Partners in Heartworm Prevention


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Whether it’s at the national stakeholder level or locally in his veterinary practice, Dr. Chris Duke, AHS president, continues to advocate for ongoing veterinary care that includes heartworm prevention.

In his almost 40 years of practicing veterinary medicine, Chris Duke, DVM, is all too familiar with the trauma that heartworms can inflict on pets. Even if a heartworm-positive dog is asymptomatic, Duke said there is “quiet” damage going on within the pulmonary vessels and the lung parenchyma. “Unless a heartworm-positive case is treated, the damage only advances over time as the worm numbers grow and the damage is compounded,” he said. “That is when cases become symptomatic, unfortunately to the point of potential death of the dog.”

If a dog is treated for heartworms, the worms of course die out, but many times the dead fragments of the worms may stay embedded in the pulmonary tissues for years, he said.  Although cleared on the antigen tests within a year, Duke has had some of these dogs remain as “chronic coughers” because of the damage that remained. This is because of the scarring and fibrosis of the affected tissues.

However, most dogs that Duke treats handle the treatment well, utilizing the AHS Guidelines, and remain symptom-free long term. “We of course follow up on these dogs through routine preventive health visits, maintain annual heartworm testing, and assure that lifelong heartworm prevention is maintained.”

Then and now

As president of the American Heartworm Society, Duke is on a mission to educate pet owners and veterinary medicine stakeholders at large on the importance of heartworm prevention. As a local practitioner and co-owner of Bienville Animal Medical Center in Ocean Springs, Mississippi, Duke said most pet owners in the Gulf Coast region that he talks to are aware of the problems and challenges regarding the heartworm disease threat. “Occasionally I have to ‘begin the education’ when a heartworm positive case is diagnosed,” he said, “but as we all know, the best time to get the clients educated is on a puppy visit.” That is when heartworm prevention should begin. Duke said the AHS pamphlets are excellent tools for owner compliance. “Particularly the incidence map makes selling heartworm prevention product for puppies and heartworm-negative dogs easy.”

Duke seldom receives pushback on the issue of heartworm prevention compliance in the exam rooms. “Once I educate clients and illustrate the need for heartworm prevention, my clients give me agreement on this issue,” he said. “Where I run into trouble is when clients either run out of product or say they’ll order it online – then fail to follow through. That’s when we get the surprise positive antigen heartworm test result the following year.”

Occasionally, Duke will hear that “times were tough” and clients experienced economic constraints for a time, but usually clients just admit to falling off the prevention wagon. “I also hear the ‘indoor dog’ argument from time to time,” he said. “But when I drill down and ask about outdoor bathroom breaks, outdoor playtime, and so forth, they get my point. Prevention against heartworms is worth a pound of cure, and the associated risk and expense.”

When it comes to compliance, Duke said it’s hard to compare apples to apples from when he started practicing in the early 1980s because the heartworm prevention products have changed so much. “Back in that day we would try and start puppies on daily prevention products like Filaribits or Styrid Caricide (diethycarbazine products),” he said. “Then in the mid-80s, we saw the advent of Heartgard, which allowed for monthly dosing. Fast-forward to today, and we have a fine array of monthly chewable and topical products, some of which also enable pet owners to prevent fleas, ticks and other parasites as well. We also have effective injectable heartworm prevention medications that can be given either every six months or annually.”

One would think that with such an arsenal of weapons to protect these dogs, we should see higher compliance. Yet, Duke said his practice saw 240 cases of heartworm disease in 2021 alone. “We still diagnose many heartworm-positive cases in our practice,” he said. “In almost all of these, clients admit to non-compliance. In spite of our best efforts, others still require education about the importance of protecting their dogs against heartworms.”


Illustration for heartworm symptoms in cats


Diagnostics is another area where it is difficult to compare apples to apples, Duke said, given modern heartworm antigen testing methods versus the 80s microfilaria-based tests. Antigen testing became the practiced norm by the early 90s and indeed revealed more heartworm-positive dogs because the test was so much more accurate. Many antigen-positive dogs with heartworms are void of microfilaria, so better testing was needed. “In my case, the practice size also increased throughout the 90s and into the new millennium,” he said. “We now have eight veterinarians vs. one or two in our practice, and we are conducting tests constantly throughout each practice day. We see more cases because we are providing services to so many more dogs and we are treating more cases.”

As to heartworm cases amid the pandemic, Duke said we will likely be studying the overall effects of the pandemic on pet health for some time. The AHS has conducted several online veterinary surveys since the start of the pandemic, the latest in June 2021, to see how practices and shelters were coping with the pandemic and if there were data shifts in heartworm-related topics. More than 500 respondents from 44 U.S. states and Canadian provinces shared their trends. At that time, two-thirds of respondents reported that the heartworm numbers they were seeing were about the same compared with other years. The remainder were twice as likely to report increases as decreases.

“Meanwhile, one in five said they were seeing some erosion in pet owner compliance with heartworm prevention, due to changes in client income and gaps in owner knowledge about heartworm prevention,” Duke said. “One-third reported having clients that were delaying heartworm testing. Again, those numbers were from last June, so it will be interesting to see how things change as we continue to move forward.”


Illustration of heartworm symptoms for dogs.


Supportive stakeholders

The animal health industry overall is very supportive of best practices that support the well-being of pets, and the AHS enjoys good relationships with pharmaceutical and diagnostic companies as well as many other veterinary and pet owner organizations that provide products and services and/or educate about veterinary/pet care, Duke said. “It is essential that owners provide their pets with ongoing veterinary care to ensure they undergo routine heartworm testing and are prescribed heartworm preventives,” he said. “The more we can all work toward a common goal of educating owners about this serious but preventable disease, the better.”

This includes companies that make or sell pet foods, snacks, toys and other pet-related purchases, as well as the many types of media, websites and social media entities that communicate about pet health.

“At the AHS, we are sometimes invited by manufacturers in non-pharmaceutical venues to preach the message of prevention, and are always open to these opportunities,” Duke said. “We are all partners in helping to prevent, diagnose and treat heartworm disease and we all share a common goal of maintaining the good health of pets everywhere.”


Infographic of when you should text your dog for heartworms.


Think 12 Heartworm Prevention Resources

Think 12 is an ongoing initiative through which the American Heartworm Society provides educational materials, including articles, fact sheets, posters, videos and other tools that help pet owners understand the need to administer heartworm preventives 12 months a year and test pets for heartworm every 12 months. Year-round prevention and annual testing are recommended by American Heartworm Society and form the foundation of their guidelines for heartworm prevention and diagnosis.

New Think 12 materials and tools are produced each month and are made available to veterinary professionals and pet owners free of charge. Think 12 materials can be downloaded and displayed, printed as handouts – or used in clinic newsletters or on social media platforms.

Check the Think 12 Resource Center frequently for new materials at


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