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Lyme disease remains remarkably poorly understood in horses. Because of this, experts on the infectious disease recently convened to help clear up some misconceptions*.

Lyme disease, most commonly caused by the bacterium Borrelia burgdorferi, transfers between certain tick species and horses as the tick obtains a blood meal. Once transferred, the actual voyage of the bacterium through the horse’s body remains unclear,” explained Laura Petroski, B.V.M.S., a veterinarian at Kentucky Equine Research.

Considering the controversy associated with Lyme disease, the American College of Veterinary Internal Medicine recruited a panel of experts to thoroughly review all of the available data on Lyme disease in horses. Those experts subsequently assessed the strength of the available data to make clear recommendations regarding diagnosis, treatment, and prevention.

The most important recommendations made by the panel of experts included the following:

  • The geographical range of B. burgdorferi in the United States has increased, placing more and more horses at risk of infection.
  • Several blood tests can be used to test for Lyme disease. In healthy horses, a positive test result indicates past or current exposure to B. burgdorferi. A positive test does not predict whether a healthy horse will develop clinical signs of the disease.
  • In healthy horses residing in areas that harbor B. burgdorferi populations, Lyme disease tests will likely be positive, but this does not predict the chances of disease development.
  • The most common tissues affected by B. burgdorferi infection in horses include the nervous, ocular, and skin.
  • Many diseases share similar clinical signs with Lyme disease.
  • Lyme disease is likely overdiagnosed in geographical regions where horses are commonly exposed to ticks, like the northeastern United States.
  • Ruling out other diseases that could be responsible for the horse’s clinical signs rather than relying on response to treatment for Lyme disease is strongly recommended.
  • Do not treat horses solely based on a positive blood test.
  • If treatment is pursued, tetracycline and other beta-lactam antibiotics should be considered.
  • Little evidence exists to guide treatment duration. Current data suggest that duration of treatment should be based on clinical response and declining antibody levels in the bloodstream.
  • Unnecessarily treating horses that show no signs of disease and that are simply positive for a B. burgdorferi test is an unnecessary expense, may cause potential adverse reactions, and is an inappropriate use of antimicrobial drugs.

“As with other infectious diseases, not all horses exposed to the B. burgdorferi will develop Lyme disease. A horse’s immune system naturally fights off many infections,” reminded Petroski.

For maximal health of the immune system, ensure your horse has a balanced diet. This is especially important for young and old horses, those in heavy training, and horses exposed to stressful situations.

“To ensure your horse’s diet is appropriately formulated and supplemented with the appropriate products, consult with a Kentucky Equine Research nutrition advisor today,” advised Petroski.

*Divers, T.J., R.B. Gardner, J.E. Madigan, et al. Borrelia burgdorferi infection and Lyme disease in North American horses: A consensus statement. Journal of Veterinary Internal Medicine. In press.

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