Heartworm Cases Persist Nationwide According to U.S. Heartworm Incidence Survey

The 2025 American Heartworm Society Incidence Map uses shades of red to show that the southern and southeastern United States have the highest incidence of heartworm cases in dogs. Meanwhile, every state in the contiguous U.S. and Hawaii have colored area

The 2025 American Heartworm Society Incidence Map shows where heartworm cases were diagnosed in the 2025 calendar year.

American Heartworm Society releases new heartworm survey results

While heartworm disease continues to be far too common in the U.S., we can prevent our pets from becoming infected by using medications that are readily available from veterinarians.”

— Dr. Marisa Ames, President, American Heartworm Society

HOLLY SPRINGS, NC, UNITED STATES, May 4, 2026 /EINPresswire.com/ -- The results of the latest American Heartworm Society (AHS) heartworm incidence survey show that while heartworm disease in the U.S. is highly preventable in pets, it continues to be diagnosed nationwide. And while the disease is most common in warm and humid regions of the country, the survey showed that cases continue to spread into areas where the disease was once believed to be rare or nonexistent.

The non-profit AHS conducts a nationwide heartworm incidence survey of veterinary practices and animal shelters every three years, with veterinarians submitting data from dogs tested for the disease throughout the previous calendar year. In addition to pinpointing the most high-risk areas of the U.S. for heartworms, the survey also identified areas of the U.S. where infection rates increased since the survey was last conducted three years ago.

Heartworm cases are found nationwide
The southern and southeastern U.S. have historically been most closely associated with heartworm disease, a deadly disease that is spread to dogs and cats through the bite of infected mosquitoes. At any given time, the AHS estimates that heartworm disease affects more than a million pets in the U.S., with severe infections causing respiratory disease as well as heart and organ failure. According to the new AHS survey, the states with the highest incidence rates were Texas, Louisiana, Arkansas, Mississippi and South Carolina.

“Given that heartworms are transmitted by mosquitoes, it’s logical that regions with high mosquito populations and temperate, humid climates would have the highest rates,” said AHS president Dr. Marisa Ames, a veterinary cardiologist and assistant professor at the U.C. Davis College of Veterinary Medicine. However, she stressed that heartworms aren’t limited to these locales. Areas of east Texas, the Florida Panhandle, the central Carolinas and southern Illinois all went from “moderate” to “high” heartworm incidence in the survey, while southern California, southwest Colorado, east-central Wisconsin, western Virginia and southern Maine went from “low” to “moderate.” Meanwhile, several areas in the western and mountain western states, including central Washington, northern Idaho, northwest Nevada and southeast Wyoming, were considered new areas for heartworm infection.

Reducing heartworm incidence lies in human hands
Multiple factors can increase heartworm risk, according to Dr. Ames, including extreme weather events that trigger rapid growth in mosquito populations as well as the movement of heartworm-positive coyotes and other wildlife into urban and suburban areas. Despite these factors, the AHS president stressed that humans have the power to protect their four-legged family members from heartworms.

“While heartworm disease continues to be far too common in the U.S., we can prevent our pets from becoming infected by using medications that are readily available from veterinarians,” Dr. Ames concluded, adding that options include chewable, spot-on and injectable medications. “By giving heartworm medications year-round—and giving them on time—we can protect pets and significantly reduce the impact of this serious disease.”

About the American Heartworm Society
The mission of the American Heartworm Society is to lead the veterinary profession and the public in the understanding of heartworm disease. Founded during the Heartworm Symposium of 1974. The American Heartworm Society aims to further scientific progress in the study of heartworm disease, inform the membership of new developments and encourage and help promote effective procedures for the diagnosis, treatment, and prevention of heartworm disease.

Sue O'Brien
American Heartworm Society
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