Let’s Talk About Those Pesky Heartworms

Hey, Northern Hemisphere pet parents! Have you been keeping an eye on the weather lately? Even in sunny Tampa Bay, we’re experiencing some cool nights following Hurricane Milton. It’s not every night, but even just one cool night a month can signal the end of heartworm season.

You may have noticed I didn’t mention mosquitoes.

While daytime temperatures are still creeping into the 70s and 80s—just yesterday, I had a consultation with someone in Manhattan where it was 80°—the low forecast tonight is 45°. That’s a sure sign: heartworm season is officially done!

Now, I know the pharmaceutical companies might not be thrilled to hear this, because neither your veterinarian nor the drug companies are making money if you’re not giving heartworm prevention in the winter. This is likely why many drug companies have started combining heartworm prevention with flea and tick medications—because those pesky critters are a year-round concern.

So, what exactly are heartworms? They’re parasites transmitted through mosquito bites. For a mosquito to pass on heartworms, it first needs to bite a dog that’s already infected. The baby heart worms then spend some time in the mosquito’s gut before they can be transmitted to another dog. That’s a lot of steps that must be taken for your dog to contract heart disease.

Plus, each of you reading this has a pampered house dog, I’m sure. If you didn’t, you probably wouldn’t be here! Your dogs are loved and cared for, not tied up outside in a swamp.

But here’s the key detail: when overnight low temperatures drop below 58°F, those baby heartworms can no longer survive in the mosquito. So, if there’s even one night each month where the low falls below 58°, heartworm season is over!

So, what’s next? If you draw a line around the globe at the level of Tampa Bay, anything north of that line is officially out of heartworm season.

When does heartworm season start again? Keep an eye on the weather! Springtime will kick off the new season as temperatures warm up. Mark your calendar for the last night the temperature drops below 58°. Heartworm season will begin 30 days after that date.

For instance, in Tampa Bay in 2024, that last chilly night was April 1. In Indianapolis, it was June 10.

So, keep watching the weather and stay proactive about your furry friends’ health!