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Journal of veterinary internal medicine2025; 39(1); e17287; doi: 10.1111/jvim.17287

Comparison of clinical variables and outcome of 2 natural equine herpesvirus myeloencephalopathy outbreaks induced by equine herpesvirus-1 A2254/N752 strain in sport horses.

Abstract: Understanding of equine herpesvirus-1 (EHV-1) myeloencephalopathy (EHM) is complicated by disparities among studies. Objective: Compare clinical findings and outcome in horses involved in 2 recent EHM outbreaks. Methods: Twenty-five and 10 horses affected during 2 natural EHM outbreaks were admitted to a veterinary teaching hospital (VTH) in 2021 and 2023, respectively. Methods: Data collected from the VTH and surveys completed by riders and horse owners were analyzed retrospectively. Results: No risk factors associated with EHM development showed significant differences between the outbreaks; both outbreaks were caused by A2254/N752 strains. Treatments administered for EHM were not significantly different, whereas the duration was longer in 2021 for flunixin meglumine (P = .01) and dimethyl sulfoxide (P < .001). In 2021, more horses required hospitalization (P = .02), and fatality rate was 32%, whereas in 2023, no patient died. Hospitalization duration was longer in 2021 than in 2023 (P = .06) and 11.7% of horses from 2021 returned to competition within 6 months, whereas 100% in 2023 did (P < .001). Ataxia grade upon admission was equivalent in 2021 and 2023, but factors related to poor prognosis, such as simultaneous development of urinary and vascular complications, occurred in 2021 but not in 2023 (P = .01). Conclusions: Two EHM outbreaks caused by the A2254/N752 strain differed in disease severity. Urinary complications and systemic signs of vasculitis were important clinical variables associated with prognosis. Systemic complications in horses with EHM lead to a worse prognosis.
© 2025 The Author(s). Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.
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Publication Date: 2025-01-09 PubMed ID: 39778904PubMed Central: PMC11710857DOI: 10.1111/jvim.17287Google Scholar: Lookup
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  • Journal Article
  • Comparative Study

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This research compares clinical features and outcomes of two natural outbreaks of equine herpesvirus-1 myeloencephalopathy (EHM) in sport horses caused by the same viral strain.
  • The study identifies differences in disease severity and prognostic factors despite similarities in risk factors and treatment approaches.

Background

  • Equine herpesvirus-1 (EHV-1) can cause myeloencephalopathy (EHM), a serious neurological disease in horses.
  • Understanding EHM is challenging due to variations in clinical presentation and outcomes reported in different studies.
  • The specific EHV-1 strain studied was A2254/N752, known to cause EHM outbreaks.

Study Objective

  • To compare clinical findings, treatments, and outcomes of sport horses affected by two separate EHM outbreaks occurring in 2021 and 2023.
  • Assess differences in severity and factors influencing prognosis despite infections by the same viral strain.

Methods

  • Retrospective analysis of data from 25 horses affected in 2021 and 10 horses affected in 2023 admitted to a veterinary teaching hospital.
  • Data sources included hospital records and surveys completed by riders and owners.
  • Comparison focused on risk factors, treatments, hospitalization, clinical signs including ataxia and systemic complications, and outcomes such as mortality and return to competition.

Key Findings

  • Risk Factors and Strain:
    • No significant difference in risk factors for EHM between the two outbreaks.
    • Both outbreaks were caused by the same A2254/N752 strain of EHV-1.
  • Treatment:
    • Duration of some treatments (flunixin meglumine and dimethyl sulfoxide) was longer in the 2021 outbreak.
    • No significant difference in treatment types administered between outbreaks.
  • Hospitalization and Mortality:
    • More horses required hospitalization in 2021 than in 2023.
    • The fatality rate in 2021 was 32%; no deaths occurred in 2023.
    • Hospitalization tended to be longer in 2021 (~borderline significance).
  • Neurological Signs and Prognosis:
    • Ataxia severity on admission was similar in both outbreaks.
    • Complications associated with poor prognosis, such as urinary and vascular (vasculitis) issues, were present in 2021 but absent in 2023.
  • Return to Activity:
    • Only 11.7% of horses from 2021 returned to competition within 6 months versus 100% in 2023.

