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EQUINE LYME DISEASE

Lyme Disease is very complicated and limited research is available in horses to guide our decisions. Below is important information to consider prior to vaccinating your horse(s) for Lyme.

1) TESTING YOUR HORSE(S):

  • VLAC-EH recommends testing your horse for Lyme Disease prior to vaccination in order to have means of comparison should the horse develop the non-specific clinical signs of Lyme in the future.

2) THE LYME VACCINE:

  • The Lyme vaccine used in horses is a canine vaccine. There is no FDA approved Lyme vaccine for horses at this time. Limited research shows that horses do mount protective titers using the canine Lyme vaccine.

3) LYME DISEASE TESTING AND TITER INTERPRETATION:

  • The Lyme Multiplex Assay is run through the Animal Health Diagnostic Center at Cornell University and tests for 3 different Lyme antibody levels (titers), labeled OspA, OspC and OspF.
  • OspA positive status indicates vaccination. Studies have shown that after 5 months, the protective OspA antibodies produced by the Lyme vaccine declines, and therefore we recommend boostering every 6 months (spring and fall). Studies have shown that 5% of non-vaccinated horses can have a positive OspA titer. The biological role of OspA in these non-vaccinated horses is unknown.
  • OspC positive status indicates exposure to the Lyme organism of 2-3 weeks duration
  • OspF positive status indicates chronic exposure of at least 5 months duration
  • Previous exposure to Lyme resulting in high OspC and OspF titers has not been shown to protect against new infection.

4) TO TREAT OR NOT TO TREAT?

  • The available research does not indicate a specific protocol for responding to positive Lyme titers where no clinical signs are evident. For this reason the VLAC clinicians offer several ways to respond in this situation.
  • If the Lyme Multiplex Assay (Lyme titer) is positive in a horse with no apparent clinical signs, there are three options on how to proceed:
  •  Repeat titer in 4 weeks and monitor for development of clinical signs. If the titer is rising, then treatment may be warranted.
  • Monitor horse for clinical signs +/- vaccinate against new exposure to Lyme
  • Treat proactively prior to vaccination
  • The treatment for Lyme Disease in horses is tetracycline antibiotic. Many cases are treated with the oral antibiotic minocycline for 6 weeks. More severe cases may require starting with intravenous treatment with oxytetracycline (sometimes requiring hospitalization), followed by 6 weeks of oral Minocycline on the farm. Treatment is considered a success if the positive values are decreased by 50% on the post-treatment test.

5) TO VACCINATE OR NOT TO VACCINATE?

  • We recommend vaccination for Lyme Disease because we have no other method of prevention (aside from grooming and topical pesticides that are minimally effective). The initial series is 3 vaccinations, scheduled 1 month apart. The initial series should be followed every 6-12 months with a booster. Since research has shown the titer drops significantly after 5 months, vaccinating every 6 months is recommended for horses in high risk areas prone to ticks.

For more information on Lyme Disease in horses and the Lyme Multiplex assay, please follow the link below.
https://ahdc.vet.cornell.edu/docs/Lyme_Disease_Multiplex_Testing_for_Horses.pdf