New study explores ability of swine flu to spread in cattle

An article co-authored by the Director of the Center of Excellence for Emerging and Zoonotic Animal Diseases (www.ceezad.org) and the Center on Emerging and Zoonotic Infectious Diseases (CEZID; https://www.k-state.edu/cezid/) reports on the results of research into the spread of the H3N2 swine influenza virus in calves.

The article was co-authored by Dr. Juergen A. Richt, Regents and University Distinguished Professor at Kansas State University and director of CEEZAD and CEZID. It was published in the July 9 edition of mBio.

Unprecedented outbreaks caused by the H5N1 highly pathogenic avian influenza virus (HPAIV) among dairy cows in the United States have raised significant concerns. Whether other subtypes of influenza A viruses (IAVs) can infect and transmit in cattle remains largely unknown.

In this study, researchers infected cattle cells with different IAVs and two groups of Holstein calves intranasally or orally with a swine H3N2 virus to determine their susceptibility. Naive calves were co-housed with infected animals to investigate virus transmission.

Results showed that swine and avian IAVs could infect cattle primary nasal turbinate and tracheal epithelial cells, as well as immortalized mammary gland epithelial cells and fibroblasts. After intranasal and oral inoculation, no obvious clinical signs were observed in infected and contact calves, but macroscopic lung lesions were found in animals form both inoculated groups on day 5 post-infection. Viral shedding was detected in three out of four intranasally infected calves but not in orally infected or the two groups of contact animals. Interestingly, viral RNA and antigen could not be detected in tissues from individual necropsied animals from either infection group, but viral RNA was detected in serum samples of two nasally infected calves on day 7 post-infection. Additionally, only the nasally infected animals seroconverted.

The results indicate that in addition to H5N1 HPAIV, swine H3N2 virus can infect cattle but does not transmit efficiently among them, suggesting that other subtypes of IAVs could infect and replicate in cattle. The results also demonstrate that different subtypes of IAVs can infect cattle and might pose threats to public and animal health.

The full study can be accessed by following this link. Outcomes of experimental infection of calves with swine influenza H3N2 virus | mBio. https://journals.asm.org/doi/10.1128/mbio.03957-24