Are We Overdiagnosing Lyme Disease in Horses?

This article originally appeared in the Summer 2026 issue of EquiManagement. Sign up here for a FREE subscription to EquiManagement’s quarterly digital or print magazine and any special issues.

According to the American Association of Equine Practitioners’ (AAEP) 2025 publication Borrelia Burgdorferi Infection and Lyme Disease Guidelines, “Many horses infected with B. burgdorferi will remain asymptomatic and never develop clinical disease, and it is generally considered that infection is common, but clinical Lyme disease is rare.” And yet, equine practitioners like Jeanine Messak, DVM, associate veterinarian at Rood & Riddle Equine Hospital, in Saratoga, New York, and Lauren Holley, BVSc, DACVIM, internal medicine specialist at Rhinebeck Equine, also in New York, report that owners frequently believe their horses are showing signs of Lyme disease. Clinical signs owners attribute to Lyme disease predominantly include general malaise, stiffness, and lameness but might also include weight loss, low-grade fever, muscle tenderness, and poor performance.