Heartworm spreads beyond the South as new U.S. survey shows rising risk areas

By AI, Created 11:24 AM UTC, May 20, 2026, /AGP/ – The American Heartworm Society’s latest nationwide survey finds heartworm disease remains common across the U.S. and is expanding into places once considered low-risk. The results highlight where cases are rising and reinforce the need for year-round prevention in pets.

Why it matters: - Heartworm disease is highly preventable, but the latest survey shows it still affects pets nationwide. - The findings point to growing risk outside the South and Southeast, where many pet owners may not expect heartworm exposure. - The disease can cause respiratory illness and, in severe cases, heart and organ failure.

What happened: - The American Heartworm Society released new results from its nationwide heartworm incidence survey on May 4, 2026. - The non-profit surveys veterinary practices and animal shelters every three years. - Veterinarians submit data from dogs tested during the previous calendar year. - The survey identified the highest-incidence states as Texas, Louisiana, Arkansas, Mississippi and South Carolina.

The details: - The American Heartworm Society estimates that heartworm disease affects more than a million pets in the U.S. at any given time. - Heartworm disease spreads to dogs and cats through the bite of infected mosquitoes. - East Texas, the Florida Panhandle, the central Carolinas and southern Illinois moved from moderate to high incidence. - Southern California, southwest Colorado, east-central Wisconsin, western Virginia and southern Maine moved from low to moderate incidence. - Central Washington, northern Idaho, northwest Nevada and southeast Wyoming were identified as new areas for heartworm infection. - Dr. Marisa Ames, the American Heartworm Society president, said high mosquito populations and temperate, humid climates help explain higher rates. - Dr. Ames said extreme weather events can rapidly increase mosquito populations. - Dr. Ames also said heartworm-positive coyotes and other wildlife moving into urban and suburban areas can raise risk. - The survey is designed to map high-risk areas and track changes in infection rates over time.

Between the lines: - The survey suggests heartworm risk is broadening as climate and wildlife patterns shift. - That makes prevention a national issue, not just a regional one. - The findings also show that pet owners in lower-incidence states may need to rethink how they assess risk.

What’s next: - The American Heartworm Society is urging pet owners to use heartworm prevention medications available from veterinarians. - Dr. Ames said options include chewable, spot-on and injectable medications. - Dr. Ames said year-round dosing, given on time, can significantly reduce the impact of the disease. - The survey will continue on its three-year cycle, creating the next snapshot of national risk patterns.

The bottom line: - Heartworm is still widespread, and the map of risk is getting bigger. Year-round prevention remains the clearest defense for pets.