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Heartworm Disease

What is heartworm?

Heartworms are parasites that infect dogs and other animals. The worms make their home in the heart, where they block blood flow, damage the lungs, and cause other health problems. The disease is often fatal in heavily-infested dogs.


How does a dog get heartworm?

Heartworm is transmitted by mosquitoes. When carrier mosquitoes bite a dog, they inject tiny heartworm larvae into the dog's bloodstream. These microscopic larvae eventually settle in the dog's heart, where they can grow to be 30 cm (12 inches) long. When the adult heartworms produce new larvae, the larvae circulate in the dog's blood and are picked up by biting mosquitoes. The carrier mosquito bites a new victim and the cycle begins again.


What are the symptoms of heartworm disease?

There is a wide spectrum of symptoms, depending on how many worms are living in the dog's heart. Dogs with only a few worms may carry them for years without showing any symptoms. Dogs with many worms usually develop serious heart, lung, liver and kidney problems, with symptoms such as weight loss, coughing, fever, poor haircoat, and inability to tolerate exercise. Dogs with heavy infestations will usually die unless the disease is treated.


Is there a test for heartworm?

If your veterinarian feels your dog is at risk for heartworm, he or she will probably recommend a simple blood test to rule out the disease. If the initial test is positive, further tests may be recommended to confirm that your dog is infested. It is very important to confirm the dog's heartworm status before starting preventive medication or treatment.


Do we have heartworm in Canada?

Yes. Heartworm occurs in warmer regions, where summer temperatures are high enough for the worm larvae to survive inside the carrier mosquitoes. The high-risk areas in Canada are southern Ontario, southern Quebec Manitoba, and the Okanagan in British Columbia. Heartworm is also found in most states in the US.


Although it is not absolutely certain, it appears that heartworms are unable to survive at prevailing temperatures in Alberta and Saskatchewan. A few cases are diagnosed in these provinces every year, but to date they have all been dogs that have visited or lived in heartworm risk areas.


How do I protect my dog from heartworm?

With heartworm, an ounce of prevention is truly worth a pound of cure. The disease can easily be prevented with inexpensive monthly medication prescribed by your veterinarian. Heartworm disease can be fatal.  Further, treatment of full-blown heartworm disease is costly, time-consuming, hazardous, and not always successful.


If you are traveling outside Alberta with your pet, talk to your veterinarian about heartworm before you leave. Your veterinarian will identify heartworm risk areas and prescribe appropriate preventive medication, if needed.


Can my cat get heartworm?

Although dogs are the natural hosts for heartworm, cats will occasionally become infested as well. Preventive medication is therefore recommended for cats traveling to high-risk areas during the mosquito season. Heartworm tests and medications specifically for cats have recently become available - talk to your veterinarian.