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A multicenter case-control study of risk factors for equine protozoal myeloencephalitis

Noah D. Cohen VMD, MPH, PhD, DACVIM1, Robert J. MacKay BVSc, PhD, DACVIM2, Ellen Toby PhD3, Frank M. Andrews DVM, MS, DACVIM4, Bonnie S. Barr VMD, DACVIM5, Jill Beech VMD, DACVIM6, William V. Bernard DVM, DACVIM7, Carol K. Clark DVM, MS, DACVIM8, Thomas J. Divers DVM, DACVIM, DACVECC9, Martin O. Furr DVM, PhD, DACVIM10, Catherine W. Kohn VMD, DACVIM11, Michel Levy DVM, DACVIM12, Stephen M. Reed DVM, DACVIM13, Thomas L. Seahorn DVM, MS, DACVIM, DACVECC14, and Nathan M. Slovis DVM, DACVIM15
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  • 1 Department of Large Animal Clinical Sciences, College of Science, Texas A&M University, College Station, TX 77843-4475.
  • | 2 Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 100136.
  • | 3 College of Veterinary Medicine, and Department of Statistics, College of Science, Texas A&M University, College Station, TX 77843-4475.
  • | 4 Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996.
  • | 5 Rood & Riddle Equine Hospital, PO Box 12070, Lexington, KY 40580.
  • | 6 Department of Clinical Sciences, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 7 Rood & Riddle Equine Hospital, PO Box 12070, Lexington, KY 40580.
  • | 8 Peterson & Smith Equine Hospital, 4747 SW 60th Ave, Ocala, FL 34474.
  • | 9 Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.
  • | 10 Marion duPont Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Leesburg, VA 22075.
  • | 11 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.
  • | 12 Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.
  • | 13 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.
  • | 14 McGee Medicine Center, Hagyard Equine Medical Institute, 4250 Iron Works Pike, Lexington, KY 40511.
  • | 15 McGee Medicine Center, Hagyard Equine Medical Institute, 4250 Iron Works Pike, Lexington, KY 40511.

Abstract

Objective—To identify risk factors for equine protozoal myeloencephalitis (EPM) among horses examined at 11 equine referral hospitals.

Design—Case-control study.

Animals—183 horses with EPM, 297 horses with neurologic disease other than EPM (neurologic controls), and 168 horses with non-neurologic diseases (non-neurologic controls) examined at 11 equine referral hospitals in the United States.

Procedures—A study data form was completed for all horses. Data were compared between the case group and each of the control groups by means of bivariate and multivariate polytomous logistic regression.

Results—Relative to neurologic control horses, case horses were more likely to be ≥ 2 years old and to have a history of cats residing on the premises. Relative to non-neurologic control horses, case horses were more likely to be used for racing or Western performance.

Conclusions and Clinical Relevance—Results indicated that cats may play a role in the natural epidemiology of EPM, that the disease is less common among horses < 2 years of age relative to other neurologic diseases, and that horses used for particular types of competition may have an increased risk of developing EPM.

Abstract

Objective—To identify risk factors for equine protozoal myeloencephalitis (EPM) among horses examined at 11 equine referral hospitals.

Design—Case-control study.

Animals—183 horses with EPM, 297 horses with neurologic disease other than EPM (neurologic controls), and 168 horses with non-neurologic diseases (non-neurologic controls) examined at 11 equine referral hospitals in the United States.

Procedures—A study data form was completed for all horses. Data were compared between the case group and each of the control groups by means of bivariate and multivariate polytomous logistic regression.

Results—Relative to neurologic control horses, case horses were more likely to be ≥ 2 years old and to have a history of cats residing on the premises. Relative to non-neurologic control horses, case horses were more likely to be used for racing or Western performance.

Conclusions and Clinical Relevance—Results indicated that cats may play a role in the natural epidemiology of EPM, that the disease is less common among horses < 2 years of age relative to other neurologic diseases, and that horses used for particular types of competition may have an increased risk of developing EPM.

Contributor Notes

Dr. Bernard's present address is 4901 Mt Horeb Pike, Lexington, KY 40511. Dr. Reed's present address is Rood & Riddle Equine Hospital, PO Box 12070, Lexington, KY 40511. Dr. Seahorn's present address is 629 Craig Ln, Georgetown, KY 40324.

Supported by Fort Dodge Animal Health, with supplemental support from the Link Equine Research Fund, Texas A&M University.

The authors thank Ms. Heather Quiram and Ms. Lindsay German for technical assistance.

Address correspondence to Dr. Cohen.