My Dog Tested Positive for Heartworm: What Happens Now?

What heartworm disease actually does (and what I learned too late)

Looking back, I was searching my memory for any sign I might have missed — a persistent cough, shortness of breath, sudden fatigue on our walks, or a lack of appetite. But Jolie had shown zero symptoms. That’s the terrifying part about heartworm disease: by the time a dog shows physical signs like a swollen abdomen or a chronic cough, the worms (which can grow up to 14 inches inside the heart and lungs) have already done severe, long-term internal damage. These worms grow in a poor, infected dog’s heart, lungs, and pulmonary artery.

Mosquitoes infect dogs with heartworms through their bites, so warmer areas are more prevalent with this pest. Heartworms can live up to five years and can produce millions of offspring.

How missed preventatives snuck up on us

So, where did I go wrong? When I lived in New Orleans’ subtropical climate, it was a given that the dogs received heartworm preventative year-round. Moving to the Chicago area, I fell into a common trap: assuming winter cold meant safety. I thought skipping just a few colder months was a harmless way to minimize unnecessary medications. But microfilaria just need one active mosquito on a warm freak winter day.

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I didn’t notice any significant changes in my dog’s behavior. Because Jolie’s annual check-up included a routine blood screen before restarting her preventative, we caught it.

Still, if your dog is showing any unusual behavior or listlessness, head to your vet to follow up. The American Heartworm Society recommends a dog be tested annually. Doing so will ensure the infection can be detected quickly, minimizing damage caused by the disease.

Facing the risks of treatment

Once the initial shock wore off, panic set in about the treatment itself. The medical protocol for killing adult worms is intensive and physically taxing on a dog’s body.

If your dog tests positive, as my dog did, additional testing will be required to determine the severity of the infection. In some cases, your vet may need to perform an ultrasound to determine your dog’s ability to tolerate treatment.

Dr. Ashley Saunders, a veterinary cardiologist and professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences explains, “The recovery rate with treatment depends on how bad the disease is at the time it is treated and which treatment protocol is used,” She continues, “Dogs can recover following treatment, but those with severe damage may have long-term clinical signs or develop them at a later date.”

There are three stages of heartworms — adults, young adults, and microfilariae larvae — each requiring a unique treatment. By the time most dogs show signs of heartworm, they are typically already in advanced stages. Due to the life cycles of the worms, it takes anywhere from five to seven months for young heartworms to become detectable by a blood test.

Your vet will prescribe the best course of action. In addition, antibiotics and steroids will likely be necessary. Depending on the severity of the disease, the outlook may be grim. Some pets may even require a lifelong regimen due to these horrible worms, and, in other cases, dogs may only have mere months to live.

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The hard lesson: Why year-round prevention is non-negotiable

“Heartworm preventatives come in all forms that can be given orally as a tablet or beef chew, topically on the skin, or as an injection. There are also options for pets with food allergies or when it is difficult to give oral medications,” says Saunders. “Most preventatives also include medications against various other parasites, like hookworms, roundworms, fleas, ticks, and others. Consult your veterinarian to identify the best preventative for your pet.”

To think that for less than $50, I could’ve given my dog a few more doses of Heartgard (low-dose ivermectin) and kept her free of heartworms and the risky, expensive treatment required to kill them. Despite the growing trend to keep toxins to a minimum in dogs (and for a good reason), please give your dog monthly heartworm preventative year-round. The risk is not worth it.