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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.

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