August 01, 2020

Heartworm disease became more common in hot spots across the U.S. and remained prevalent in the Southeast, Gulf Coast, and lower Mississippi Valley.

Dr. Chris Duke, president of the American Heartworm Society, said the organization’s 2019 survey showed rising numbers of infections with Dirofilaria immitis in Boston, Chicago, Las Vegas, and Minneapolis, as well as in smaller cities such as Durant, Oklahoma, and Redding, California.

Dr. Doug Carithers, AHS vice president and longtime survey chair, said those hot spots are often associated with animal movement, including when dogs move from shelters in high-incidence areas to shelters in low-incidence areas. He’s glad shelters and veterinarians identified the infections reported in the survey because, without testing and preventive use, mosquitoes around the dogs’ new homes could have spread heartworm disease throughout entire neighborhoods.

“Veterinarians and staff typically feel really comfortable in understanding heartworms, but they don’t realize how ignorant their clients are about heartworms,” Dr. Carithers said. “And they aren’t taking the time to go ahead and explain how heartworm disease is transmitted.”

Dr. Carithers said the survey also shows overall declines in infections in the West, which he attributes to effects of drought on mosquito populations.

The AHS conducts surveys on heartworm testing results every three years. About 6,000 veterinary practices and animal shelters provided data for the 2019 survey.

AHS officials said survey results show a gradual rise in the number of U.S. dogs with heartworm disease—about 12% since the organization’s first survey 18 years earlier. Using the survey results and national dog population figures, they estimate the U.S. had about 890,000 dogs positive for heartworm in 2001 and 1 million in 2019.

Mississippi had the highest heartworm incidence in the 2019 survey, with positive tests for heartworms in almost 10% of dogs, AHS data show. The next nine highest-incidence states also are in the South: Louisiana, South Carolina, Arkansas, Alabama, Texas, Tennessee, Georgia, North Carolina, and Oklahoma.

Dr. Carithers said the AHS data show a need to teach pet owners about heartworm prevention and how to protect their animals.

At his practice along the Gulf Coast of Mississippi, Dr. Duke uses AHS incidence maps to teach clients about the high volume of positive reports in the region and convince them to buy heartworm preventives. He said the maps show the battle veterinarians and their clients face in trying to keep dogs healthy.

Dr. Duke recommends giving clients the same messages about heartworm, from the first visit with a puppy to the annual checkups with a senior dog.

“If you don’t ask those basic questions every time they’re in your clinic for a preventive health talk, you’re missing the boat, and you’re not doing your job,” he said.

Eradicating heartworm is impossible in Dr. Duke’s region of Mississippi because of the combination of warm temperatures, standing water, and wild animals, including coyotes and wolves.

“We can’t kill every mosquito, but we can protect every dog,” Dr. Duke said.

The AHS publishes resources for veterinarians, including maps and guidelines on heartworm prevention, diagnosis, and management.

Correction: A previous version of this article misattributed a statement to Dr. Chris Duke, president of the American Heartworm Society.