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Viruses2024; 16(12); doi: 10.3390/v16121963

Investigation of an Outbreak of Equine Herpesvirus-1 Myeloencephalopathy in a Population of Aged Working Equids.

Abstract: The objective of this study was to describe an outbreak of equine herpesvirus-1 myeloencephalopathy (EHM) in a population of aged equids. The outbreak was linked to the introduction of five healthy non-resident horses 15 days prior to the first case of acute recumbency. This fulminant EHM outbreak was predisposed by the grouping of the 33 unvaccinated animals in two large pens with shared water and feed troughs. Fourteen horses (42.4%) developed neurological deficits within the first week of the outbreak. Four additional equids developed fever and respiratory signs (EHV-1 infection), while fifteen horses remained healthy. EHM was supported by the detection of EHV-1 N752 in blood (n = 11) and/or nasal secretions (9). Three out of four equids with EHV-1 infection and two out of fifteen healthy horses tested qPCR-positive for EHV-1. All animals were managed in the field. EHM and EHV-1 equids were treated with a combination of antiherpetic, anti-inflammatory, and antithrombotic drugs. Six out of fourteen EHM horses (42.9%) were euthanized because of recumbence and the inability to stand with assistance or vestibular signs. Anti-EHV-1 total IgG and IgG 4/7 levels in acute serum samples showed no significant difference amongst the three disease groups (p > 0.05); however, antibody levels rose significantly between acute and convalescent serum samples for EHM (p = 0.0001) and EHV-1 equids (p = 0.02). This outbreak highlights a very high EHM attack and fatality rate in a population of aged equids and rapid spread of EHV-1, as the population shared common pens and feeding practices. The outbreak also showed that EHM cases can be managed in the field when referral to a hospital is not an option.
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Publication Date: 2024-12-21 PubMed ID: 39772269PubMed Central: PMC11728824DOI: 10.3390/v16121963Google Scholar: Lookup
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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.

This study investigates an outbreak of the equine herpesvirus-1 myeloencephalopathy (EHM) disease in a group of aged horses and its link to the introduction of new horses and common living conditions. The research discusses the treatment used and the response in terms of antibodies, noting that the disease can be managed on-site when hospital referral is not possible.

Context and Objective of the Study

  • The study was aimed at investigating an outbreak of EHM, a neurologic disease caused by equine herpesvirus-1 (EHV-1), in a group of aged horses.
  • The outbreak happened after the introduction of five new horses, and it quickly spread amongst the horses that were grouped in two pens, consuming water and food from shared troughs.

Outbreak and Symptomatic Observation

  • The outbreak was severe and swift; 42.4% of the horses showed neurological deficits within the first week.
  • Along with EHM, four additional horses showed symptoms of fever and respiratory signs indicative of EHV-1 infection, while fifteen horses did not exhibit any symptoms.
  • EHM was confirmed with the detection of EHV-1 N in the blood and nasal secretions of the affected horses.

Management and Treatment

  • All horses were managed onsite, with EHM and EHV-1 positive horses given a combination of antiherpetic, anti-inflammatory, and antithrombotic drugs.
  • Of the horses that developed EHM, around 42.9% had to be euthanized due to severe symptoms, such as recumbency (inability to get up) and extreme vestibular signs (indicative of a problem with balance).

Impact on Immunity: Antibody Levels

  • The acute serum samples showed no significant difference in the Anti-EHV-1 total IgG and IgG 4/7 levels among the three disease groups. This means that the initial immune response did not vary significantly between the different groups of horses.
  • However, when compared to the convalescent serum samples, a significant increase in antibody levels was observed for EHM and EHV-1 affected horses. This shows the body’s increased immune response to the EHV-1 infection over time.

Final Observations

  • The study emphasizes the rapidity of EHM outbreak and the high fatality rate in an aged population of horses, especially under shared penning and feeding conditions.
  • The research also suggests that with appropriate treatment, EHM cases can be effectively managed on the field without the need for hospital referral.

Cite This Article

APA
Pusterla N, Lawton K, Barnum S, Ross K, Purcell K. (2024). Investigation of an Outbreak of Equine Herpesvirus-1 Myeloencephalopathy in a Population of Aged Working Equids. Viruses, 16(12). https://doi.org/10.3390/v16121963

Publication

Viruses
ISSN: 1999-4915
NlmUniqueID: 101509722
Country: Switzerland
Language: English
Volume: 16
Issue: 12

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.
Ross, Kelly
  • Camp Richardson Corral, South Lake Tahoe, CA 96150, USA.
Purcell, Kris
  • Carson Valley Large Animal Clinic, Gardnerville, NV 89460, USA.

MeSH Terms

  • Animals
  • Antibodies, Viral / blood
  • Disease Outbreaks / veterinary
  • Herpesviridae Infections / veterinary
  • Herpesviridae Infections / epidemiology
  • Herpesviridae Infections / virology
  • Herpesvirus 1, Equid / isolation & purification
  • Herpesvirus 1, Equid / genetics
  • Horse Diseases / virology
  • Horse Diseases / epidemiology
  • Horses / virology

Conflict of Interest Statement

The authors declare no conflicts of interest.

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Citations

This article has been cited 4 times.
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  2. ElShamey E, Yang J, Yang X, Hasan MM, Yang T, Zeng Y. Genetic Divergence and Functional Significance of Bioactive Compounds in Rice and Barley: Implications for Biofortification and Human Health. Int J Mol Sci 2025 Jul 30;26(15).
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  3. Musoles-Cuenca B, Padilla-Blanco M, Vitale V, Lorenzo-Bermejo T, de la Cuesta-Torrado M, Ballester B, Maiques E, Rubio-Guerri C, Velloso Alvarez A. First Molecular Evidence of Equine Herpesvirus Type 1 (EHV-1) in Ocular Swabs of Clinically Affected Horses. Viruses 2025 Jun 18;17(6).
    doi: 10.3390/v17060862pubmed: 40573453google scholar: lookup
  4. van Maanen K, van den Wollenberg L, de Haan T, Frippiat T. Epidemiology of Infectious Pathogens in Horses with Acute Respiratory Disease, Abortion, and Neurological Signs: Insights Gained from the Veterinary Surveillance System for Horses in The Netherlands (SEIN). Vet Sci 2025 Jun 10;12(6).
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