Are your clients underestimating heartworm risk?

Heartworm disease may be far more widespread and far less predictable than many pet owners assume. New claims data from Embrace Pet Insurance shows that heartworm diagnosis claims increased 201% between 2020 and 2025, a trend the company says challenges common assumptions about which pets are at risk and where the disease is most likely to occur.¹

Although heartworm has historically been concentrated in the Southern US, Embrace's data show diagnoses occurring across the country and throughout the calendar year, indicating that risk is no longer confined to traditional hot spots or peak mosquito season. Notably, several states outside those historic hot spots, including Illinois, Michigan, Rhode Island, and Maine, saw substantial increases in heartworm claims.¹

The findings track with broader surveillance data. The American Veterinary Medical Association has reported that heartworm prevalence has climbed over the past 2 decades despite the wide availability of effective preventives, and a 2025 incidence survey by the American Heartworm Society (AHS) similarly found the disease spreading beyond its traditional range and into areas once considered lower risk.^2,3

Not just a summer problem

A common misconception among pet owners is that heartworm risk tracks closely with warm-weather mosquito season. Embrace's claims data complicate that assumption, showing diagnoses occurring year-round rather than clustering in summer months.

"[These] data reinforce what veterinarians see in practice. Heartworm doesn't depend on where a pet lives, what breed they are, or the time of year," said Julie Hunt, DVM, veterinary consultant for Embrace Pet Insurance. "Because the disease is so preventable, the biggest risk factor is inconsistent protection. Staying on year-round prevention helps close the gaps that allow heartworm to take hold."

Heartworm is transmitted exclusively through the bite of an infected mosquito and can affect both dogs and cats. Once established, worms can live in the heart, lungs, and associated blood vessels, potentially causing severe lung disease, heart failure, organ damage, and death. Because clinical signs often don't appear until the disease has progressed, routine testing alongside consistent preventive use remains essential. The AHS estimates more than 1 million dogs in the US are currently infected.^3,4

Geography and age are no guarantee

The AHS has diagnosed heartworm in every state, and recent incidence surveys continue to flag emerging areas of concern outside the traditional Southern hot spots, meaning no region can be considered entirely risk-free.³

Age also appears to offer little protection. Embrace found that 79% of heartworm claims involved pets aged 4 years or younger, with young adult dogs accounting for the largest share of cases. Diagnoses spanned a wide range of breeds and sizes, suggesting susceptibility isn’t limited to any particular type of dog.¹

For veterinary teams, the data underscore a familiar message with renewed urgency: Client conversations about heartworm prevention shouldn't be limited by geography, season, or a pet's age. As Embrace's findings suggest, consistent, year-round prevention remains the most reliable safeguard against a disease that continues to show up in unexpected places.

References

1. Embrace Pet Insurance. Internal claims data (2020-2025).
2. Larkin M. Heartworm incidence climbs despite preventive efforts. American Veterinary Medical Association. October 8, 2024. Accessed June 30, 2026. https://www.avma.org/news/heartworm-incidence-climbs-despite-preventive-efforts
3. American Heartworm Society releases new heartworm incidence map. American Heartworm Society. April 7, 2026. Accessed June 30, 2026. https://www.heartwormsociety.org/in-the-news/977-american-heartworm-society-releases-new-heartworm-incidence-map
4. Heartworm prevention for dogs. American Heartworm Society. Accessed June 30, 2026. https://www.heartwormsociety.org/pet-owner-resources/heartworm-prevention-for-dogs