Why Stop Mosquitoes from Biting Your Dog?

Do you like getting bit by mosquitoes?  I don’t.  Mosquitoes love me. Always have. Mosquitoes are not only a nuisance but they transmit disease to us and our pets.  Over one-million deaths (in human) a year are attributed to mosquitoes worldwide. Most concerning to pet parents is heartworm disease. So why shouldn’t we stop mosquitoes from biting your dog?

I went back into private practice full-time last summer after a 15 year hiatus. I was surprised at the popularity of flea and tick preventatives which force the insect to bite your pet before they could die.  It seems very counter intuitive to me.  More on that later.

Heartworm infection is common in dogs throughout the United States (cats get them too).  They have the ability to do a lot of damage and can be fatal.  Luckily, it is preventable.  Even with the advent of great preventatives there has been a steady increase of heartworm positive dogs in the past 10 years.

The Katrina Effect

Do you remember the heartbreaking images of pets who were left behind during Hurricane Katrina?  The increase of heartworm disease that followed these newly adopted pets is called the Katrina Effect.  Areas of the United States that had little to no heartworm disease in the past now were seeing positive cases.

This occurs because of transplanted dogs who were Heartworm positive from endemic areas (like the Mississippi delta) to their new homes.  They became a reservoir in their new neighborhoods.  Transplanting these pets to areas where they could be adopted was absolutely the right thing to do.  As pet owners, we just need to be aware of the realities of the Katrina Effect.  No matter where you live, there is a chance your dog can become infected with Heartworm disease.

Heartworm in My Home

Heartworm positive dog
Biggie Molls after her second heartworm treatment.

In 2018 we fostered a puppy mill dog who was surrendered to Angels Left Behind Rescue.  She is a Pug named Molly (we call her Biggie Molls) and came to the rescue after breeding non-stop for  nearly 10 years.  She was relinquished because she was heartworm positive. Molly lived with us through her treatment.  As a veterinary nurse I knew it is not easy but didn’t realize how emotional it would be for me, maybe because I know too much.

During treatment, we are poisoning the parasites and killing them off.  Protocols vary but Molly went through three injections. The time frame, start to finish for treatment can last about three months.  It is crucial to keep a dog quiet post treatment. Cage rest and only leashed walks to eliminate in the back yard and return inside.  Luckily Molly is a quiet, always ready to take a nap kind of dog.  High energy dogs can find this restricted activity challenging.

Year-Round Prevention is Best

Most veterinarians, supported by the American Heartworm Society, CAPC, recommend year-round prevention.

Mosquitoes can survive in standing water, heated garages, or sheds during the winter.   With the fluctuation of temperatures, it’s possible to have mosquitoes in typical cold weather months.

“Deworming” monthly is a key feature of many heartworm preventatives.  Intestinal worms are a bit hardier than mosquitos.   They can be acquired through exposure to animal feces even after a freeze.  Don’t forget those who travel with their pets to warmer weather from colder northern climates.  Pets coming back and forth serve as reservoirs for mosquitos to pass on the disease.

Monthly preventatives are easily given at home through tablets, chewables, or topicals.  They work by eliminating the infant stages of the heartworm passed from the mosquito and have slightly different claims against other external and internal parasites.  Pet parents can add to monthly heartworm preventatives and protect their pets from bite of fleas, ticks and mosquitoes.

Repellency Matters

Mosquitoes are the vectors which transmit heartworm disease.

The American Heartworm Society (AHS) recommends in addition to a (year-round) heartworm preventative, apply an EPA registered mosquito repellent to your dog.  This is genius!  Why you ask?

For years we had a heartworm prevention product that was daily.  Then 20 some years ago came the dawn of the monthly preventatives.  These are fantastic for many reasons. The way these preventatives work allows your pet the chance to become infected with heartworms every month, then clear the infection with the monthly dosing.  Still a huge improvement.

But in addition to clearing that new infection every month, why not try to stop your dog from being bitten from the mosquito in the first place?

I’ve been in veterinary medicine for almost 20 years.   In 2019 I watched a continuing education webinar by two veterinarians that discussed the clinical importance of stopping that cycle.  Stop the vector (mosquito) from biting and spreading the disease. This is the first time I had learned, from the technical side, why repellency matters.

My pack of three are protected from not only ticks and fleas but mosquitoes that may carry heartworm disease.   I apply Vectra 3D, a topical that works outside of the body where you want to stop fleas, ticks and mosquitoes.  They also get a monthly heartworm preventative – that’s internal to kill the internal parasites.

Top Tips for Heartworm Prevention

The best thing we can do as dog parents is to follow the AHS and CAPC guidelines when it comes to heartworm and flea/tick/mosquito prevention:

  • Give your dog an FDA approved monthly heartworm prevention product
  • Give your dog a topical EPA approved flea/tick/mosquito repellent
  • Annual Heartworm testing
  • Support your local veterinarian, ask for a generic heartworm prevention from their pharmacy


The evolution of heartworm prevention to me is similar to the Maya Angelou’s famous quote, “Do the best you can until you know better.  Then when you know better, do better.”  We’ve gone from daily’s to monthly’s that hit on the inside where internal parasites live.  Now we can add an external prevention that repels and acts on the parasites that live outside of the body.  This allows us to do better for our dogs

Happy Pet Parenting,

Leslie the Pet Nurse

Vectra 3D CANNOT be used on Cats


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