What month should a dog start taking flea & tick and heartworm medications in Toronto?

Hi Michelle,

Thanks for your question.

It’s important to point out that this question should be answered by the prescribing veterinarian. I would never give direction on the initiation, dosage, frequency or use of any prescription medication. Only your veterinarian can do that.

I can, however, discuss the seasonality of these diseases in Toronto.

Heartworm season typically runs from June 1st to October 10th. Be aware that it can lengthen or shorten depending on the type of weather we experience during that particular year. The heartworm larvae need a certain number of days in a row of persistently elevated temperatures in order to mature with the mosquito’s body. This is the reason that these dates are quoted for Toronto. For anyone living elsewhere, you’ll need to check with your veterinarian about the season and risk of heartworm disease in your area. Some veterinarians will recommend using heartworm medication year round or start it earlier as it often protects against fleas as well which can occur outside of the heartworm season.

Ticks are more difficult. In areas of Ontario, they have now become endemic, meaning they can be present year-round. They weren’t often found on dogs in the very hot and very cold months of the year, but this has dramatically changed. We will now see ticks on dogs in months like December, January, July and August. Again, I would recommend you speak with your veterinarian, but it can now be considered a year-round problem. However, the risk dramatically increases through the summer based on the lifestyle of pets, the activity of the ticks, and access to tick-infested areas.

I hope this helps.

Dr. Clayton Greenway