A year after Jenn Beel lost her beloved 8-year-old Welsh corgi, Jack, to cancer, she found herself scanning dog profiles on Petfinder, hoping to find a new friend who might be as smart and sweet as Jack.

She found Louie, a young corgi-golden retriever mix being fostered by K-9 Lifesavers, a rescue group in Stafford, Virginia. He had the cutest face she’d ever seen. “I saw his picture and was in love,” says Beel, senior creative director at the Humane Society of the United States. She immediately emailed the rescue to ask if Louie was still available.

He was, but there was a hitch. Louie had tested positive for heartworm disease, a potentially fatal condition.

Illustration of a mosquito
The time it takes (at a minimum) for dogs to test positive after they have been infected.

Heartworms are just what they sound like—worms up to a foot long that live and reproduce in the host’s heart. Dogs may be asymptomatic at first, but as the parasites multiply, they cause lethargy, loss of appetite, coughing and difficulty breathing. If left untreated, the infection damages the heart, arteries, lungs and other organs, and can ultimately lead to congestive heart failure.

Mosquitoes are the vector for heartworms, carrying larvae from dog to dog. As mosquitoes thrive in hot, humid environments, it’s no surprise that heartworm is rampant in the southern U.S.—Mississippi, Louisiana, Arkansas, Texas and Tennessee have the highest rates of infection, according to the American Heartworm Society.

But living in a cold weather area doesn’t protect dogs from heartworm; it’s been diagnosed in all 50 states. Many veterinary epidemiologists believe that climate change is a factor in the rise of heartworm throughout the country. Many regions are experiencing longer, warmer summers, higher humidity and increased rainfall, all of which suit the mosquito just fine.

Treatment has a high success rate, but it’s not a quick process: The larvae and worms exist in varying stages, and timing is everything in ensuring that every stage is eradicated.

Immiticide and ivermectin are the drugs commonly used to kill heartworms, and treatment has a high success rate. But it’s not a quick process: The larvae and worms exist in varying stages, and timing is everything in ensuring that every stage is eradicated. Immiticide injections are effective, but only on adult worms and late-stage larvae, says Dr. Gary Block with Ocean State Veterinary Specialists in Rhode Island. Ivermectin (the ingredient found in most preventatives) targets immature larvae and microfilaria (the early life form of the parasite).

At the Crofton Veterinary Center in Maryland, the treatment regimen typically goes like this, says Dr. Cynthia Harker: “We’ll start them on heartworm prevention to kill microfilaria and prevent spread, [then] we’ll start them on antibiotic” to kill bacteria that live with the heartworm. That’s followed by Immiticide injections over the course of several months to kill adult worms.

Portrait of Louie the dog in his therapy vest
Louie is now a proud therapy dog.
Meredith Lee

The hardest part of the whole process, particularly for young, rambunctious dogs who live to play, is the two- to four-month exercise restriction, which is critical while the worms are dying. No jumping or running or rough-housing allowed. “If they get too excited and have a massive worm die-off, they could get pulmonary emboli or anaphylaxis that could cause sudden death,” explains Harker.

The best defense in warding off heartworm is a good offense—keeping up with blood testing (annual tests are typically recommended) and consistent dosing with heartworm preventative. The preventative is available in chewable treats (or included in some topical flea-prevention medications) given once a month or as injections that last for six to 12 months. Some owners discontinue the preventative during winter months when mosquitoes aren’t active, but Harker cautions against that approach: It can be hard to judge when it’s safe to discontinue the medicine and easy to forget to start giving it again before the weather warms up. Considering that the cost of heartworm treatment can easily run $400 to $800, it’s far less expensive to maintain the preventative, which usually runs less than $10 a month.

Louie, Jenn and Charlie at Louie's Luau to celebrate the end of his heartworm treatment
Jennifer Beel and Charlie Webster celebrate the end of Louie’s heartworm treatment.
Courtesy of Jennifer Beel

Beel knew little about heartworm when she first saw Louie’s photo, but she wasn’t going to let a treatable medical issue stand in the way of true love. Her boyfriend, Charlie Webster, wasn’t so sure. He asked if she really wanted to go through the months of treatment. “I said, ‘Every dog has problems. If his personality is good, then that’s the most important thing.’ ” When Webster met Louie at an adoption fair, where he was basking in the undivided attention of some Girl Scouts, he agreed. Louie was the dog for them.

Louie’s heartworm treatment was uneventful. “The rescue was very good about explaining things, reassuring us that he was young and there wouldn’t be aftereffects,” says Beel. “They put my mind at ease.” The treatment costs were also covered by K-9 Lifesavers, which—like many shelters and rescues—holds regular fundraisers to cover the expenses of its heartworm-positive dogs.

To celebrate the end of his treatment, Beel held a party, Louie’s Labor Day Luau, to introduce him to her friends and family.

Four years on, Louie is healthy, happy and eager to share his love with the world. He’s become a therapy dog, visiting nursing homes, group homes and kids’ reading programs at the local library. Beel and Webster are forever grateful that they didn’t let heartworm deter them from adopting such a good-hearted dog.

Arna Cohen is a former staff writer for All Animals.

Green dog iconWhat are the symptoms of heartworm?

  • Mild persistent cough.
  • Reluctance to exercise.
  • Fatigue after moderate activity.
  • Decreased appetite.
  • Weight loss.
  • Excess fluid in abdomen.
  • Heart failure.
  • Cardiovascular collapse.

Green cats iconCan cats get heartworm?

While heartworm is commonly associated with dogs, cats aren’t completely off the hook. Felines “are an aberrant host,” says veterinarian Cynthia Harker. “Most times the cat’s immune system will destroy the heartworms before they become a problem.” But there’s no heartworm treatment for cats, and sometimes a cat will succumb, which is why some vets recommend monthly preventatives for their feline patients.

LEARN MORE: Find heartworm-related resources for pet owners and read more about the disease in dogs and cats.

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This article was written and produced by the team behind All Animals, our award-winning magazine. Each issue is packed with inspiring stories about how we are changing the world for animals together.

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