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One health (Amsterdam, Netherlands)2026; 23; 101505; doi: 10.1016/j.onehlt.2026.101505

First evidence of exposure to West Nile Virus in horses within Denmark, 2025.

Abstract: A nationwide serological screening of 822 horses was conducted in Autumn 2025 to investigate potential exposure to West Nile Virus (WNV) within Denmark. Serum samples were tested for antibodies against WNV, tick-borne encephalitis virus (TBEV) and Usutu virus (USUV). Four horses without any history of travel outside of Denmark, or previous vaccination against WNV, tested positive for WNV neutralising antibodies. The results support local exposure to WNV indicating that virus infected mosquitoes have been present in Denmark and underline the usefulness of horses as sentinels for the risk of human exposure.
© 2026 Published by Elsevier B.V.
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Publication Date: 2026-06-29 PubMed ID: 42440749PubMed Central: PMC13334394DOI: 10.1016/j.onehlt.2026.101505Google 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.

Overview

  • This study conducted a nationwide serological screening of horses in Denmark to detect exposure to West Nile Virus (WNV) for the first time.
  • It found evidence that some horses without travel history had been exposed to WNV, suggesting local presence of the virus in Denmark.

Background and Purpose

  • West Nile Virus (WNV) is a mosquito-borne virus that can infect birds, horses, and humans, sometimes causing neurological disease.
  • Denmark had no prior documented evidence of WNV exposure, so understanding whether WNV is present locally is important for animal and human health surveillance.
  • Horses are valuable sentinels for detecting the presence of WNV because they develop antibodies if infected, even if they do not show symptoms.
  • The study aimed to screen a large number of horses across Denmark for antibodies to WNV and related viruses to investigate possible exposure.

Methods

  • A total of 822 horses were sampled nationwide during Autumn 2025, representing a broad geographic area in Denmark.
  • Serum samples were tested for neutralising antibodies against three flaviviruses: West Nile Virus (WNV), tick-borne encephalitis virus (TBEV), and Usutu virus (USUV), to differentiate the specific cause of seropositivity.
  • Horses selected had no history of travel outside Denmark or previous vaccination against WNV to exclude imported exposure or vaccine-induced antibodies.

Findings

  • Four horses tested positive for WNV neutralising antibodies, despite never leaving Denmark or being vaccinated.
  • No antibodies to TBEV or USUV were reported as positive in these cases, suggesting specific exposure to WNV rather than cross-reactivity.
  • This constitutes the first serological evidence of WNV circulation in Denmark.
  • The presence of antibodies implies that infected mosquitoes carrying WNV have recently been in Denmark.

Implications

  • This study confirms local transmission of West Nile Virus in Denmark, which was previously undocumented.
  • It highlights that WNV-infected mosquitoes have established or are intermittently present in the Danish ecosystem.
  • Horses prove to be effective sentinels for the risk of WNV exposure impacting both animal and potentially human populations.
  • These findings underscore the need for continued monitoring and consideration of WNV in veterinary and public health strategies in Denmark.

Conclusions

  • The detection of WNV antibodies in non-traveling horses provides the first evidence of West Nile Virus exposure within Denmark.
  • Ongoing surveillance in horses and mosquitoes is important to track the spread and risk of WNV locally.
  • Preventive measures and awareness may be warranted to mitigate the impact of WNV on horses and public health in Denmark.

Cite This Article

APA
Ryt-Hansen P, Kallehauge-Larsen CE, Gonzalez G, Migné CV, Larsen LE, Gelskov LV, Lohse L, Hansen S, Olesen AS. (2026). First evidence of exposure to West Nile Virus in horses within Denmark, 2025. One Health, 23, 101505. https://doi.org/10.1016/j.onehlt.2026.101505

Publication

One health (Amsterdam, Netherlands)
ISSN: 2352-7714
NlmUniqueID: 101660501
Country: Netherlands
Language: English
Volume: 23
Pages: 101505
PII: 101505

Researcher Affiliations

Ryt-Hansen, Pia
  • Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg C, Denmark.
Kallehauge-Larsen, Camilla E
  • Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg C, Denmark.
Gonzalez, Gaëlle
  • ANSES, INRAE, Ecole Nationale Vétérinaire d'Alfort, UMR 1161 Virologie, Laboratoire de Santé Animale, Maison-Alfort, France.
Migné, Camille Victoire
  • ANSES, INRAE, Ecole Nationale Vétérinaire d'Alfort, UMR 1161 Virologie, Laboratoire de Santé Animale, Maison-Alfort, France.
Larsen, Lars Erik
  • Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg C, Denmark.
Gelskov, Laura Vebæk
  • Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg C, Denmark.
  • Section for Veterinary Virology, Department of Virology & Microbiological Preparedness, Statens Serum Institut, Copenhagen, Denmark.
Lohse, Louise
  • Section for Veterinary Virology, Department of Virology & Microbiological Preparedness, Statens Serum Institut, Copenhagen, Denmark.
Hansen, Sanni
  • Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Taastrup, Denmark.
Olesen, Ann Sofie
  • Section for Veterinary Virology, Department of Virology & Microbiological Preparedness, Statens Serum Institut, Copenhagen, Denmark.

Conflict of Interest Statement

None declared.

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