Heartworm incidence survey seeks veterinarian participation

The American Heartworm Society (AHS) is seeking insight from veterinarians about their understanding of heartworm disease in the US with a request to participate in the 2025 AHS Heartworm Incidence Survey. Using information collected from the survey, a heartworm incidence map will be created.1

These maps are widely used by veterinarians, animal shelters, pet owners about the threat of heartworm disease, according to AHS. The maps also provide insights for veterinary professionals about heartworm incidence trends and the spread of heartworms into new areas of the country.1

“Every veterinary practice that submits data helps the AHS to create a more comprehensive and useful map, which in turn helps veterinarians provide valuable information to clients on the threat of heartworms in their practice areas,” Marisa Ames, DVM, DACVIM (Cardiology), president of the AHS, said in a news release.1 Ames emphasized that neither size nor location of practice—nor the number of heartworm cases seen—should be a factor, adding that the brief survey can be completed online.

RELATED: Veterinary cardiologist named president of the American Heartworm Society

The AHS has generated maps every 3 years since 2001. The most recent release AHS map was released in April 2023, following a survey taken early the same year that collected information based on heartworm incidence in 2022.1,2

The deadline to submit survey data for the 2026 survey is February 14. “Whether yours is a large or small practice—or whether you live in a warm- or cold-weather state—we urge you to submit your information,” Ames said.1

The 2022 map showed an increase in heartworm prevalence in certain areas of the country. These areas include states in and adjacent to the lower Mississippi Delta that historically experiences a convergence of conditions fostering widespread heartworm infection. However, states with historically low heartworm rates also saw unexpected increases and the development of new “hot spot” areas in 2022 such as Washington, Oregon, Kansas, North Dakota, Massachusetts, and Connecticut. 2

In the 2023 survey, about 17% of the responding veterinarians reported drops in heartworm rates for 2022. The most common reasons cited for the drops were changes in pet owner behaviors that included an increase in heartworm preventives administered by pet owners—cited by 33% of the respondents reporting drops—and improvements on preventive compliance (31%).2

Michael W. Dryden, DVM, MS, PhD, DACVM (Parasitology), a professor (emeritus) at Kansas State University in Manhattan, Kansas, emphasized the need for parasiticides to be administered properly and consistently to prevent heartworm disease, during a keynote address at the 2025 Fetch dvm360 Conference in Kansas City, Missouri. Monthly parasiticide products are essentially “deworming” tools used to kill heartworm once in the subcutaneous stage (L3 and L4), according to Dryden. “They must be administered before L4 molt to the immature adult to be consistently effective,” he said.3

The FDA recommends prescription heartworm preventives approved by the agency as the best way to combat heartworm disease in dogs. The FDA has also approved injectable melarsomine dihydrochloride for killing adult heartworms in canines, and a topical combination of imidacloprid and moxidectin for ridding a dog’s bloodstream of microfilariae.4

Oral products administered monthly can kill L3 and L4 from up to 30 days prior with a short-term “pulse” of macrocyclic lactones anthelmintic activity that lasts a few days. Other products with different formulation of pharmacokinetics can also “reach back” 30 days. Injectable moxidectin is a slow-release formulation that provides an additional 6 to 12 months of protection, and transdermal moxidectin/imidacloprid features a slow dermal absorption and slow elimination from the blood, which allows it to achieve protection 30 days back and 30 days forward, according to Dryden.3

The AHS anticipates releasing the 2025 AHS map in April 2026., which is Heartworm Awareness Month. The new map will be available for public viewing.1

References

1. Numbers needed: Veterinarians urged to contribute clinic data for 2025 heartworm incidence map. News release. American Heartworm Society. December 29, 2025.
2. New heartworm incidence map shows increase in parasitic cases. dvm360. American Heartworm Society. April 20, 2023. Accessed January 6, 2026. https://www.dvm360.com/view/new-heartworm-incidence-map-shows-increase-in-parasitic-cases
3. Keep the worms out of your pet’s heart! The facts about heartworm disease. FDA. December 22, 2022. Accessed January 6, 2026. www.fda. gov/animal-veterinary/animal-health-literacykeep-worms-out-your-pets- heart-facts-about-heartworm-disease
4. Crossley KC. Breaking down how parasite preventives work. dvm360. August 24, 2025. Accessed January 6, 2026. https://www.dvm360.com/view/breaking-down-how-parasite-preventives-work