CAPC forecasts continuing spread of parasitic diseases

The pathogens that cause heartworm disease, Lyme disease, ehrlichiosis, and anaplasmosis continue to increase and spread throughout the U.S.

Mosquito-borne and tick-borne human disease incidence in the United States tripled between 2004 and 2016, according to the Centers for Disease Control and Prevention (CDC), with much of this increase due to tick-borne pathogens that were reported in higher numbers and across a larger geographic area.

New vectors, such as the Asian long-horned tick, continue to expand their geographic range in the U.S. and their full pathogen transmission potential is still unknown.

A heat map of the United States shows the forecasted prevalence of Lyme Disease in 2024
The Companion Animal Parasite Council (CAPC) recommends veterinarians in regions of high prevalence and forecasted areas of increased risk for Lyme disease and other tick-borne pathogens should reinforce their recommendations of aggressive tick control. (Images courtesy of CAPC)

That’s according to the Companion Animal Parasite Council’s (CAPC) 2024 Pet Parasite Forecasts, released on April 17, which highlight areas of risk for companion animals as these diseases grow.

A high risk of heartworm infection continues along the Mississippi River, throughout southern portions of the Midwest, and along the Atlantic coast into Virginia and southern New Jersey.

The incidence of heartworm continues to increase in the mid-Atlantic region, pushing northward into the densely populated regions of the northeast, according to the forecast.

Additional areas likely to experience increased risk include New Mexico, portions of Colorado, and the northern Great Plains.

“While heartworm is still prevalent in much of the southeastern U.S., we are seeing an increased likelihood of heartworm infection in parts of North and South Dakota and Montana,” said Heather Walden, PhD, president of the CAPC board.

A heat map of the United States shows the forecasted prevalence of heartworm in 2024

The blacklegged or deer tick Ixodes scapularis is a vector for a number of pathogens and is the primary carrier of the bacterium Borrelia burgdorferi responsible for causing Lyme disease in humans as well as dogs, horses, and cats. This tick continues to expand its geographic range southward and westward outside of the historically high-risk areas such as the Northeast and Upper Midwest.

High-risk hot spots for Lyme disease are again predicted in northern and southwestern Michigan and southern Indiana.

A higher-than-normal risk is expected to continue in North Dakota, northeastern South Dakota, southeastern Iowa, Illinois, and eastern Kentucky. For the first time, Lyme forecasts include eastern Montana.

The high prevalence areas for ehrlichiosis are more widespread and less well-defined than other vector-borne pathogens.

The forecasted risks of Ehrlichia spp. in dogs remain high throughout the Southeast, Southwest, South Central, and coastal Atlantic states. Risks also continue in much of Colorado and many parts of Wyoming.

“We are also seeing new species of Ehrlichia in parts of Wisconsin and Minnesota, so testing is essential to help minimize transmission and disease,” said Walden, who is associate professor of parasitology at the University of Florida College of Veterinary Medicine.

Exposure to Anaplasma-infected ticks is expected tocontinuein the Northeast and Upper Midwest. Forecasts predict an increase in eastern Kentucky, eastern Tennessee, and northwestern North Carolina. An increased prevalence is also forecasted in western North Dakota and eastern Montana.

To develop the 2024 Pet Parasite Forecast, leading parasitologists collaborate with a team of statisticians to identify regions of the country that may experience higher parasite incidence. Many factors are analyzed, including the number of positive tests and the influence of weather patterns, vegetation indicators, and human population density.

“Knowing vector-borne disease risk in your home area, or if travel is planned, gives the veterinary professional and pet owner an idea of how to best protect the pet against vectors such as ticks and mosquitoes, along with the pathogens they transmit,” Walden said.

CAPC officials say the best preventive measures that veterinarians and their clients can take is to avoid contact between companion animals and these vectors as well as use of year-round parasite prevention, including products that kill or repel ticks and mosquitoes.

To see full forecasts, maps, and other resources for veterinarians, visit the Companion Animal Parasite Council website.