Heartworm Myths Busted

By: Sarah Wooten, DVM, CVJUpdated:

Heartworm Myths Busted

Heartworm Myths and How to Protect Your Pets

All pet parents want their pets to be free of internal parasites, but there are so many opinions and heartworm myths on the Internet that it can be downright impossible to know what’s best for their pet.

When it comes to heartworm disease, you want to make sure that the information you are basing your decisions on is thoroughly vetted. In the interest of protecting you and your pet from internal parasites, here’s a list of the most common heartworm myths, heartworm risks, and heartworm testing and prevention methods. Take these into consideration so you can be armed with the heartworm facts you need to make the best healthcare decisions for your pet.

Know Heartworm Facts vs. Myths

(1) I don’t need to give pet prescription heartworm medicine because we don’t have heartworms in our area. While it is true that the risk of heartworm disease is higher in some places than others, if you live anywhere in the United States, your pet is at risk. The historical belief that some areas are heartworm-free can no longer be trusted, especially with widespread interstate movement of animals spreading the disease and causing local pandemics. After Hurricane Katrina, dogs were rescued from New Orleans and trucked to foster homes all over the country, taking heartworm disease with them into areas that had not been previously exposed. All it takes is one dog with heartworm disease to put all other dogs and cats in the neighborhood, or at the dog park, veterinary hospital, groomer and boarding facility at risk.
While you can’t know the heartworm status of every dog in your community, you can protect your own dog or cat with heartworm prevention. To get a better idea of recent heartworm testing results in your area, visit the CAPC parasite prevalence map.

(2) My pet lives indoors, so she’s not at risk. If I’ve heard this once, I’ve heard it a thousand times—It’s the most common of the heartworm myths mistaken for heartworm facts, and it makes me face-palm every time.
Yes, heartworms in dogs can only be passed by mosquitoes, and yes, mosquitoes live outside. However, you are fooling yourself if you think mosquitoes can never get inside your house and infect your pet with heartworm disease. Just the other day, I swatted a mosquito in the room that is furthest from any door in my house, and it was a chilly Colorado day in October!
If your dog ever goes outside to urinate or defecate, or if your cat sits on a patio, or basically if you have doors in your home, then your dog or cat is at risk, and needs to be protected against heartworm disease.

(3) You only need to give heartworm prevention in the summer. Mosquitoes can be active even when it is cold outside. In some areas, like Texas, the Deep South, New Mexico, Arizona, Florida and California, mosquitoes are active year-round, spreading disease like wildfire.

Heartworm prevention not only protects your pet from heartworm disease, but it also protects your pet from other internal parasites, such as hookworms and roundworms, which can be transmitted to people—particularly children. A hookworm or roundworm infestation can occur year-round. I recommend keeping your pets on year-round internal parasite control in the form of heartworm prevention to protect your human and fur family.

(4) I keep my pet on heartworm treatment year-round, so she doesn’t need a yearly heartworm test. This is another one of the most common heartworm myths I get from clients. If you don’t know why we are testing, then it makes sense to ask. In fact, I encourage my clients to ask! The reason why we test pets for heartworm disease before dispensing the medication is because no medication is 100% effective, and there has been some incidences of heartworm populations that are resistant to medication in the southern states. We test pets to make sure the medication is effective and administered properly, and to get an idea of the heartworm status of the dog population in a given area.

Some heartworm tests have the added benefit of testing for tick-borne diseases, such as Lyme and Anaplasmosis. This is important information, because if a dog comes up positive for exposure to ticks that carry Lyme, then there is a high likelihood that humans have been exposed as well (dogs tend to go where their people go). The heartworm testing provides veterinarians with critical information needed to not only protect canine and feline populations, but human health as well.
Some veterinary offices will only require testing every other year if the client is consistent about giving heartworm medication every month. If you consistently keep your pet on heartworm prevention, ask your veterinarian about testing every other year, unless you live in an area that’s at risk for resistant heartworms.

(5) Cats don’t get heartworm disease. False! Cats can get heartworm disease just like dogs. Worse, cats are more likely to have a cardiac event with heartworm disease because their hearts are so small. It is a problem of volume—if a large dog has one heartworm living in his right atrium, then you may not notice any heartworm symptoms. If a cat has a single heartworm, it is a much bigger problem, because there is no room in the chambers of a small feline heart for a foot-long worm. Cats are not a normal host for heartworms, and heartworms in cats often don’t survive long enough to become adults, however, even immature or dead worms can cause real cardiac or respiratory problems in cats in the form of a disease called heartworm-associated respiratory disease. If the worms die, they can cause irreversible inflammatory damage to the heart and lungs, predisposing the cat to asthma. The other challenge with cats is that we have no good way to treat them once they are infected, making prevention the only way to protect a cat from developing often fatal heartworm disease.


By: Sarah Wooten, DVM, CVJUpdated: