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No evidence of H5N1 avian influenza virus infection in Japanese horses in 2025.
Abstract: The global spillover of clade 2.3.4.4b H5N1 highly pathogenic avian influenza virus into mammalian hosts has become a concern for public health as well as for the equine industry. However, previous reports on H5N1 natural infection and the presence of specific antibodies in horses remain limited. Therefore, we conducted a serosurveillance study to assess the prevalence of H5N1 antibodies in serum samples collected from 400 horses in Japan. Samples were screened using competitive ELISA (cELISA) and hemagglutination inhibition (HI) tests against H5-recombinant protein and H5N1 viral antigen, respectively. Of the 400 samples, 399 (99.75%) were negative by cELISA, while one sample (0.25%) yielded a doubtful result. However, all samples showed HI titers of <8, confirming the absence of H5N1 antibodies. These findings indicate that the current risk of H5N1 infection among horses in Japan remains limited. Nonetheless, continuous global surveillance is warranted to monitor the potential risk of H5N1 spillover into equine populations.
Copyright © 2026 Elsevier Inc. All rights reserved.
Publication Date: 2026-08-26 PubMed ID: 42648659DOI: 10.1016/j.jevs.2026.106131Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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Overview
- This study investigated whether Japanese horses had been infected with the H5N1 avian influenza virus by testing blood samples for specific antibodies.
- The research found no evidence of H5N1 infection in the horses sampled, indicating a low current risk of this virus affecting horses in Japan.
Background and Significance
- The H5N1 avian influenza virus, especially clade 2.3.4.4b, is known for being highly pathogenic and capable of spreading from birds to mammals.
- Spillover infections from birds to mammals, including horses, are a public health and veterinary concern, as they can lead to outbreaks and possibly impact the equine industry economically.
- Despite this concern, there have been very few reports documenting natural infection or antibody presence against H5N1 in horses, leading to a knowledge gap.
Objective
- The study aimed to determine the prevalence of antibodies to H5N1 in horses in Japan, thus assessing their exposure and potential infection by this virus.
Methods
- Serum samples were collected from a total of 400 horses across Japan.
- Two main laboratory tests were used to detect H5N1 antibodies:
- Competitive ELISA (cELISA) screening targeting H5 recombinant protein, which is a sensitive assay to detect specific antibodies.
- Hemagglutination inhibition (HI) test against H5N1 viral antigen, which confirms the presence and level of antibodies that can inhibit virus activity.
Results
- In the cELISA test, 399 out of 400 horse serum samples (99.75%) tested negative, indicating no detectable antibodies.
- One sample (0.25%) gave a doubtful result in cELISA, but this was not confirmed by further testing.
- All samples had HI titers below 8, which is a standard cutoff indicating no significant antibody presence against H5N1.
- These results together verified that none of the horses showed evidence of H5N1 infection or past exposure.
Conclusions
- The absence of detectable H5N1 antibodies in horses suggests that this equine population was not infected by H5N1 in 2025.
- This finding implies that the current risk of spillover of H5N1 influenza virus from birds to horses in Japan is very low.
- Continuous and global surveillance remains important to promptly detect any future spillover events given the dynamic nature of influenza viruses and their ability to cross species barriers.
Implications
- Equine health and the related industry in Japan currently face minimal threat from H5N1 HPAI virus.
- Ongoing monitoring of influenza viruses in wild birds, domestic birds, and mammals, including horses, will help prevent potential future outbreaks.
- Early detection through such serosurveillance studies is essential for public health preparedness and for guiding veterinary control measures.
Cite This Article
APA
Kawanishi N, Hiono T, Kambayashi Y, Bannai H, Tsujimura K, Yamanaka T, Isoda N, Sakoda Y, Nemoto M.
(2026).
No evidence of H5N1 avian influenza virus infection in Japanese horses in 2025.
J Equine Vet Sci, 167, 106131.
https://doi.org/10.1016/j.jevs.2026.106131 Publication
Researcher Affiliations
- Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan.
- Laboratory of Microbiology, Department of Disease Control, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan; One Health Research Center, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan; International Collaboration Unit, International Institute for Zoonosis Control, Hokkaido University, Kita 20, Nishi 10, Kita-ku, Sapporo, Hokkaido, 001-0020, Japan; Institute for Vaccine Research and Development (HU-IVReD), Hokkaido University, Kita 21, Nishi 11, Kita-ku, Sapporo, Hokkaido, 001-0021, Japan.
- Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan.
- Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan.
- Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan.
- Miho Training Center Racehorse Clinic, Japan Racing Association, 2500-2, Mikoma, Miho, Ibaraki, 300-0415, Japan.
- Laboratory of Microbiology, Department of Disease Control, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan; One Health Research Center, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan; International Collaboration Unit, International Institute for Zoonosis Control, Hokkaido University, Kita 20, Nishi 10, Kita-ku, Sapporo, Hokkaido, 001-0020, Japan; Institute for Vaccine Research and Development (HU-IVReD), Hokkaido University, Kita 21, Nishi 11, Kita-ku, Sapporo, Hokkaido, 001-0021, Japan.
- Laboratory of Microbiology, Department of Disease Control, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan; One Health Research Center, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan; International Collaboration Unit, International Institute for Zoonosis Control, Hokkaido University, Kita 20, Nishi 10, Kita-ku, Sapporo, Hokkaido, 001-0020, Japan; Institute for Vaccine Research and Development (HU-IVReD), Hokkaido University, Kita 21, Nishi 11, Kita-ku, Sapporo, Hokkaido, 001-0021, Japan.
- Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan. Electronic address: nemoto_manabu@equinst.go.jp.
Conflict of Interest Statement
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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