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Volume 32, Number 5—May 2026

Research Letter

Highly Pathogenic Avian Influenza A(H5N1) Virus RNA in Bovine Semen, California, USA, 2024

Ailam Lim1Comments to Author , Keith Poulsen1, Leonardo C. Caserta, Lizheng Guan, Eryn Opgenorth, Maxwell P. Beal, Amie J. Eisfeld, Yoshihiro Kawaoka, and Diego G. Diel
Author affiliation: University of Wisconsin–Madison Wisconsin Veterinary Diagnostic Laboratory, Madison, Wisconsin, USA (A. Lim, K. Poulsen, E. Opgenorth); University of Wisconsin–Madison, Madison (A. Lim, K. Poulsen, L. Guan, A.J. Eisfeld, Y. Kawaoka); Cornell University Animal Health Diagnostic Center, College of Veterinary Medicine, Ithaca, New York, USA (L.C. Caserta, D.G. Diel); Mill Creek Veterinary Services, Visalia, California, USA (M.P. Beal); Dakota Dairy Health, Brookings, South Dakota, USA (M.P. Beal); University of Tokyo Institute of Medical Science, Tokyo, Japan (Y. Kawaoka); University of Tokyo Pandemic Preparedness, Infection and Advanced Research Center, Tokyo (Y. Kawaoka); Japan Institute for Health Security, National Institute of Global Health and Medicine, Tokyo (Y. Kawaoka)

Main Article

Table

Influenza A virus testing results for samples collected from 3 bulls in HPAI H5N1–infected farm in study of HPAI H5N1 virus RNA in bovine semen, California, USA, 2024*

Bull no. Specimen type IAV ELISA result (sample/positive control ratio) IAV RT-PCR
result (Ct)†		 H5 RT-PCR result (Ct)† Clade 2.3.4.4b RT-PCR result (Ct)† Virus isolation
Bull 1 Serum Negative (0.620) NP NP NP Negative
Deep nasal swabs NP Negative NP NP Negative
Preputial scrape NP Negative NP NP Negative
Preejaculate NP Negative NP NP Negative
Semen NP Detected:‡
detected (38.2/39.5);§
negative/detected (39.1);¶ detected (37.9/38.9)#
 Negative Detected (39.6) Negative
Bull 2
 Serum Negative (1.000) NP NP NP NP
Deep nasal swabs NP Negative NP NP NP
Preputial scrape NP Negative NP NP NP
Preejaculate NP Negative NP NP NP
Semen
 NP
 Negative
 NP
 NP
 NP
Bull 3 Serum Negative (0.880) NP NP NP NP
Deep nasal swabs NP Negative NP NP NP
Preputial scrape NP Negative NP NP NP
Preejaculate and semen NP Negative NP NP NP

*Ct, cycle threshold; HPAI, highly pathogenic avian influenza; IAV, influenza A virus; NP, not performed; RT-PCR, reverse transcription PCR. †Assay Ct cutoff value was 40. ‡Sample was subjected to further sequencing analyses. §Wisconsin Veterinary Diagnostic Laboratory IAV assay, tested in duplicate. ¶National Animal Health Laboratory Network IAV Matrix assay, tested in duplicate. #Modified National Animal Health Laboratory Network IAV Matrix assay, tested in duplicate.

Main Article

1These authors contributed equally to this article.

Page created: March 23, 2026
Page updated: May 08, 2026
Page reviewed: May 08, 2026
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