Annual CAPC pet parasite forecast predicts continuing spread across US

The four vector-borne diseases the Companion Animal Parasite Council (CAPC) tracks annually—anaplasmosis, ehrlichiosis, heartworm, and Lyme—continue to spread across the U.S.

The council has been forecasting the four parasitic diseases since 2012 with over 94% accuracy to help veterinarians assess related risks in their communities.

“These forecasts provide critical insights for both pet and public health, as pets and their owners live and play in the same places,” said Dr. Brian Herrin, CAPC board president, in an April 14 press release. “It’s also important to remember that low risk doesn’t mean no risk, so year-round prevention is essential to keeping pets safe from these potentially fatal diseases.”

The 2025 CAPC Annual Pet Parasite Forecasts, based on over 10 million reported diagnostic tests, show the prevalence of pet and human vector-borne diseases continues to expand geographically nationwide, largely because of shifting tick and mosquito populations.

Lyme disease

The geographic range of the Lyme disease tick vector (Ixodes scapularis) continues to grow, with populations from the North seeming to pose a greater risk for transmitting Lyme disease. The report also notes tick populations are not only spreading south and west, but also into new areas of Canada.

“This highlights the complexity of tick-transmitted diseases and their interaction with the environment,” the report states, adding that spread is not simply tied to warmer temperatures.

The Upper Midwest and Northeast continue to be high-risk areas for Lyme disease, while also becoming increasingly connected amid growing risk across Illinois, Indiana, Michigan, and Ohio. In addition, Lyme-disease risk is spreading into northern North Carolina and eastern Tennessee on a southward trajectory.

Heartworm disease

The forecast predicts the highest risk of heartworm infection in the Southeast with a consistent creep northward along the Mississippi river, as well as the Atlantic coast.

There has not been a significant northward expansion into the Upper Midwest or the Northeast; however, the council warns animal transports from the South to big cities in the North pose “a real threat,” urging veterinarians in those areas to still be on guard for heartworm.

In addition, veterinarians in areas not considered to be endemic for heartworm—Colorado, Montana, New Mexico, North Dakota, and Wyoming—are diagnosing heartworm disease “at a higher-than-expected rate,” indicating a need for routine testing for all dogs.

Ehrlichiosis, anaplasmosis

Regarding ehrlichiosis, the forecast predicts increasing numbers of seropositive dogs in western states, compared with 2024.

Notably, the Southwest is expected to see an increase in Ehrlichia- and Anaplasma-infected ticks, which transmit Rickettsia rickettsii, the causative agent of Rocky Mountain Spotted Fever (RMSF).

“This is significant in itself as Ehrlichia canis and Anaplasma platys themselves are highly pathogenic, even fatal, to dogs,” Dr. Herrin told AVMA News. “When you include the fact that the brown dog tick is an indoor tick and can spread RMSF to dogs and humans, that level of concern goes up drastically.”

Also, as the lone star stick continues its northward expansion, it carries a higher risk of ehrlichiosis into Upper Midwest states that have historically been nonendemic, and the New England region.

CAPC advises veterinarians to remain proactive about pet parasite prevention protocols, regardless of whether they are in an area traditionally considered endemic.

“These diseases and our society are dynamic,” Dr. Herrin said. “CAPC encourages veterinarians to stay alert and aware of the changing nature of these diseases in their areas.”