How Do Dogs Get Heartworm?

Stephanie Dube Dwilson

You want to keep your dog as healthy as possible, and that means protecting your pup from the danger of heartworms. But how do dogs get heartworm disease? Summer is here, and the warmer months could put your dog at a higher risk because heartworms are transmitted by mosquitoes.

Dogs Get Heartworms from Mosquito Bites

Heartworms, also known as Dirofilaria immitis, are spread through mosquito bites.1 Dogs are known as "definitive hosts" because heartworms can grow and reproduce in them. After an infected mosquito bites a dog, the larvae develop into adult heartworms in about six to seven months.2 They live in the dog's heart, mate, and produce offspring called microfilariae that live in the dog's blood vessels. When a mosquito bites a dog, that mosquito may pick up some of the microfilariae and pass it on to other dogs.

Heartworms can live five to seven years in a dog. Although the average number of worms in an infected dog is 15, it can range from one worm up to 250.If you suspect your dog may have heartworms, you should see a veterinarian for treatment immediately.

It's worth noting that cats can get heartworms too. Cats are an atypical host and worms have a tougher time surviving, but it's not impossible. Because heartworm treatment for dogs can't be used to treat cats, veterinarians typically recommend using medication to prevent cats from getting heartworms.4

How to Protect Your Dog

Even though mosquitoes tend to increase during the warmer months, experts recommend using a preventive year-round to protect your dog.Quite a few over-the-counter products designed for fleas and ticks can also protect against mosquitoes. Adams Plus Flea and Tick Prevention Spot On for Dogs kills and repels mosquitoes. It also protects against fleas and ticks for up to 30 days.

Adams Flea & Tick Collar for Dogs and Puppies repels mosquitoes* for up to six months. Each tin comes with two collars for up to 12 months of mosquito* repellent (flea, tick, and mosquito* control). The adjustable and water-resistant collars use extended-release technology to provide lasting protection.

Remember, dogs can't directly pass heartworms to other dogs. Heartworms are only passed on when a mosquito bites an infected animal and then bites another dog that isn't infected.

How to Protect Your Yard and Home

While protecting your dog from mosquitoes, it's a good idea to protect your yard and home too. Adams Plus Flea & Tick Indoor Fogger kills mosquitoes and many other insects, including silverfish, adult fleas, hatching flea eggs, flea larvae, cockroaches, ants, spiders, and ticks. You can further protect your home by fixing broken windows, screens, and other gaps that mosquitoes might use to sneak inside.

For the outdoors, try Adams Yard & Garden Spray. This spray kills fleas, ticks, mosquitoes, and ants. You can further cut down on mosquitoes in your yard by removing standing water where they breed. You might also want to avoid walking your dog at dusk and dawn when mosquitoes are most active.

The summer months certainly bring more opportunities to spend time outdoors, but they also bring more chances for your dog to catch heartworms. The good news is that it only takes a few preventive steps to keep your pup mosquito-free.

1. FDA. "Keep the Worms Out of Your Pet's Heart! The Facts about Heartworm Disease.",

2. FDA. "Heartworm Lifecycle.",

3. FDA. "Keep the Worms Out of Your Pet's Heart! The Facts about Heartworm Disease."

4. American Heartworm Society. "Heartworm Basics.",

5. Eckstein, Sandy. "Heartworms in Dogs: Facts and Myths.", 23 April 2018,

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