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An Ounce of Prevention Is Worth A Pound Of Cure

Protect your pet from heartworms year-round

Photo of a woman hugging a dog.


The bad news: Heartworm disease can be fatal to dogs, cats, and ferrets. 
The good news: You can protect your pet from this disease.

An ounce of prevention is worth a pound of cure

Heartworms can infect your pet year-round and preventing them is much easier, and healthier, for your pet than getting heartworms in the first place or treating heartworm disease afterward. Year-round prevention is key to keeping your pet heartworm free. 

What are heartworms and how do pets get them

Heartworms are parasitic worms spread by infected mosquitoes. The parasites can cause severe disease and even death in dogs, cats, and other species of mammals, including ferrets. 

The heartworm larvae enter the pet’s body through the mosquito bite and then move into the bloodstream, eventually infecting the animal’s heart and lung arteries and growing up to 12-inches long.

The disease is not contagious from one pet to another, and heartworms in people are very rare.

Early signs of heartworm disease in pets are subtle and can be missed. As the disease progresses, pets may have a persistent cough, tiredness after mild to moderate activity, trouble breathing, and a decreased appetite. If left untreated, heartworm disease will damage the animal’s heart, lungs, liver, and kidneys, eventually causing death.

Use heartworm prevention medication year-round

Although there are fewer mosquitoes in the winter, there is still a risk that your pet could get heartworms if you stop giving heartworm prevention medication during this season. That’s one reason veterinarians strongly recommend pets receive heartworm prevention medication year-round. 

Veterinarians have reported heartworm disease in pets in all 50 states. Living in a state with a colder climate doesn’t mean that your pet is safe. Pets must have the proper amount of heartworm prevention medication in their blood for it to work correctly. If mosquitoes emerge early in the year, pets that haven’t received heartworm prevention medication during the winter run the risk of getting heartworms.

Depending on the animal species, heartworm prevention medications may come as oral, injectable, or topical products. However, they all only target heartworm larvae, not adults.

Dogs: Testing for heartworms is important

Be sure to ask your veterinarian to test your dog before starting or restarting a heartworm prevention medication. Dogs that have heartworms may not show symptoms right away, and your veterinarian can test your dog with a simple blood test.

And even if you’ve kept your dog on a steady regimen of heartworm prevention medication, yearly testing for the parasites is still recommended. No drug is 100% effective, and you want to make sure the drug is working. And sometimes life gets busy, and you may forget to give the heartworm prevention medication for too long, leaving your pet vulnerable to heartworms. 

Keeping your dog on heartworm prevention medication year-round, combined with annual testing, helps ensure any infection is caught promptly, thus minimizing harm to your dog from the infection.

If your dog becomes infected when he or she is not on a heartworm prevention medication and you later resume giving the medication without first testing your dog for heartworms, you may be putting him or her in danger.

Also, heartworm prevention medication will not kill adult heartworms, which will continue to reproduce. When a non-infected mosquito bites a heartworm-infected dog, the can mosquito become infected and can pass on heartworm larvae when it bites another unprotected dog, continuing the heartworm disease cycle. The goal of heartworm prevention medication is to kill heartworms at a very early stage inside the dog before they become adults and begin reproducing. Once a dog has adult heartworms, the worms have to be killed using an FDA-approved arsenic-containing drug, a potentially dangerous treatment process.

Cats and Ferrets: Indoor pets also need heartworm prevention medication

Mosquitoes can easily get into your home through open doors and windows. Even if your cat or ferret rarely or never goes outside, heartworm prevention medication is important. 

Heartworms don’t survive as well in cats as they do in dogs, but cats are still at risk for heartworm disease. However, diagnosing heartworms in cats is not as easy, and testing is not as simple, or accurate, as in dogs. In addition to blood work, testing in cats can include X-rays and ultrasounds.

Unlike for heartworm disease in dogs, there is no FDA-approved treatment for killing adult heartworms in cats. Because of the additional complications associated with diagnosing and treating cats, prevention becomes the best weapon against heartworms in cats. It’s best to place both indoor and outdoor cats on a year-round, FDA-approved medication to prevent heartworms.

Testing for heartworms in ferrets is also not as easy, simple, or reliable as in dogs. There is no FDA-approved treatment for killing adult heartworms in ferrets either, so prevention is critical.

Useful tips

  • Talk to your veterinarian about when and how often to test your pet for heartworms.
  • Talk to your veterinarian about which type of heartworm prevention medication is best for your pet. For example, if you have young children, be careful when using topical treatments, which are applied to the skin, and follow the directions carefully to minimize your child’s exposure.
  • Heartworm prevention medications are prescription only—so beware of internet sites or stores that will sell you these medications without a prescription.
  • The FDA monitors approved heartworm prevention medications for problems that may occur in pets, such as unexpected side effects. The FDA encourages you to work with your veterinarian to report any side effects to the drug company that manufactured the heartworm prevention medication. Please see How to Report Animal Drug and Device Side Effects and Product Problems.

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