Most of the horses were ataxic (lack of muscle coordination) and showed cranial nerve deficits such as difficulty eating and breathing, tremors of the muzzle, and poor tongue tone. | Photo: iStock

Most horses in the Mid-Atlantic region show evidence of exposure to Borrelia burgdorferi, the bacterium that causes Lyme disease. The majority of exposed horses do not develop clinical signs of disease. However, a small number of infected horses will develop disease of the nervous system, termed Lyme neuroborreliosis.

Diagnosis of equine Lyme neuroborreliosis is often elusive and the disease provokes more questions than answers: What signs do horses with Lyme disease show? What test can be used to diagnose the disease? How should test results be interpreted?

Recently veterinarians from the University of Pennsylvania School of Veterinary Medicine’s New Bolton Center, led by Laura Johnstone, BVSc, MVSc, Dipl. ACVIM, a resident in Internal Medicine, sought to answer some of these questions by reviewing the medical records of horses that had histologic findings consistent with previous reports of Lyme neuroborreliosis in both horses and humans. Amy Johnson, DVM, Dipl. ACVIM, an assistant professor of large animal internal medicine and neurology, also participated in the research