Lyme Disease is considered the most important insect-borne bacterial infection in North America. It is spread to mammals via the bite of specific hard-bodied ticks. The most common clinical signs observed in horses infected with Lyme disease are lameness involving multiple joints (75%) and behavioral changes (50%). “Shifting lameness” is the most common presenting clinical sign, with a variety of other manifestations also reported. Affected horses are in obvious discomfort and frequently unable to work. A diagnosis is difficult because of the many causes of equine lameness and the high incidence of sub-clinical infection in the equine population in endemic regions. A clinical diagnosis generally involves a physical examination, including functional and radiographic testing to rule out other causes of lameness, supportive serology testing, and response to treatment.
There is no vaccine approved for use in horses, but the vaccine marketed for dogs has been shown to be safe when used on horses. Veterinary researchers at Cornell University performed studies with an experimental vaccine that showed effectiveness in preventing disease in horses. Their study protocol is most closely imitated by the administration of three 1 ml doses of dog vaccine. The vaccine is administered alone (without other vaccines against other diseases at the same time), the second dose three weeks after the first, and the third dose three months after the first. We will administer the vaccine at the owner’s request, but it should be noted that this vaccine is not licensed for use in horses. The first year, three doses are required, followed by boosters every six months. Recent studies have shown that antibody titers from vaccination begin to decrease after six months, so boosters every six months are needed to maintain adequate levels of protection.