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Woof Wednesday: Heart-to-Heart About Doggy Heartworms

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Puppies need heartworm preventive starting at 6-8 weeks of age. Copr. Paul Loades

I hate mosquitos not only because they’re itchy aggravation, but these nasty vampires spread deadly heartworm disease. That can make your dog sick or worse—it could kill her. Dogs are the natural host–but they also can affect cats–and heartworms have been a problem at least since 1922 when they were first discovered. Today heartworms are found all over the world. They affect baby dogs, too, like this stunning puppy picture from Paul Loades. And adult dogs like Dan Ciminera’s handsome doggy friend, below, are at even greater risk.

The heartworm Dirofilaria immitis belongs to a group of parasites called filarids, and is a type of roundworm. They live in the right heart chambers and pulmonary arteries—the lungs—of infected dogs. As you can imagine, lungs and heart filled with worms can damage and interfere with normal organ function. You won’t be able to tell if your puppy has heartworms. You can’t see them the way you can fleas or ticks. And your dog won’t even act sick until she’s been infected for quite a while. Learn more about how heartworms affect your dogs and are treated in this article about heartworms. 


Don't risk it--our dogs are too precious so give preventive all year long! Copr. Dan Ciminera


Most dog owners understand the seriousness of keeping their dogs on heartworm preventative—and it’s even more important now because the only FDA-approved treatment Immiticide (Merial) is unavailable. Dogs diagnosed with heartworms instead are being managed with the recommendations from the American Heartworm Society .

It’s important that pet owners remain faithful and give preventive medication on the prescribed schedule, too. Just being a few days late may open a window for infection. But there have been a few cases where dogs became infected even though they were given preventative without fail. Researchers suspect that some heartworm populations become resistant to the drug—so a new study has been launched.


Dr. Mark Rishniw, a genetic researcher at Cornell University requests veterinary practitioners from across the United States collect and send to him blood samples containing microfilaria and/or adult heartworms. A genetic survey hopefully will offer insight into the drug resistance issues being described. Veterinarians can email or call Dr. Rishniw for additional information at or 916-275-1650.

The president of the American Heartworm Society, Dr. Wallace Graham, addresses questions about prevention, treatment and more in my latest radio interview with him. Find out what you need to know to keep your cats and dogs safe from heartworm disease in PET PEEVES, HEART-TO-HEART ABOUT HEARTWORMS.

I love hearing from you, so please share comments and questions. Do you have an ASK AMY question you’d like answered? Stay up to date on all the latest just subscribe the blog, “like” me on Facebook, listen to the weekly radio show, check out weekly FREE PUPPY CARE newsletter, and sign up for Pet Peeves newsletter with pet book give-aways!

Feline Friday: Heart-to-Heart About Heartworms

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Anubis portrait

Anubis, a gorgeous kitty who shares life with Karyl Cunningham.

I just completed an interview for Pet Peeves radio show with Dr. Wallace Graham, the president of the American Heartworm Society (stay tuned—I’ll post the link when it goes live). Do you give your cat heartworm preventative? Yes, CATS can get the disease. Seren eats her monthly treatment like a treat. Thank heaven’s for that or I might risk loosing fingers when I pilled her!


An intermediate host, the mosquito, is necessary to transmit the disease. Although here in Texas we’re in the middle of a drought, you can bet mosquito-vampires find a way to continue to spread their lethal cargo.

Dogs are the natural host, but cats also get heartworms yet don’t develop the same kind of disease. Feline heartworm disease remains an invisible illness despite having nearly twice the incidence of feline “aids” or leukemia virus. The incidence varies across geographic regions but runs about ten to twenty percent that of dogs. Here in Texas, that means feline heartworm disease is much more common where the dog disease tends to be relatively high. And in the Mississippi Delta region there’s a virtual epidemic in dogs—and cats are affected more often, too.

Dr. Jeffrey Klausner, a veterinary internist and senior vice president and chief medical officer (CMO) of Banfield Pet Hospital says, “In our own analysis of data from more than two million dogs and almost half a million cats, we determined that heartworm disease is among the top three disease risks for pets in the southern United States. Education and awareness are vital to reducing this risk.”

Outdoor cats are at highest risk for parasites--even though they LOVE life on the outside! How do you make the outside safe?


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. Dr. Graham says that 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. Dr. Graham mentioned he’d recently diagnosed a couple of exclusively indoor cats in his clinic in Corpus Cristi. Yikes!

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.


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.


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.


Even pampered show cats aren't immune.

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. And these days, the dog treatment for heartworms is temperarily unavailable.

Losing Magical-Dawg or Seren-Kitty 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?

I love hearing from you, so please share comments and questions. Do you have an ASK AMY question you’d like answered? Stay up to date on all the latest just subscribe the blog, “like” me on Facebook, listen to the weekly radio show, check out weekly FREE PUPPY CARE newsletter, and sign up for Pet Peeves newsletter with pet book give-aways!