Ticks can transmit a number of disease-causing organisms to horses, including Lyme disease. Lyme disease is caused by the bacterium Borrelia burgdorferi. Many horses are exposed to this organism through tick bites, but few develop clinical illness, usually months post tick bite.
As in dogs and people, the possible diagnosis of Lyme disease often arises when more common causes of lameness, joint swelling, kidney disease, moon blindness or incoordination have been ruled out.
Typically, two blood samples are taken 2 to 3 weeks apart to see if anti-Borrelia antibody levels have changed significantly to indicate active infection. The two samples are important because many normal horses may carry high antibody levels. The disease can also be diagnosed by finding the organism in tissue taken by biopsy from an affected joint or lymph node. The SNAP test kits utilized for testing dogs for Lyme disease are likely valid for use in the horse, but so far are not licensed for that purpose.
If evidence of Lyme disease is found, a veterinarian may try a course of antibiotics to see if this will improve the horse’s clinical abnormalities. There are currently no Lyme vaccines approved for use in the horse.
Horse owners need to be tick-vigilant and manage their horses’ environment to reduce tick habitat. Clearing brush out of pastures and along both sides of fence lines is recommended. Keeping pastures mowed may also be helpful. Before riding through long grass or brush, use of topical insecticides is highly recommended.
Author: Julia Wilson, DVM, MN Board of Veterinary Medicine.