OmniVira

No evidence of H5N1 avian influenza virus infection in Japanese horses in 2025.

Nanako Kawanishi1 Takahiro Hiono2,3,4,5 Yoshinori Kambayashi1 Hiroshi Bannai1 Koji Tsujimura1 Takashi Yamanaka6 Norikazu Isoda2,3,4,5 Yoshihiro Sakoda2,3,4,5 Manabu Nemoto7
Affiliations 7 institutions
  1. Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan.
  2. Laboratory of Microbiology, Department of Disease Control, Faculty of Veterinary Medicine, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan
  3. One Health Research Center, Hokkaido University, Kita 18, Nishi 9, Kita-ku, Sapporo, Hokkaido, 060-0818, Japan
  4. International Collaboration Unit, International Institute for Zoonosis Control, Hokkaido University, Kita 20, Nishi 11, Kita-ku, Sapporo, Hokkaido, 001-0020, Japan
  5. Institute for Vaccine Research and Development (HU-IVReD), Hokkaido University, Kita 21, Nishi 11, Kita-ku, Sapporo, Hokkaido, 001-0021, Japan.
  6. Miho Training Center Racehorse Clinic, Japan Racing Association, 2500-2, Mikoma, Miho, Ibaraki, 300-0415, Japan.
  7. Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi, 329-0412, Japan. Electronic address: [email protected].
PMID42648659 DOI10.1016/j.jevs.2026.106131 Year2026 Journal Journal of equine veterinary science J Equine Vet Sci Languageeng Publication statusActive
Active Last checked 2026-09-29 03:30:36 Source: NCBI PubMed

Abstract

The global spillover of clade 2.3.4.4b H5N1 highly pathogenic avian influenza virus into mammalian hosts has become a public health concern as well as to 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 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.

Supporting text Virus Host Location
Avian influenza 58 Equine influenza 1 H5N1 88 Interspecies transmission 55 Serosurveillance 3

Evidence records

1 total
Zoonotic Surveillance
1 records · 1 evidence types
Evidence type Serological Evidence
1 records
OVE12044 Serological Evidence
Key finding

In 2025 serosurveillance of 400 Japanese horses found no detectable H5N1 antibodies by HI, with 399/400 cELISA-negative and one doubtful sample.

Virus
Influenza A virus H5N1
Host
horse Equus caballus Natural host
Location
Not specified
Supporting text

Therefore, we conducted a serosurveillance study to assess the prevalence of H5N1 antibodies collected from 400 horses in Japan. 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.

Method
competitive ELISA (cELISA) | hemagglutination inhibition (HI) test
Sample type
serum