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My Dog Is Heartworm Positive: Signs, Diagnosis, and Treatments

If heartworm happened to my dog, it can happen to yours.

by Julia Lane, CPDT-KA
September 1, 2019
a Dalmation with heartworms comforted by owner
Photo: Helena Lopes / Pexels

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My vet can't remember the last time she had a heartworm-positive case. Until now. My 8-year-old Dalmatian, Jolie, tested positive for heartworms at her annual checkup. We retested the blood in hopes that it was a false positive. But there was no need to send the sample back to the lab. Through a microscope, my vet could see microfilaria swimming in her blood sample. Obviously, I was shocked and upset because I take excellent care of our dog — how could this have happened? 

What is Heartworm in Dogs?

Heartworm in dogs (dirofilariasis) is a serious and potentially fatal disease caused by a parasitic Dirofilaria worm that grows up to 14 inches long. These worms grow to live in a poor infected dog’s heart, lungs, and pulmonary artery. Mosquitos 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. This disease causes long-term damage to a dog’s internal organs, so it’s crucial to use heartworm prevention medications. If you’re wondering how you can tell if a dog’s got heartworms, here are some of the signs:

Symptoms

  • Mild persistent cough

  • Shortness of breath

  • Fatigue

  • Resistant to exercise

  • Decreased appetite

  • Swollen belly due to fluid accumulating in the abdomen

  • Nose bleeds

  • Sudden death

How is Heartworm Disease Diagnosed?

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. But, despite now living in the Chicago area, I learned that you to give your dog heartworm preventative through the winter, not just the warmer months.

I didn’t notice any significant changes in my dog’s behavior. But, before administering preventative medication, vets will perform a simple blood test. 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. 

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.

How Risky is the 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 heartworm to become detectable by a blood test.

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. 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 life-long regimen due to these horrible worms, and, in other cases, dogs may only have mere months to live.

Can You Prevent Heartworm in dogs?

“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.

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Julia Lane, CPDT-KA

Julia Lane owns Spot On K9 Sports, a training facility in the Chicago area, and offers online dog-sport coaching. She is the author of several travel books, and her byline has appeared in The New York Times Magazine, Poets & Writers and elsewhere.