- Texas ranked No. 1 in heartworm incidence for the first time, followed by Louisiana, Arkansas, Mississippi and South Carolina.
- New hotspots with more than 100 cases per clinic were identified in east Texas, the Florida Panhandle, southwest Florida, the central Carolinas and southern Illinois.
- Heartworm cases are expanding into moderate- and lower-incidence regions across the West, Midwest and Northeast.
The American Heartworm Society has released its latest nationwide canine heartworm incidence survey and accompanying incidence map, revealing that the highest rates of heartworm disease remain concentrated in traditional Gulf Coast and southeastern U.S. strongholds. However, the survey also highlights concerning geographic expansion into cooler and drier regions.
Conducted every three years, the AHS Incidence Survey compiles data from veterinary practices and shelters that submit canine heartworm antigen test results from the previous year. The most recent survey, completed in early 2026, reflects testing performed throughout 2025.
Texas Moves to the Top
For the first time, Texas led the nation in reported heartworm incidence. According to AHS President Marisa Ames, the next highest-incidence states were Louisiana, Arkansas, Mississippi and South Carolina.
The remaining top 10 states included Tennessee, Alabama, North Carolina, Florida and Georgia.
Areas reporting more than 100 diagnosed cases per clinic included east Texas, the Florida Panhandle, southwest Florida, the central Carolinas and southern Illinois.
Cases Spread Beyond Traditional Hotspots
The survey found expanding moderate-incidence zones—defined as 6 to 25 cases per clinic—in southern California, southwest Colorado, east-central Wisconsin, western Virginia and southern Maine.
Several western and mountain western areas also saw annual cases rise from fewer than one case per clinic in the previous survey to three to five cases per clinic, including central Washington, northern Idaho, northwest Nevada and southeast Wyoming.
Prevention Remains Critical
Nearly 60% of surveyed practitioners said heartworm incidence rates had remained stable since 2023, while 19% reported increases and 22% reported decreases. Dr. Ames emphasized that although heartworm remains a serious nationwide threat, it is almost entirely preventable with year-round prevention.
The updated AHS incidence map is now available for download and can be compared with maps published every three years since 2001.
Information sourced from the company’s press release.
