Lyme disease, which is caused by the bacteria Borrelia burgdorferi and transmitted through the bite of a tick, affects domestic animals and humans. At least 3 known species of ticks can transmit Lyme disease. However, the great majority of Lyme disease transmissions are due to the bite of a very tiny tick commonly called the deer tick, or black-legged tick. The scientific name of the tick species involved is -Ixodes pacificus on the west coast of the US; -Ixodes scapularis is the species involved elsewhere. It is important to note that ticks do not cause Lyme disease; they merely harbor and transmit the bacteria that cause it.

Lyme disease occurs much more frequently in dogs than in other animals. Although horses have tested positive for exposure to the disease-causing bacteria, it is unclear whether there is a relationship between the exposure and any signs of infection such as lameness, fever, loss of appetite, fatigue, or difficulty breathing. It is best to consult with your veterinarian regarding the cause if any of these signs appear, particularly in areas where Lyme disease is common (including the northeastern and mid-Atlantic states in the United States). Antibiotics are required for treatment (see Disorders Affecting Multiple Body Systems of Dogs: Lyme Disease (Lyme Borreliosis) in Dogs).

The best protection against Lyme disease is to avoid exposing your horses to the ticks that transmit the Borrelia burgdorferi bacteria. Keep pastures mowed and remove areas where rodents nest. Ask your veterinarian to recommend an appropriate tick repellent for your horse. Daily grooming away from stalls or exercise areas can remove ticks resting on your horse's coat. If possible, capture and properly dispose of any ticks you find; otherwise they may reattach themselves to another horse or other animal. Remove any ticks by using fine-pointed tweezers to grasp the head of the tick (right where it enters the skin). Pull the tick straight off, making sure not to grasp or squeeze its body.

Last full review/revision July 2011 by Otto M. Radostits, CM, DVM, MSc, DACVIM (Deceased); Delores E. Hill, PhD; Barton W. Rohrbach, VMD, MPH, DACVPM; Charles J. Issel, DVM, PhD; Max J. Appel, DMV, PhD; David A. Ashford, DVM, MPH, DS; Daniela Bedenice, DrVetMed, DACVIM, DACVECC; Farouk M. Hamdy, DVM, MSc, PhD, MPA (Deceased); Kenneth R. Harkin, DVM, DACVIM; Johnny D. Hoskins, DVM, PhD; Eugene D. Janzen, DVM, MVS; Jodie Low Choy, BVMS; John E. Madigan, DVM, MS; Dale A. Moore, MS, DVM, MPVM, PhD; J. Glenn Songer, PhD; Joseph Taboada, DVM, DACVIM; Charles O. Thoen, DVM, PhD; John F. Timoney, MVB, PhD, Dsc, MRCVS; Ian Tizard, BVMS, PhD, DACVM; Brian J. McCluskey, DVM, MS, PhD, DACVPM; Bert E. Stromberg, PhD; Peter J. Timoney, MVB, MS, PhD, FRCVS