease. “The third unfortunate sign we see is the cat is fine this morning, and dead this afternoon,” says Dr. Graham.
CAT HEARTWORMS TESTS
Current tests don’t detect all feline heartworm cases. Antigen tests identify the presence of adult female worms. That means cats could have immature worms present, or an adult male, and appear to be safe. Antibody tests can detect very early infections by immature worms–fantastic for our dogs!–but half of all cats that have worms don’t have antibodies against them. Additional chest radiographs and echocardiograms may be needed when heartworm infection is suspected.
A single heartworm can kill the cat, and there’s no cure or treatment for feline heartworms. Instead, veterinarians suppress the inflammation in the lungs and make it easier to breathe using such drugs as prednisone, bronchodilators, and doxycycline. Infected cats usually are put on heartworm preventive so they don’t get any new worms that further complicate their care.
Preventing Feline Heartworms
While diagnosis is difficult and treatment virtually impossible, there are preventive products for cats. The American Heartworm Society provides guidelines and the latest research on its site. They recommend all cats should be on preventative, year round. Start kittens at 6 to 8 weeks of age–there are products that not only prevent heartworms but also control other parasites like fleas so you’re multi-tasking and keeping kitty safe. It costs pennies a day to protect my dog and cat, compared to the expense of treating an infection.
Losing Shadow-Pup or Karma-Kat to heartworms is not a price I’m willing to pay.
How about you? What sorts of preventatives to you give your fur-kids? Fleas and tick stuff? Heartworm prevention? Do you prefer the “natural” route or have suggestions how to get the cats to accept “what’s good for them?” There are liquid alternatives and spot ons for some of these preventions. What works best for your pets?
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Amy Shojai, CABC is a certified cat & dog behavior consultant, a consultant to the pet industry, and the award-winning author of 35+ pet-centric books and Thrillers with Bite! Oh, and she loves bling!
A nasty-sounding worm. Fortunately we don’t get so many of these in the UK, I think. There’s some interesting information about tapeworm and fleas on http://www.CatWormsSymptoms.com, if it’s relevant.
Hi Charles,
Yes, cats DO get heartworms in the UK and dogs, too. They’ve been found around the world, unfortunately. I understand Italy has a big problem because of mosquitoes and water.
Thanks for the link to the intestinal worms issues. Here if a kitty is on some of the more common flea preventives–and some of the heartworm preventives too–they also prevent intestinal parasites.
That is a scary worm! Very interresting article, I’ve only heard of it before, Have you heard if it’s common in Europe/Scandinavia? As I live in Sweden and am concerned about my cat. I will also try to check it up myself, but maybe you know.
Hi Lotta, you’d have to ask your veterinarians. From what I can tell, the incidence of canine heartworms is increasing in Europe possibly from importing pets from outside of the country.