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Summary of the ACVIM Consensus Statement on Borrelia burgdorferi and Lyme disease in horses 

In February 2018, the American College of Veterinary Internal Medicine (ACVIM) released “Borrelia burgdorferi and Lyme Disease in North American Horses: A Consensus Statement”. This is the first consensus statement on the topic and a welcomed addition to the sparse literature on equine Lyme disease. 

Here are some of the highlights: 

  • Exposure to B. burgdorferi in horses is common in areas endemic for the tick vectors, I. scapularis or I. pacificus, and has been on the rise as these tick species undergo range expansion.

  • A variety of serological tests exist to assess antibodies to B. burgdorferi in horses. These tests need to be used cautiously because a positive test result: (1) only indicates exposure, (2) does not prove that any clinical signs the horses may be experiencing is due to B. burgdorferi infection, and (3) does not mean that the horses will experience disease in the future.  

  • Routine serological testing of healthy horses is generally not indicated. 

  • Lyme disease in horses can manifest as neuroborrelosis, uveitis and cutaneous pseudolymphoma. Limited evidence exists to support stiffness or lameness in horses as a result of B. burgdorferi infection, but we still do not understand the full range of clinical signs.

  • Diagnosis of clinical Lyme disease in horses can be challenging. Ruling out other diseases which present with similar symptoms should be undertaken. 

  • Treatment of equine Lyme disease can be challenging given the difficulty in making a diagnosis and the lack of oral bioavailability in horses for many antibiotics that are routinely used to treat Lyme disease in horses. 

  • Seropositive, but otherwise clinical healthy horses do not need to be treated.  


The authors also explore the immune response during infection, provide a summary of available tests, propose criteria for diagnosis of clinical cases, synthesize treatment guidelines, and discuss prevention and current controversies. We know that much research is still needed on B. burgdorferi infection in horses, but for any equine practitioner, this is certainly worth reading! 

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