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Advice from Dr. Chris: Can I Stop Using a Flea/Tick or Heartworm Preventative in Winter?

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Authored By: Chris Vanderhoof DVM, MPH

It’s late February and for many in the US, it’s the peak of some pretty frigid temperatures with winter storms bringing plenty of snow and ice. For many it is also the time to take a break from reminders to give their dogs preventative products against fleas, ticks, and heartworms.

After all, it certainly seems less likely to see these bugs around, especially when there’s a thick layer of snow on the ground and nature seems to be at a standstill.

Some research seems to confirm this view. According to a study published in Parasites and Vectors in 2017, of over 500 pup parents, the average owner responded that their pets needed about 10 months of prevention. But even so, based on product purchases, the average pet coverage was actually only 6 months. 

It also makes sense that folks living in warmer regions would recognize the need to use preventatives more regularly while folks in colder regions would see less need at certain times of the year, believing these creepy crawlies are dead like most everything else for at least a couple of months.

And study findings confirm this view too. While opinions varied, the folks responding from the Northeast believed their dogs needed less prevention compared to other regions.

But do these critters really die during the winter like many believe? If they come back to plague our pups year after year, where do they actually go when it gets colder? Is there such a thing as a flea and tick season, especially in colder climates?

In 2019, a video went viral that was posted by the staff of a local veterinary hospital in Boston, New Hampshire in early January, of a dog who got into an unfortunate altercation with a porcupine. While sedated to have the quills removed and wounds cared for, a fully engorged tick was found embedded in the dog’s skin. This occurred with several inches of snow on the ground. 

Why did the video go viral? People were shocked. In one of the coldest states in the US, well-known as a winter sports destination, in the middle of winter, a dog actually had an embedded tick.

It would seem that ticks don’t really die just because it gets cold or because there’s snow on the ground.

In fact, as staff of the vet hospital in New Hampshire attested to in interviews, some ticks remain dormant (but not dead) while others stay active. Ticks can overwinter very well beneath a layer of snow, hanging around the walking paths that dogs and their owners trample out. 

While a misperception of the seasonal activity of ticks is more understandable in the coldest northeast, this idea of a defined “tick season” stretches very far south even to at least my region of Virginia where winters are certainly milder than in New Hampshire, but we still get at least a couple of snow and ice storms a year.

I find not infrequently that folks believe ticks and other bugs are largely gone after the first official frost that occurs in late fall. But if ticks survive well in a US state that stays pretty well snow-covered for at least 4-5 months of the year, one single frost in a milder climate region is very unlikely to do much to them.

My own mother, an avid gardener, attended a Master Gardener’s conference here in Virginia a couple of years ago. Included in the conference was a great deal of information about ticks, with gardeners naturally being at higher risk of exposure.

To illustrate just how resilient ticks are, one of the speakers had frozen a tick in a small block of ice. While he lectured, he allowed the block of ice to thaw on camera. By the end of his lecture, the block of ice had melted and the tick was crawling around.

In Virginia, we see changes in temperature and weather all throughout the winter. As I write this, it was a brisk 22 degrees just two days ago. This morning? It was a balmy 60 degrees. It’ll probably stay warm for about 1-2 more days before it gets below freezing again.

If your region sees such fluctuations even for just a couple of days, be aware that ticks may very well be out and about. I’ve suspected that many dogs showing positive test results for tick borne disease were exposed during these periods or during late fall or early spring when the persistence of ticks is underestimated.

Also, don’t forget that even a short weekend trip traveling to a warmer region carries just as much potential risk as a 2 day warm-spell in your own colder region.

What about fleas? 

While ticks can survive outdoors pretty well as we’ve just learned, fleas don’t do so well in the cold. 

But just like ticks, they manage to survive year to year somehow. So how do they do it?

Fleas survive by overwintering in the warmest locations they can find. They often continue to feed on small animals, like rats and mice, that burrow during the winter. But because these small animals often burrow in and near homes to benefit from the nearby warmth themselves, fleas can still be found in close proximity to pets.

Sometimes, we see an uptick (no pun intended there) in flea infestations in winter. Fleas will also find opportunities to hitch rides on dogs and cats venturing outdoors so that they can make it indoors where it’s warmer. With one female flea being able to lay up to 50 eggs per day, only one or two fleas can turn into hundreds in only a couple of weeks. 

Flea eggs that have already been laid may also remain dormant, just waiting for the right temperature and humidity to hatch. Even a couple of days of warmer weather could see fleas return during winter, even if it’s for just a brief period.

Mosquitoes, the vectors of heartworms that cause deadly heartworm disease in dogs (and cats as well), are a little more predictable but no less resilient.

Mosquitoes become far less active at temperatures below 50 degrees. While some species of mosquitoes may be killed by frosts and freezing temperatures, others will simply go into a dormant state, hibernating until the climate becomes more favorable again. 

Still others that may die during the winter ensure their offspring survive by making sure eggs are laid before temperatures really drop. The eggs themselves persist throughout the winter, waiting for it to get consistently above 50 degrees or more for a few days to hatch. 

The last consideration to continue preventative care for your pup throughout winter is the intestinal parasite prevention coverage that many heartworm prevention products also provide.

While there is a wide variety of intestinal parasites that different products out there may protect against, there are quite a few in general whose eggs or cysts persist very well for months or even years in the soil. 

Many intestinal parasites don’t require environmental conditions to be more favorable to become infective. They simply need to be ingested. This could happen as easily as getting licked off a dog’s foot during some self-grooming. The internal environment of a dog’s body triggers eggs to hatch and the parasites to emerge. This risk can be present year-round regardless of what the weather is doing. 

There are lots of different prevention products out there that target different combinations of parasites. What products folks choose for their pets may depend on what a pup is most at risk for in a particular region, as well as personal preferences. The best prevention product for a particular dog is a discussion best kept between a pet parent and their veterinarian.

But hopefully, regardless of what products you choose, you’ll see the importance of choosing something, and continuing its use year-round, even in regions traditionally considered to have distinct seasons. 

After all, fleas, ticks, mosquitoes, and intestinal parasites have all survived for millions of years, including a couple of mass extinctions and the last ice age. A little seasonal cold with some snow and ice, in the grand scheme of things, isn’t too much of a problem for them. 


Dr. Chris is considered one of the country’s leading veterinarians. He completed a dual Doctor of Veterinary Medicine degree and Masters in Public Health at Virginia Tech, a top veterinary school in the country.