Growing numbers of pets are at risk of contracting heartworm, Lyme, ehrlichiosis and anaplasmosis.

Pets can run, but they can’t hide from mosquitoes and ticks, the vectors for several preventable diseases.

The Companion Animal Parasite Council reported in its annual forecast that the risk of heartworm disease, Lyme disease and two other tick-borne illnesses is higher than usual in many areas of the United States in 2021. The nonprofit foundation, made up of parasitologists, veterinarians and other health experts, emphasized the need to test for common diseases and prescribe year-round preventive medications to keep pets healthy.

“Over the years, we’ve seen the risk for parasitic diseases continue to increase and expand into areas that have had historically lower prevalence,” said the organization’s CEO, Christopher Carpenter, DVM.

The CAPC’s 30-Day Pet Parasite Forecast Maps are posted at and updated monthly.

The current thinking is:

  • Heartworm disease: Higher than average risk along the Mississippi River, throughout southern portions of the Midwest, and along the Atlantic Coast north into Virginia and southern New Jersey. Increased risk in southern Arizona, Idaho, New Mexico, and Northern California, and portions of Colorado, Kansas, Montana, and North Dakota.
  • Lyme disease: Expanding south into the Carolinas and Tennessee. High-risk hot spots in northwestern and southwestern Michigan and southern and northeastern Ohio. High risk throughout the Northeast, Wisconsin, Minnesota, and Michigan’s Upper Peninsula. Higher than the normal risk in North Dakota, northern South Dakota, Iowa, southern Illinois, and western Kentucky.
  • Ehrlichiosis: Above-normal risk in New Mexico, Arizona, Southern California, northern Colorado, southern Wyoming, central and northeastern Illinois, and parts of Wisconsin and Minnesota.
  • Anaplasmosis: Increased risk in western regions of Pennsylvania and New York and Virginia, West Virginia, west and south Texas, and Northern California. High risk in Wisconsin, Minnesota and eastern North Dakota.

Mosquito-transmitted heartworm disease and tick-spread Lyme disease are found well beyond their traditional territories.

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