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Why is Heartworm Risk Increasing in the United States?

By JoAnna Pendergrass, DVM
published: August 20, 2019 - updated: April 22, 2022 • 3 min. read
small dog at the vet

If you’re a dog parent, you probably know about heartworm disease. Your veterinarian has stressed the importance of year-round heartworm prevention and annual heartworm testing to keep your dog heartworm-free.

Given how much the veterinary community has championed heartworm prevention for years, you’d think that the disease wouldn’t be a big problem. But it is. Heartworm incidence is expected to increase in 2019, continuing a trend of yearly increased incidence since 2013.

Why is that? Why are more dogs getting heartworm disease when veterinarians are doing all they can to prevent it? What can you do to prevent your dog from getting heartworms?

Heartworm Basics

Before answering those questions, let’s talk a bit about the disease itself. Heartworm disease is caused by Dirofilaria immitis, a parasite that is carried by mosquitoes. When an infected mosquito bites a dog, little D. immitis larvae enter the blood and mature into adults within about six months. The adults can live for 5 to 7 years and cause a range of clinical signs, including coughing, exercise reluctance, weight loss, and, once heart failure sets in, a fluid-swollen belly.

Heartworm disease is treatable, but the treatment is expensive and requires strict avoidance of exercise. Unfortunately, after going through treatment, some dogs aren’t as happy and carefree as they used to be.

Protect your pet

Why is Heartworm Incidence Increasing?

Historically, heartworm disease has been most problematic in the southern and southeastern United States. Two main factors contribute to increased heartworm risk throughout the country: climate change and cross-country dog transportation.

Climate change. Warmer temperatures and increased humidity across the country increase mosquito breeding, which can increase the likelihood of mosquitoes carrying D. immitis. Milder winters mean that mosquitoes don’t die off as they usually would in cold temperatures, keeping the mosquito population higher than it should be in the winter.

Cross-country dog transportation. Dogs are increasingly transported across state lines for several reasons, one of which is natural disasters in heartworm-endemic areas. When Hurricane Katrina struck New Orleans in 2005, for example, animal welfare organizations rescued dogs from the hurricane, then transported and adopted them out across the country; Louisiana is endemic for heartworms.

As reported by a study in Animals journal, animal welfare organizations do not routinely test or treat rescued dogs for heartworms or administer heartworm preventatives before transporting the dogs. Thus, transported dogs who are heartworm positive can spread the disease to wherever they are going. It is possible that dogs rescued from Hurricane Katrina spread heartworm disease to their new location.

A second reason for increased dog transportation is the effort to reduce euthanasia and increase adoption of shelter dogs. If dogs are not tested and treated for heartworms before being adopted out, they could introduce heartworm into their new community, which could be in a different part of the country.

What Can You Do About Heartworm?

By now, you may be wondering if heartworm disease is going to come knocking on your door. Fortunately, despite the increased risk of heartworm disease across the country, heartworm prevention remains practical and easy to do. Follow these prevention strategies:

  • Be aware of heartworm incidence where you live. This awareness is especially important if you live in an area that, historically, is not endemic for heartworms. Talk to your veterinarian about heartworm risk in your area. You can also look at the heartworm prevalence map at the Companion Animal Parasite Council website.
  • Limit your dog’s mosquito exposure. Keep your dog indoors during peak mosquito times: dawn and dusk. Also, remove any potential mosquito breeding spots around your home, such as birdbaths or empty flower pots that hold standing, stagnant water.
  • Administer year-round heartworm prevention. With rising temperatures, mosquitoes are problematic for longer during the year. Give all of your pets (even your cats!) a monthly heartworm preventative.
  • Get your dog tested for heartworms each year.

Concluding Thoughts about Heartworm

Although heartworm disease is on the rise for several reasons, it is also easily preventable. Do your part by being proactive about preventing heartworm disease in your pet.

Content provided by JoAnna Pendergrass, DVM. Dr. Pendergrass is owner and founder of JPen Communications, a medical communications company specializing in consumer education.

Beating heartworm is tough enough – with Healthy Paws, pet parents don’t have to choose between their pet and their wallet. By signing up for pet insurance when pets are young, ongoing treatments will be covered up to 90%. Find out more by getting a free quote.

joanna pendergrass
By JoAnna Pendergrass, DVM

JoAnna Pendergrass, DVM, is a veterinarian and freelance medical writer in Atlanta, GA. After graduating from the Virginia-Maryland College of Veterinary Medicine with her veterinary degree, JoAnna completed a 2-year research fellowship in neuroscience at Emory University. During this fellowship, she learned that she could make a career out of combining her loves of science and writing. As a medical writer, JoAnna is passionate about providing pet parents at Healthy Paws with clear, concise, and engaging information about pet care. Through her writing, she strives not only to educate pet parents, but also empower them to make good health decisions for their pets. JoAnna is a member of the American Medical Writers Association.

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