A Guide to Adopting a Dog With Heartworms
A positive heartworm diagnosis can sound scary, but experts say there’s no reason to worry.
Warmer winters, natural disasters that displace pets, and increased movement of rescued animals across borders have all contributed to a rise in heartworm disease across the U.S. This means more shelter dogs are testing positive for heartworm disease—leaving heartworm-positive pups in need of loving homes and proper treatment.
What does it mean if a dog is heartworm-positive?
You fell in love with a pup, but they’re heartworm positive or currently being treated for heartworms. Is that a dealbreaker? It shouldn’t be. Megan Miller, manager at FurPetVo Sanctuary’s Dogtown, reassures us that heartworm-positive dogs:
- Are not contagious to other pets
- Can be treated—and many don’t experience complications
- Can live normal lives when infections are not severe
- Deserve loving homes, even if a severe infection means a shorter lifespan
What are heartworms?
Heartworms (Dirofilaria immitis) are parasitic worms that feed on the blood of animals, including dogs, cats, and ferrets. Once an adult worm infects a host, it lives within the heart, major blood vessels, and lungs, explains Dr. Rebecca Greenstein, DVM, veterinarian at Kleinburg Veterinary Hospital.
Without treatment, adult heartworms can grow to over a foot in length and become deadly. It’s scary stuff—but, “It’s not hard to prevent heartworm infections,” says Dr. Elizabeth Clyde, a small-animal veterinarian and board member of the American Heartworm Society (AHS).
What causes heartworm in dogs?
“Mosquitos!” cause heartworm in dogs, Dr. Clyde says. As if mosquitos weren’t annoying enough, they can carry heartworm larvae. When they bite a dog, the larvae enter the dog’s bloodstream, where they mature into adult worms—unless the dog is on year-round parasite preventative.
What are the symptoms of heartworms in dogs?
Heartworms are so damaging because they migrate through tissue and into the pulmonary vessels—the blood vessels that carry blood from the heart to the lungs.
“The larvae are doing their best to get to the heart,” Dr. Clyde says. “But as the heart beats, it pushes them back into the lungs.” This constant back-and-forth friction damages the vessels, leading to symptoms such as:
- Coughing
- Tiring quickly
- Collapsing or fainting episodes
- Decreased appetite
- Weight loss
Treating a heartworm-positive dog
Heartworms can be treated in dogs, but the damage they’ve caused can’t be undone.
Treatment options
According to the American Heartworm Society, there’s only one drug approved by the U.S. Food and Drug Administration (FDA) for treating heartworms in dogs: Melarsomine (also called Immiticide or Diroban). It’s administered via a series of injections by a licensed veterinarian and typically clears the infection in one to three months.
The cost to treat a heartworm-positive dog ranges from $500 to $1,500. Some shelters and rescues—including FurPetVo—cover this cost, while others do not.
For instance, FurPetVo treats heartworm-positive dogs as soon as they arrive at the shelter. Other organizations, like Austin Pets Alive!, wait until the dog is adopted or placed in foster care before beginning treatment. This approach reduces stress during recovery and can minimize treatment complications, says Dr. Rachel Gordan, DVM, a veterinarian at Austin Pets Alive!.
When a shelter or rescue can’t cover the cost of heartworm treatment, there are other ways to manage veterinary expenses, including:
- Discussing payment plans and lower-cost appointment options with your veterinarian
- Seeking financial assistance from nonprofits or charities
- Applying for financing through services such as CareCredit
- Fundraising using platforms like GoFundMe
Supporting your dog through recovery
Melarsomine can have serious side effects—but these risks are significantly minimized when a veterinarian administers the injections correctly. Never give this medication to your dog yourself.
Another risk is that dead worms can sometimes block blood flow—similar to a blood clot. According to the American Heartworm Society, limiting your pup’s exercise and excitement for six to eight weeks following the final injection helps minimize this risk. That means:
- Crate rest and no unsupervised roaming in the house or yard
- Short potty walks only, on a leash in the backyard
- No playing or training that gets them excited—including limited excitement from other household pets
Adopting a heartworm-positive dog
Megan Miller says FurPetVo and its shelter partners always share as much as they know about a dog’s medical and behavioral history with potential adopters—including whether the pup is heartworm-positive or has been treated previously. “Transparency is crucial to successful adoptions—it ensures potential adopters have all the information they need before committing to bringing home a pet,” she says.
If you’re interested in adopting a heartworm-positive dog, here are some important things to consider:
- Heartworm disease is treatable, but the damage is irreversible. Severe infections may limit a dog’s athletic ability and potentially shorten their lifespan.
- Treatment can have serious side effects and requires strict rest for recovery.
- Treatment costs $500 to $1,500, and some shelters may not cover it.
- A heartworm-positive dog cannot spread heartworms to another pet or to humans.
- Dogs can become reinfected with heartworms if they’re not on year-round preventive medicine.
- Heartworm-positive dogs are an at-risk population in desperate need of adopters and foster parents. “Shelters across the country are struggling with overcrowding,” Miller explains. “Sadly, heartworm-positive dogs are the first to be euthanized when capacity becomes an issue.”
Preventing heartworms in your adopted pet
Heartworm is a nasty parasite that can infect both cats and dogs. Unfortunately, treatment is only available for dogs. The good news? Heartworm disease is preventable.
Here’s how to keep your new pet safe from heartworms:
- Year-round parasite prevention. No matter where you live, keep your pet on year-round heartworm prevention medication. Most prescription flea medications offer all-in-one protection against fleas, ticks, roundworms, and heartworms.
- Get your dog tested. Test your dog annually for heartworms. It’s a simple blood test ($45–$100) your regular veterinarian can perform.
Commonly asked questions
How common are heartworms in dogs?
In 2023, about one percent of dogs in the U.S. tested for the parasite were shown to be heartworm positive. It’s important to consider that this number likely underestimates the true prevalence. In addition to untested or untreated cases, Dr. Clyde explains that it takes about six months for heartworms to mature and become detectable in tests—which means some infected dogs might initially test negative. Heartworm is a threat in all 50 states, so prevention no matter where you live is crucial.
Are heartworms contagious in dogs?
You don’t need to worry about a dog passing heartworms to other dogs, Dr. Greenstein says. A mosquito would need to bite an infected dog and then bite a healthy dog to potentially transmit the parasite.
