Protect Your Pets from Dangerous Mosquito Bites & Heartworm

Posted by Mosquito Squad

May 2, 2013

Years ago, we took our dog to the vet for a normal checkup. As we waited to see the vet, I noticed one of those small scientific models depicting heartworm disease, which is transmitted by mosquitoes. If you’ve never seen one, it shows these long worms intertwined throughout the heart, and it’s very disturbing. It stuck with me and to this day, we are very diligent about heartworm prevention with our two dogs. I have invited Dr. Sara Gilbert, a veterinarian with Millis Animal Hospital to share her thoughts about heartworm and steps for prevention.

Most of us with pets in Missouri have heard about heartworm disease but now that spring is here it’s time to revisit this topic to help protect the health of our furry companions.  Heartworm is a parasitic disease of mammals seen commonly throughout our area.  Although heartworms can infect a wide range of animals, this article will focus on dogs and cats.  Both dogs AND cats can get heartworm disease.  These worms live in the heart and blood vessels and cause serious and potentially lethal health problems for family pets.  The parasite is spread when a mosquito bites an animal with heartworm disease then later bites another animal.  The baby worms, called microfilaria, NEED the mosquito to grow into adult worms and be spread to the next host.

Dogs and cats with heartworm disease may not show any outward signs of the disease for a long time, but eventually, they are likely to become very sick if they have adult worms living in their heart and bloodstream.  These worms clog up the vessels and can get lodged in areas important for blood flow.  The most common troubles in dogs are related to breathing and exercise problems that are similar to heart failure.  Although cats are less susceptible to heartworm, fewer grown-up worms can cause more dramatic and variable kinds of symptoms for them.  The good news is that heartworm disease is extremely uncommon in pets that take preventative medication for heartworm disease.  While there is a treatment for some pets once they are positive for heartworms, it is currently quite costly and can be stressful to the pet and owners.

The first step in getting your pet on preventative medication for heartworm is going to see your veterinarian. Usually, a blood test must be performed to ensure that the preventative medication will be safe for your pet.  It may be dangerous to give a pet that has heartworm disease the preventative, depending on how long the worms have been in their system.  If your pet is negative for heartworm, then a monthly medication may be given that kills the baby worms transmitted by mosquitoes before they can grow into the problematic adults.

Because winters have been milder the past few years and the mosquito breeding season longer, you should ideally give the medication on the same day each month to be sure your pets are safe.  If your pet misses a dose you will need to retest them later in the year to make sure they are still negative.  Please be honest with your veterinarian if you have missed, skipped doses frequently and the vet will take steps to make sure your pet is less likely to have problems in the future.  Unfortunately, all it takes is one infected bite to put your pet at risk.  Controlling the mosquito population in your yard will also lower the risk of transmission as well.  Living in areas with an abundance of water and mosquitoes increases your pet's chances of being exposed.  It is not recommended that you mist mosquito deterrent on your pet directly.

Talk to your veterinarian about any additional questions you may have. There are many options for prevention available.  Prevention is much less costly and easier on your pet than treatment once they have the disease.  For more information, you can also go to the Heartworm Society’s website at to get the most reliable and current information.

Dr. Gilbert graduated with honors from Colorado State University School of Veterinary Medicine and Biomedical Science in 2006. She primarily focuses on canine and feline medicine at Millis Animal Hospital in St. Louis, Missouri.