Interpretation and Conclusions

  • Despite the same EHV-1 strain and similar initial risk factors, the two outbreaks had markedly different clinical severities and outcomes.
  • Systemic complications, such as urinary problems and vasculitis, were important negative prognostic indicators.
  • Horses without these systemic signs had better survival and recovery rates, emphasizing the role of systemic involvement in EHM severity.
  • This study highlights that factors beyond viral strain alone influence disease outcome, possibly including host factors or management differences during outbreaks.
  • Findings can help veterinarians better predict prognosis and guide treatment strategies during EHV-1 outbreaks.

Cite This Article

APA
de la Cuesta-Torrado M, Velloso Alvarez A, Cárdenas-Rebollo JM, Neira-Egea P, Vitale V, Cuervo-Arango J. (2025). Comparison of clinical variables and outcome of 2 natural equine herpesvirus myeloencephalopathy outbreaks induced by equine herpesvirus-1 A2254/N752 strain in sport horses. J Vet Intern Med, 39(1), e17287. https://doi.org/10.1111/jvim.17287

Publication

Journal of veterinary internal medicine
ISSN: 1939-1676
NlmUniqueID: 8708660
Country: United States
Language: English
Volume: 39
Issue: 1
Pages: e17287
PII: e17287

Researcher Affiliations

de la Cuesta-Torrado, María
  • Department Animal Medicine and Surgery, Universidad CEU-Cardenal Herrera, CEU Universities, Alfara del Patriarca, Valencia, Spain.
  • Veterinary Teaching Hospital, Universidad Cardenal Herrera CEU, Alfara del Patriarca, Valencia, Spain.
Velloso Alvarez, Ana
  • Department Animal Medicine and Surgery, Universidad CEU-Cardenal Herrera, CEU Universities, Alfara del Patriarca, Valencia, Spain.
  • Veterinary Teaching Hospital, Universidad Cardenal Herrera CEU, Alfara del Patriarca, Valencia, Spain.
Cárdenas-Rebollo, José Miguel
  • Department of Mathematics and Data Science, Faculty of Economic and Business Sciences, Universidad San Pablo-CEU, CEU Universities, Madrid, Spain.
Neira-Egea, Patricia
  • Veterinary Teaching Hospital, Universidad Cardenal Herrera CEU, Alfara del Patriarca, Valencia, Spain.
Vitale, Valentina
  • Department Animal Medicine and Surgery, Universidad CEU-Cardenal Herrera, CEU Universities, Alfara del Patriarca, Valencia, Spain.
  • Veterinary Teaching Hospital, Universidad Cardenal Herrera CEU, Alfara del Patriarca, Valencia, Spain.
Cuervo-Arango, Juan
  • Department Animal Medicine and Surgery, Universidad CEU-Cardenal Herrera, CEU Universities, Alfara del Patriarca, Valencia, Spain.
  • Veterinary Teaching Hospital, Universidad Cardenal Herrera CEU, Alfara del Patriarca, Valencia, Spain.

MeSH Terms

  • Animals
  • Horses
  • Horse Diseases / virology
  • Horse Diseases / epidemiology
  • Herpesvirus 1, Equid
  • Herpesviridae Infections / veterinary
  • Herpesviridae Infections / epidemiology
  • Herpesviridae Infections / virology
  • Disease Outbreaks / veterinary
  • Retrospective Studies
  • Male
  • Female
  • Clonixin / analogs & derivatives
  • Clonixin / therapeutic use
  • Encephalomyelitis / veterinary
  • Encephalomyelitis / virology
  • Dimethyl Sulfoxide / therapeutic use

Grant Funding

  • Fundación Universitaria San Pablo CEU
  • GIR23-33 / Universidad Cardenal Herrera-CEU

Conflict of Interest Statement

Authors declare no conflict of interest.

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Citations

This article has been cited 1 times.
  1. de la Cuesta-Torrado M, Vitale V, Velloso Alvarez A, Neira-Egea P, Diss C, Cuervo-Arango J. The Effect of Vaccination Status on Total Lymphocyte Count in Horses Affected by Equine Herpes Virus-1 Myeloencephalopathy. Animals (Basel) 2025 Apr 1;15(7).
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