Although heartworm disease is preventable, it remains a significant threat to dogs and cats, and cases continue to rise. According to Embrace Pet Insurance data, heartworm diagnosis claims increased by more than 200% between 2020 and 2025.
The claims data also challenge common assumptions among pet owners about which pets are at risk. Heartworm disease is often associated with warm, humid regions where mosquitoes thrive year-round, and the highest incidence has historically been seen in the southeastern states. However, Embrace claims data show that heartworm diagnoses are not limited to traditional hotspots. Significant increases in claims were seen in many northern states, including Illinois, Michigan, Rhode Island, and Maine.
This data coincides with incidence maps published by the American Heartworm Society, which show a continuing northward expansion. The Companion Animal Parasite Council’s 2026 parasite forecast predicts that although the highest heartworm risk will remain in the southeastern U.S., spread will continue northward along the Mississippi River and up the East Coast, placing many central and eastern states at higher risk.
Based on diagnostic test reporting and epidemiologic data, the AHS estimates that more than 1.2 million dogs in the U.S. have heartworm disease.
Many pet owners assume that heartworm is only a risk during warmer months when mosquitoes are most active. However, Embrace claims data show that heartworm disease diagnoses are not limited to a specific season.
“This data reinforces what veterinarians see in practice,” said Dr. Julie Hunt, veterinary consultant for Embrace Pet Insurance. “Heartworm doesn’t depend on where a pet lives, what breed they are, or the time of year. 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.”
The data support the recommendation for year-round protection from the American Veterinary Medical Association, AHS, and other major veterinary organizations.
According to AHS President Dr. Marisa Ames, citing data from the organization’s 2025 veterinary survey, veterinarians reported recommending year-round prevention for 94% of canine patients. However, approximately 70% of veterinarians reported year-round compliance as a challenge, and 62% cited clients’ refusal to invest in heartworm prevention.
Embrace data also show that 79% of heartworm claims involved pets 4 years old or younger, with young adult dogs making up the largest portion of cases. Diagnoses were spread over a range of breeds and sizes.
According to the AHS, regularly communicating the importance of year-round prevention is critical.