Animal Health Diagnostic Center

Lyme disease is induced by the spirochete B. burgdorferi. Spirochetes are transmitted to horses by infected ticks. Similar to humans, horses are incidental, dead-end hosts for B. burgdorferi 1. Not all infected horses develop clinical signs of Lyme disease. If clinical signs occur, they can include chronic weight loss, sporadic lameness, shifting leg lameness, low-grade fever, muscle tenderness, chronically poor performance, swollen joints, arthritis and diverse orthopedic problems 2-5. Changes in behavior and skin sensitivity (tactile hyper-aesthesia), both with rapid onset, are common clinical signs seen by many practitioners in horses with potential Lyme disease. Neurological signs such as depression, dysphagia, head tilt and encephalitis were reported in chronic cases 2,6,7. Most recent reports describe horses with a Borreliaassociated pseudolymphoma 8 or Borrelia-associated uveitis 9.