Busting Three Heartworm Myths

By: Nancy Turner, DVM

TVMA Member
Dallas, TX

Published April 2015

I have often found myself sucked into an episode of MythBusters on the Discovery Channel, hanging onto every experiment, hypothesis and outcome. The last show I saw was one where the group tested some common deterrents for driving away certain animals, and it got me thinking. Almost every day I am asked to debunk animal-related myths, and while many of these common myths are harmless, some can be downright dangerous to your pet. The myths surrounding heartworm disease are ones I consider to have great potential for harm, mainly because of the serious effects that heartworms can have on dogs and cats. That is why I am “busting” the three most common heartworm myths.

Myth #1: My pet spends the majority of his time indoors so he doesn’t need heartworm prevention.

False: While the outdoor dog or cat is more likely to be bitten by infected mosquitoes, mosquitoes do come inside looking for a blood meal and will feed on cats and dogs. Multiple scientific studies have found a significant number of heartworm infections in cats living exclusively indoors (American Heartworm Society). It only takes one mosquito bite to inject the larval stage of the heartworm into your pet, and I know that I have been bitten by a mosquito while I was inside. Surely my dog and cat have as well!

Myth #2: Mosquitoes are only active in the spring and summer, so I don’t have to give heartworm prevention year-round.

False: My friends, this is Texas, and if this winter was any indication, you never know what is going to happen. What is that old saying? “Don’t like the weather in Texas? Wait 5 minutes!” Some are under the impression that a hard freeze, or even multiple days of freezing weather, will kill mosquitoes. Well, it may kill the adult mosquitoes, but the eggs are pretty sturdy little buggers and can lay dormant for up to two years. They are just waiting for a hint of moisture or a slightly warmer day to hatch and start the process to becoming those pesky flying adults. Also, mosquitoes are smart and will try to migrate into a warmer spot (i.e., inside our homes) when the weather changes to continue feeding (American Heartworm Society). All in all, there is no way to predict where or when they will show up, and that is why we recommend prevention year-round.

Myth #3: Cats can’t get heartworm disease.

False: While it is true that heartworm disease in cats is less common than in their canine counterparts, this does not mean that they are not affected by the parasite. Cats do seem to be more resistant to adult heartworm infection than dogs, but this only means that the larval or juvenile stages have a much harder time becoming adults and the juvenile stages can still cause a significant amount of damage on their own. The signs of heartworm infections in cats are generally related to these roaming larval stages (American Heartworm Society). Geographic prevalence of feline heartworm infection (adult worms) generally follows canine infections, but adult infection occurs at approximately 10 percent of the prevalence rate for dogs (CAPC). North Texas has one of the highest incidents of canine heartworm infection in the country, so it is something that we, as veterinarians, think about when a cat is ill. Signs of heartworm infection in cats include coughing, breathing difficulties, chronic vomiting, lethargy and sudden death. That is why we strongly recommend year-round heartworm prevention in all of our feline patients.

I really hope this myth-busting helped explain some common misconceptions about heartworm disease and prevention. Veterinarians have multiple heartworm prevention options available and would love to help pick the best one for your pet.

Nancy Turner, DVM, is a graduate of Texas A&M College of Veterinary Medicine who lives in Dallas, Texas. Dr. Turner practices at CityVet White Rock.