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Incidence of Equine Protozoal Myeloencephalitis (EPM) in Veterinary Teaching Hospitals
Journal of Equine Veterinary Science (2016)
  • F.M. Andrews
  • Agricola Odoi
  • C.S. Sommardahl
Equine Protozoal Myeloencephalitis (EPM) is a serious neurologic disease in equids. Although seroprevalence has been reported to be high in horses, the actual prevalence of disease has been estimated between 0.5 to 1%, based on laboratory submission to the University of Kentucky. However, incidence (number of new diagnosed cases) of EPM in horses has not been reported. The purpose of this study was to determine the incidence and breed of EPM cases in equids presented to Veterinary Teaching Hospitals (VTH) in North America and to determine if the incidence of EPM was decreasing over time. A secondary purpose of the study was to survey veterinary practitioners to determine if they perceive that the incidence of EPM is decreasing over time. Equine accessions reported to the Veterinary Medical Data Base (VMDB) from 1990-2014 were used for this study. Medical records from the VMDB (Systematized Nomenclature of Medicine [SNOMED] and Systematized Nomenclature of Veterinary Diseases and Operations [SNVDO]) were accessed for overall EPM proportional morbidity rates (PMR), PMR by database, PMR compared by breed, and annual PMR from 1990-2014. Also, results of an on-line survey questionnaire ( were summarized. The on-line survey, containing 12 questions, was completed by equine practitioners who were members of either the Equine Clinicians Network (ECN) or the American Association of Equine Practitioners (AAEP) list-serves. There were 2,748 cases of EPM per 312,222 accessions resulting in an overall PMR of 0.88%, among hospitals reporting to the VMDB during the study period. The PMR was not significantly different between the two databases (SNOMED and SNOVDO). Proportional diagnoses increased from 0.293% in 1990 to 1.952% in 1997, which was a significantly (P<0.05) higher than the overall PMR (0.88%). Although, there was a significant increase in the PMR of EPM cases from 1995-1998, there was no evidence of a significant temporal increase over the 24-year study period. The PMRs were significantly (P<0.05) higher in Standardbreds (1.592%), Walking Horses (1.367%), Thoroughbreds (1.314%), and Warmbloods (1.096%) than all breeds combined (0.88%). However, the PMRs were significantly (P<0.05) lower in Draft breeds (0.518%), Ponies (0.591%), and Quarter Horses (0.694%), when compared to the PMR for all breeds. For the survey, there were 221 respondents and 153 (69%) were from private practice and 68 (31%) were from academia. The average number of practitioners per practice was 8. Thirty-eight percent of the equine practitioners perceived that it had not changed over the previous 2-4 years. Our findings seem to suggest breed predispositions, with higher PMRs being observed in Standardbreds, Walking Horses, and Thoroughbreds and lower PMRs being observed in Draft breeds, ponies and Quarter Horses. The majority of practitioners surveyed thought that the incidence of EPM had either not changed or decreased in the previous 2-4 years. Although there was a significant increase in EPM case diagnosed from 1995-1997, it appears from these data that the overall proportion of EPM cases has essentially not changed over the past 24 years.
Publication Date
April, 2016
Citation Information
F.M. Andrews, Agricola Odoi and C.S. Sommardahl. "Incidence of Equine Protozoal Myeloencephalitis (EPM) in Veterinary Teaching Hospitals" Journal of Equine Veterinary Science Vol. 39 (2016) p. S28
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