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Viruses2025; 17(5); doi: 10.3390/v17050608

Management of an Equine Herpesvirus-1 Outbreak During a Multi-Week Equestrian Event.

Abstract: The present study reports on the management of an EHV-1 outbreak at a large, multi-week equestrian event with ongoing showing. Within a 48 h period, 8 horses out of a cohort of 38 horses from the same trainer displayed elevated rectal temperatures ranging from 38.4 to 39.0 °C. Initial testing using a point-of-care PCR assay detected EHV-1 in 2/8 horses, with the results being confirmed at a later time by qPCR. As a precautionary measure and because of the inability to isolate the entire at-risk population, the 38 horses were relocated to an equine facility outside the equestrian event for daily monitoring and weekly EHV-1 qPCR testing of nasal secretions. Overall, 22/38 (58%) horses tested EHV-1 qPCR-positive in nasal secretions over the monitoring period of 28 days, with only one additional horse developing fever. Once all 38 horses tested EHV-1 qPCR-negative twice, 7 days apart, 17 horses returned to the equestrian event to compete for the remaining 2 weeks of the circuit. The present study highlights the importance of isolating and testing horses with fever but also subfebrile horses, as EHV-1 can cause silent infection. The relocation of the exposed horses to an outside facility allowed close monitoring of these horses while reducing the risk of direct and indirect exposure to other show horses. The regular testing for EHV-1 through nasal secretions during the outbreak, coupled with proper biosecurity protocols, allowed the safe return of the show horses to the event. The key elements in reducing the spread of EHV-1 were the routine assessment of rectal temperature, early isolation of horses with elevated rectal temperature and on-site EHV-1 PCR testing.
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Publication Date: 2025-04-24 PubMed ID: 40431620PubMed Central: PMC12116144DOI: 10.3390/v17050608Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't

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.

The research details how an outbreak of Equine Herpesvirus-1 (EHV-1) is managed during a multi-week equestrian event, highlighting that isolating and testing horses and regular maintenance of biosecurity protocols is crucial for preventing the spread of the virus.

Objective of the Research

  • The objective of this research was to record and scrutinize the management tactics in response to an EHV-1 breakout that took place in a large, multi-week equestrian event.

Outbreak Details and Initial Reaction

  • During the event, eight horses—out of a group of 38 horses undersame trainer—recorded elevated rectal temperatures within a 48 hour window. The temperatures ranged from 38.4 to 39.0°C, indicative of potential infection.
  • Initial testing using a point-of-care PCR assay identified EHV-1 in two of the eight symptomatic horses. These results were later confirmed via quantitative PCR testing (qPCR).
  • Due to the impossibility of isolating the entire group at risk, as a precaution, all 38 horses were moved to an external equine facility, separate from the equestrian event. This move was for daily monitoring and weekly EHV-1 qPCR testing via nasal secretions.

Monitoring and Test Results

  • Over a 28-day monitoring duration, EHV-1 was detected—via qPCR testing of nasal secretions—in 22 of the 38 horses (approximately 58%). Only one additional horse developed a fever.
  • The period of monitoring ended once all 38 horses tested negative for EHV-1 twice, with the tests conducted 7 days apart.
  • After these negative results, 17 horses returned to the equestrian event to compete for the remaining 2 weeks of the regulation.

Research Findings and Recommendations

  • The research enumerates the significance of isolating and testing horses not only with visible symptoms (fever) but also those with subfebrile conditions, as EHV-1 can cause a silent infection, i.e., an infection without noticeable symptoms.
  • The action of moving the potentially exposed horses to an off-site facility enabled detailed monitoring and reduced the risk of exposing other show horses, both direct and indirect, to the virus.
  • The adopted biosecurity protocols, with regular testing for EHV-1 through nasal secretions, facilitated the safe return of the horses to the event.
  • The research concluded the essential steps in limiting the spread of EHV-1 are: regular assessment of rectal temperature, promptly isolating horses with elevated rectal temperature, and conducting on-site EHV-1 PCR testing.

Cite This Article

APA
Pusterla N, Lawton K, Barnum S, Flynn K, Hankin S, Runk D, Mendonsa E, Doherty T. (2025). Management of an Equine Herpesvirus-1 Outbreak During a Multi-Week Equestrian Event. Viruses, 17(5). https://doi.org/10.3390/v17050608

Publication

Viruses
ISSN: 1999-4915
NlmUniqueID: 101509722
Country: Switzerland
Language: English
Volume: 17
Issue: 5

Researcher Affiliations

Pusterla, Nicola
  • Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Lawton, Kaila
  • Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Barnum, Samantha
  • Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Flynn, Katie
  • US Equestrian Federation, Lexington, KY 40511, USA.
Hankin, Steve
  • Desert International Horse Park, Thermal, CA 92274, USA.
Runk, David
  • Desert International Horse Park, Thermal, CA 92274, USA.
Mendonsa, Eric
  • Fluxergy, Irvine, CA 92618, USA.
Doherty, Tara
  • West Coast Equine Medicine, Temecula, CA 92590, USA.

MeSH Terms

  • Animals
  • Female
  • Male
  • Disease Outbreaks / veterinary
  • Herpesviridae Infections / veterinary
  • Herpesviridae Infections / epidemiology
  • Herpesviridae Infections / virology
  • Herpesviridae Infections / prevention & control
  • Herpesviridae Infections / diagnosis
  • Herpesvirus 1, Equid / isolation & purification
  • Herpesvirus 1, Equid / genetics
  • Horse Diseases / epidemiology
  • Horse Diseases / virology
  • Horse Diseases / prevention & control
  • Horse Diseases / diagnosis
  • Horses

Conflict of Interest Statement

N.P., K.L., S.B., K.F., S.H., D.R. and T.D. declare no conflict of interest. E.M. currently works for Fluxergy.

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