As a responsible pet parent, you’ve definitely heard of heart disease, and know it’s important to protect your pets, but you may feel confused by all the contradictory information out there. Here’s some of the most common myths about heartworm and the truth about these prevailing misconceptions.

1. You don’t need to give heartworm prevention in the winter.
Mosquitoes hibernate in the winter and can come out any time it’s over 50 degrees Fahrenheit, even if it’s just a single, unseasonably warm day in the middle of winter. Since heartworm prevention works by eliminating any larvae your pet may have picked up in the previous month, you’ll need to keep your pet protected even when you don’t expect any warm days in the near future. By giving your pets heartworm preventatives year-round, you won’t risk leaving them unprotected. Most preventatives also protect against other internal parasites like whipworm and roundworm, which have been shown in studies to peak in the wintertime.

2. Indoor cats don’t need heartworm protection.
Mosquitoes that carry heartworm can easily infect indoor cats by entering your home. Heartworm affects cats and dogs differently, but it can be fatal to either species. In cats, heartworm larvae do not tend to mature into adults, and the parasitic load tends to be relatively low compared to dogs. However, this isn’t necessarily good news. The symptoms are subtle, nonspecific, and tend to develop gradually. Coughing, fatigue, and lack of appetite are the most common, but some cats collapse or even die suddenly before they are ever diagnosed. Diagnosis is more complicated in cats, as only adult heartworms are detected in the typical blood screen. Unfortunately, there is no safe, approved treatment for heartworm in cats. It can be managed, but not cured. On the bright side, you can protect your cat with a chewable or spot-on heartworm preventative.

3. Heartworm is contagious.
Thankfully, this isn’t true. Cats and dogs only get heartworm when bitten by an infected mosquito. So, if you ever have a heartworm-positive animal in your care, you will not need to worry about them passing it to your other pets. As long as your other pets take a preventative, they will be safe. While humans can, in rare cases, contract heartworm disease, we cannot get it from our pets.

4. Herding breeds like sheepdogs and collies can’t take heartworm medication.
It is true that certain breeds of dog, including Australian shepherds, sheepdogs, collies, border collies, and other herding breeds are more likely than other dogs to have a genetic mutation that causes a sensitivity to certain drugs. Dogs with the MDR1 mutation can have adverse reactions to ivermectin, the active ingredient in some heartworm preventatives. However, it’s rare for dogs to have an adverse reaction even if they have the MDR1 mutation. Recorded cases of adverse reactions involved doses many times higher than that used in heartworm medication, either because it was given improperly, or because the dog got into ivermectin paste made for horses or cattle. You can have your dog tested for the MDR1 mutation, and you also have the option of using Interceptor, a heartworm preventative that does not contain ivermectin.

5. Heartworms show up in poop like other parasites.
Just because you cannot see worms in your cat or dog’s poop does not mean that they are parasite-free. You can sometimes see segments of tapeworms or long, stringy roundworms in feces, but most of the time, worms remain in the digestive tract until the parasitic load is quite heavy, or they may only appear after your pet has taken a dewormer as the dead worms are eliminated. Regardless, heartworms do not live in the digestive tract at all, so your pet will never poop them out or cough them up. An animal with heartworm disease will typically show signs like trouble breathing, weight loss, and collapsing, but only after the heartworms have matured to an advanced stage. That’s why your pet has to be tested annually or any time they start on heartworm medication after going unprotected.