The short answer
Yes. Ontario has confirmed heartworm cases, and Oakville sits in the province’s highest-risk zone. Prevention is far less costly than treatment, and the recovery from heartworm infection is rough on your dog. This one is not worth skipping.
Ontario’s heartworm risk
About 0.5% of dogs in Ontario test positive for heartworm. That sounds low, and it is low compared to the southern United States. But that number only stays low because most dogs are on prevention. If coverage drops, the infection rate climbs.
The risk is not evenly spread across the province. Roughly 80% of Ontario’s heartworm cases occur south of the 403/402/401 highway corridor, between Sarnia and Hamilton. Oakville and the rest of Halton Region are right in that band. The combination of proximity to Lake Ontario, green space, and summer humidity makes for solid mosquito habitat.
Heartworm season in southern Ontario runs from approximately June 1 through November 1, matching the period when mosquitoes are active and temperatures stay above 14 degrees Celsius long enough for the heartworm larvae to develop inside the mosquito.
Prevention vs treatment
Monthly heartworm prevention is inexpensive, and many products do double or triple duty — covering ticks, fleas, and intestinal parasites alongside heartworm. The right product depends on your dog’s lifestyle and risk factors, so it’s worth talking to your vet about what each preventive is actually designed to cover before comparing options.
Treatment, by contrast, involves a series of injections, strict exercise restriction for months, and a significant cost. Some dogs need two rounds of treatment. And even after successful treatment, permanent heart and lung damage can remain.
Years of prevention cost a fraction of one round of treatment.
What about year-round prevention?
The Canadian Parasitology Expert Panel recommends prevention from June 1 to November 1 in Ontario. Some vets now recommend year-round prevention, partly because climate change is making mosquito seasons less predictable, and partly because several prevention products also cover ticks and intestinal parasites.
Your vet can recommend the right approach based on your dog’s lifestyle and risk factors.
Key takeaways
- Oakville is in Ontario’s highest-risk zone for heartworm, south of the 403/402/401 corridor.
- About 0.5% of Ontario dogs test positive. That rate stays low because of widespread prevention.
- Prevention is far less costly than treatment, and many products also cover ticks, fleas, and intestinal parasites.
- Heartworm season is June through November in southern Ontario.
- Year-round prevention is gaining favour, especially with combo products that also cover ticks and parasites.
- Talk to your vet about what each preventive is designed to cover before comparing options.
References
- Canadian Parasitology Expert Panel. “Ontario Parasite Data.” usask.ca
- Toronto Humane Society. “Heartworm Testing and Prevention Information.” torontohumanesociety.com
- Ontario SPCA. “Commonly Asked Questions About Heartworm in Dogs.” ontariospca.ca
- Vetster. “The Cost of Heartworm Prevention vs. Treatment in Dogs.” vetster.com