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BMC veterinary research2024; 20(1); 287; doi: 10.1186/s12917-024-04149-x

Outbreak of equine herpesvirus 4 (EHV-4) in Denmark: tracing patient zero and viral characterization.

Abstract: Equine herpesvirus 4 (EHV-4) causes respiratory disease in horses, and the virus is considered endemic in the global equine population. However, outbreaks can occur when several horses are gathered in relation to shows, competitions, breeding units and at hospitals. In the spring year 2022, an EHV-4 outbreak occurred at the Large Animal Teaching Hospital, University of Copenhagen, Denmark. Nine horses were tested EHV-4 positive during the outbreak, which lasted approx. seven weeks. In addition, a tenth horse "Eq10" tested EHV-4 positive almost three weeks after the last of the outbreak horses tested positive. Detailed clinical registrations were obtained from all ten horses as well as their location and movement during hospitalization. Nasal swabs were obtained throughout the outbreak and tested by qPCR for EHV-4. Additionally, pre- and post-infection sera were tested for the presence of EHV-4 antibodies. Selected samples were characterized by partial and full genome sequencing. Results: The most common clinical signs of the EHV-4 infected horses during this outbreak were pyrexia, nasal discharge, mandibular lymphadenopathy and increased lung sounds upon auscultation. Based on the locations of the horses, EHV-4 detection and antibody responses the most likely "patient zero" was identified as being "Eq1". Partial genome sequencing revealed that Eq10 was infected by another wild type EHV-4 strain, suggesting that the hospital was able to eliminate the outbreak by testing and reinforcing biosecurity measures. The complete genome sequence of the outbreak strain was obtained and revealed a closer relation to Australian and Japanese EHV-4 strains rather than to other European EHV-4 strains, however, very limited sequence data are available from Europe. Conclusions: The study illustrated the transmission of EHV-4 within an equine facility/hospital and provided new insights into the viral shedding, antibody responses and clinical signs related to EHV-4 infections. Finally, sequencing proved a useful tool in understanding the transmission within the hospital, and in characterizing of the outbreak strain.
© 2024. The Author(s).
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Publication Date: 2024-07-03 PubMed ID: 38961400PubMed Central: PMC11221098DOI: 10.1186/s12917-024-04149-xGoogle Scholar: Lookup
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  • Journal Article

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 examines an outbreak of equine herpesvirus 4 (EHV-4) at a Danish veterinary hospital in 2022, identifying the initial infected horse and characterizing the virus through clinical, molecular, and genomic analyses.

Background and Context

  • EHV-4 is a virus that causes respiratory illness in horses worldwide and is commonly present (endemic) in horse populations.
  • Outbreaks typically occur when horses congregate in settings such as shows, breeding centers, competitions, and hospitals.
  • The study focuses on an outbreak at the Large Animal Teaching Hospital at the University of Copenhagen, Denmark, in spring 2022.

Outbreak Description and Sample Collection

  • The outbreak lasted approximately seven weeks and initially involved nine horses testing positive for EHV-4 via nasal swab qPCR testing.
  • A tenth horse (“Eq10”) tested positive about three weeks after the initial group’s last positive case, raising questions about ongoing transmission.
  • Clinical data were recorded for all ten horses, including symptoms and movement within the hospital.
  • Repeated nasal swab samples were taken during the outbreak to monitor viral presence and shedding using quantitative PCR.
  • Blood samples were collected before and after infection to measure antibody responses to EHV-4, providing insight into immunity development.

Clinical Findings

  • The infected horses commonly showed:
    • Pyrexia (fever)
    • Nasal discharge
    • Mandibular lymphadenopathy (swollen lymph nodes under the jaw)
    • Increased lung sounds on auscultation, indicating respiratory involvement
  • These symptoms are consistent with respiratory disease caused by EHV-4.

Tracing and Identification of Patient Zero

  • By correlating horse locations, timing of EHV-4 detection, and antibody responses, the researchers identified horse “Eq1” as the probable source of the outbreak (“patient zero”).

Viral Characterization and Whole Genome Sequencing

  • Partial genome sequencing of the virus from horse Eq10 revealed infection by a different EHV-4 strain compared to the outbreak strain affecting the initial nine horses.
  • This suggests that the hospital successfully contained the outbreak through testing and enhanced biosecurity measures, preventing the spread of the original virus strain.
  • The researchers sequenced the complete genome of the outbreak strain, revealing:
    • Close genetic similarity to EHV-4 strains from Australia and Japan.
    • A distant relationship to other European EHV-4 strains, but with limited sequence data available from Europe, making comprehensive comparisons difficult.

Conclusions and Implications

  • The study demonstrates how EHV-4 can spread within a veterinary hospital setting and highlights the value of detailed clinical monitoring combined with molecular diagnostics.
  • Sequencing played a critical role in:
    • Identifying transmission chains during the outbreak.
    • Differentiating new cases due to different viral strains from the initial outbreak cases.
    • Characterizing the genetic makeup of the circulating virus.
  • Findings from this study can inform future outbreak control strategies in equine facilities by emphasizing the importance of testing, biosecurity, and molecular surveillance.

Cite This Article

APA
Ryt-Hansen P, Johansen VK, Cuicani MM, Larsen LE, Hansen S. (2024). Outbreak of equine herpesvirus 4 (EHV-4) in Denmark: tracing patient zero and viral characterization. BMC Vet Res, 20(1), 287. https://doi.org/10.1186/s12917-024-04149-x

Publication

BMC veterinary research
ISSN: 1746-6148
NlmUniqueID: 101249759
Country: England
Language: English
Volume: 20
Issue: 1
Pages: 287
PII: 287

Researcher Affiliations

Ryt-Hansen, Pia
  • Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Grønnegårdsvej 2, Frederiksberg C, DK-1870, Denmark. piarh@sund.ku.dk.
Johansen, Victoria Kyhl
  • Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Grønnegårdsvej 2, Frederiksberg C, DK-1870, Denmark.
Cuicani, Marta Maria
  • Statens Serum Institut, Artillerivej 5, Copenhagen S, 2300, Denmark.
Larsen, Lars Erik
  • Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Grønnegårdsvej 2, Frederiksberg C, DK-1870, Denmark.
Hansen, Sanni
  • Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Taastrup, Denmark.

MeSH Terms

  • Animals
  • Horses
  • Horse Diseases / virology
  • Horse Diseases / epidemiology
  • Disease Outbreaks / veterinary
  • Denmark / epidemiology
  • Herpesviridae Infections / veterinary
  • Herpesviridae Infections / epidemiology
  • Herpesviridae Infections / virology
  • Herpesvirus 4, Equid / isolation & purification
  • Male
  • Female
  • Antibodies, Viral / blood
  • Hospitals, Animal

Conflict of Interest Statement

The authors declare no competing interests.

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Citations

This article has been cited 2 times.
  1. Tallmadge RL, Laverack M, Lejeune M, Crossley B, Diel DG. A multiplex real-time PCR assay for detection of equid herpesvirus 1 and 4. Sci Rep 2025 Oct 31;15(1):38201.
    doi: 10.1038/s41598-025-22043-wpubmed: 41173927google scholar: lookup
  2. Kutumbetov L, Myrzakhmetova B, Tussipova A, Zhapparova G, Tlenchiyeva T, Bissenbayeva K, Nurabayev S, Kerimbayev A. Development and Preclinical Evaluation of a Lyophilized Vaccine Against Equine Herpesvirus Type 4 (EHV-4). Vaccines (Basel) 2025 May 31;13(6).
    doi: 10.3390/vaccines13060604pubmed: 40573935google scholar: lookup
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