What Is Heartworm and How Can You Protect Your Pet From It?

Heartworms are parasitic worms that can grow to 12 inches in length. The larvae can enter a pet’s body through mosquito bites and move through the bloodstream to infect the animal’s heart and lung arteries.

Though the disease can’t spread between pets, mosquitos can continue to spread it after biting infected pets.

Heartworms in people are very rare, the FDA noted.

The early signs of heartworm disease are subtle and can be overlooked: They include a mild cough, decreased appetite and weight loss. Later disease includes a persistent cough, tiredness after mild to moderate activity, trouble breathing and a decreased appetite. Heartworm disease can damage the animal’s heart, lungs, liver and kidneys.

Heartworm infections happen year-round and in all 50 states, including in colder climates.

Pets must have the proper amount of heartworm prevention medication in their blood for it to work correctly when mosquitoes emerge. Medications only target heartworm larvae, not adults.

If you have a dog: Have your dog tested before starting medication, which can be done with a simple blood test.

Even if your dog has regularly taken heartworm medication, testing is still important. That's because no drug is 100% effective and it's important to make sure the drug has been working and that any delays in giving your dog the medication have not left it vulnerable to the disease.

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

Killing adult heartworms requires using an FDA-approved arsenic-containing drug, a potentially dangerous treatment process.

Indoor pets also need heartworm treatment because mosquitos can find their way inside through open doors and windows.

If you have a cat: Heartworms don’t survive as well in cats as they do in dogs, but cats are still at risk for heartworm disease, according to the FDA. Diagnosing the disease is more challenging. In addition to blood work, testing in cats can include X-rays and ultrasounds.

No FDA-approved treatment for killing adult heartworms exists for cats. This creates additional complications for diagnosing and treating cats, so prevention is important year-round.

If you have a ferret: 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.

The FDA suggests talking to your veterinarian about when and how often to test your pet for heartworms and about which type of heartworm prevention medication is best for your pet.

Topical treatments may not be best for pets that are around young children, for example.

Heartworm prevention medications are prescription only. Beware of internet sites or stores that will sell you these medications without a prescription, the FDA warned.

More information

The American Veterinary Medical Association has more on heartworm disease.

SOURCE: U.S. Food and Drug Administration, news release, Jan. 24, 2023