Heartworm is a serious and often fatal disease affecting mainly dogs, although cats can also be infected.

Dogs and cats of any age are susceptible, which is why prevention is important. Without proper prevention, pets are at risk of contracting this potentially deadly disease.

Heartworm disease has been found in many parts of Canada, with southern and southwestern Ontario reporting the most cases.

Heartworm is spread when mosquitoes infected with the disease bite a dog or other susceptible animal, causing infective larvae to enter through the bite wound. In six months time the infective larvae mature into adult worms. These worms live in the right side of the heart and arteries or lungs, causing extensive damage and sometimes death.

Many dogs abandoned in Louisiana following Hurricane Katrina became infected with heartworm disease. As many of these dogs were placed in new homes across North America, we are seeing increased numbers of cases in Ontario and elsewhere.

Heartworm prevention is safe, easy to manage and inexpensive compared to treating a pet for heartworm disease. There are a variety of preventative products available, including monthly chewable tablets, and monthly topical applications that are absorbed through the skin. Many of these products also control intestinal parasites, fleas and other external parasites, depending on the drug used. These medications interrupt heartworm development before adult worms can reach the heart or lungs.

We recommend that all dogs be tested periodically for heartworm disease, and to start a heartworm preventive medication by the first of June every year.