An accurate diagnosis is key to implementing a successful treatment plan for any condition. But for many years, veterinarians were faced with subpar testing options when it came to diagnosing Lyme disease in horses. Recently, however, researchers have developed several new diagnostic options that are proving beneficial for diagnosing this tick-borne disease.
Bettina Wagner, DVM, Dr. med. vet. habil., reviewed equine Lyme disease and described diagnostic testing advancements at a lecture held at the University of Kentucky Maxwell H. Gluck Equine Research Center, in Lexington. Wagner is an associate professor of Immunology in the Cornell University College of Veterinary Medicine's Deptartment of Population Medicine and Diagnostic Sciences, and the Director of Serology at the Animal Health Diagnostic Center, in Ithaca, New York.
Lyme Disease 101
Wagner began with a brief review of Lyme disease, which is caused by the bacteria Borrelia burgdorferi and spread by Ixodes ticks. Horses, like humans and dogs, are incidental dead-end hosts. She estimated that 30% to 40% of affected horses develop chronic disease, but noted that epidemiologic data to confirm the chronic disease rate in horses are not yet available.
B. burgdorferi transmission from tick to horse takes 16 to 24 hours, Wagner explained, meaning a tick must be engorged in a horse for that time period in order to pass along the bacteria—just a fleeting bite won't do it. Clinical signs generally appear two to five months or more following disease transmission.
Clinical signs of Lyme disease are nonspecific in horses and include chronic weight loss, low-grade fever, sporadic or shifting leg lameness, muscle tenderness, and arthritis. Wagner said some horses also develop poor performance, high sensitivity to being touched, behavioral changes, or neurologic signs.
"Owners sometimes like to use this as an excuse for horses' bad behavior in endemic areas," Wagner said with a smile, but noted that Lyme-induced behavioral changes are typically sudden and significant (a horse going from quiet to untouchable in a day or so, for instance).
She also noted that researchers have recently identified Borrelia-associated pseudolymphoma (a benign disorder of lymphoid cells) and uveitis (inflammation of the eye's uvea).