Do Pets Need Year-Round Heartworm Protection?


Mosquito bitephoto 2008 dr_relling | more info (via: Wylio)
A reader asked a good question in the comments of a recent post.

Dr. Barchas, do you recommend heartworm prevention year round? Right now I only have my cats on the meds from early spring to late fall. That’s the time I leash walk them and I’m in the DC area where mosquitoes are a problem. Is there any danger to skipping the meds during the winter when the cats are indoors all the time?

I recommend year-round heartworm prevention in all pets. So does the Companion Animal Parasite Council (a group of experts dedicated to preventing parasitic infestations in pets).

Heartworm is spread by mosquitoes. Mosquitoes aren’t common when the mercury drops below freezing. The heartworm parasite thrives best in warm, humid environments. Winter interferes with its life cycle. It therefore has been common for veterinarians in places such as Washington, DC or Chicago, where it’s hot in the summer and freezing in the winter, to recommend heartworm prevention only during the warmer months.

And, to top it off, mosquitoes are more common outdoors than indoors. Therefore, one might reasonably wonder whether an indoor cat needs heartworm prevention during the winter.

Here’s the rub. There are ubiquitous species of mosquito that can live their entire lives indoors in basements, crawl spaces, and air ducts. These mosquitoes can feed on pets and spread heartworm year-round indoors in any climate. Wintertime transmission of heartworm to indoor cats is rare, but not impossible.

The most commonly used heartworm preventatives are incredibly safe, and most of them eliminate or prevent other parasites as well. It is my opinion that year-round heartworm prevention is in pets’ best interest.

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