Heartworm in Southern Ontario

So why even think about heartworm when we live in Ontario? It’s a “southern” disease, right? Wrong. While the incidence of heartworm in Ontario is low, especially compared to the southern United States, it still exists. In fact the highest incidence of disease in Canada is in Ontario. In 2018 there were 150 positive tests, and those are just the dogs that were tested. With more dogs coming up from heartworm endemic areas through rescue groups and the untreated foxes and coyotes it is likely we will see more. Given the serious nature of the disease, we do recommend preventative measures for your dog.

How is Heartworm Transmitted?

Heartworm is a blood-borne disease caused by Dirofilaria immitis, an approximately 8 inch long spaghetti-like worm; during warmer months it is spread by mosquitoes.

A mosquito bites an infected dog, fox or coyote and takes in the larval stage that is circulating in the blood. Later, the mosquito can bite your dog and inject the larva (immature heartworm) into your dog’s bloodstream.

Over the next 6-7 months it develops into an adult worm, living in the main blood vessels of the heart. Here it can lead to potentially life-threatening heart disease.

Symptoms of Heartworm

• Cough
• Lethargy (tiredness)
• Exercise intolerance
• Abnormal fluid accumulation in the pet’s abdomen or chest, often due to congestive heart failure
• Some dogs may be asymptomatic and show none of these signs

Diagnosing Heartworm

Unfortunately we cannot rely on the absence of clinical signs to say your dog is free of heartworm. Fortunately heartworm disease can be diagnosed through a simple blood test. This test detects the antigen of the adult worms. If positive, a second confirmatory test will be performed prior to initiating treatment. We recommend testing your dog every other year unless there is a history of travel to higher risk, endemic areas or any preventative medication was missed. Please speak with our staff to find out if your dog is due for a heartworm test.

Prevention is Key!

For those dogs in the Oakville area, heartworm “season” is typically June to November. It is during this time that it is important to have your dog on an appropriate monthly preventative. This preventative kills the larval stage before it can develop into adult worms and before they can cause damage to your dog’s heart and lungs. There are several safe products available that effectively prevent heartworm disease; some are given orally and others are applied topically. For information on which product is right for your dog please contact us.