Article explores dynamics of H5N1 clade 2.3.4.4b infection in calves and cows

February 9, 2025

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 examines the dynamics of the spread of H5N1 clade 2.3.4.4b in experimentally infected calves and cows.

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. Other co-authors include Konner Cool, Jessie D. Trujillo, Taeyong Kwon, Chester D. McDowell, Gagandeep Singh, Sujan Kafle, Natasha N. Gaudreault, and Igor Morozov, all of CEEZAD.

It was published in the January 2025 edition of the journal Nature.

In March 2024, highly pathogenic avian influenza virus (HPAIV) clade 2.3.4.4b H5N1 infections were reported in dairy cows in Texas. Rapid dissemination to more than 900 farms in 15 states followed. In this study researchers provide results of two independent clade 2.3.4.4b experimental infection studies evaluating the oronasal susceptibility to and transmission of a US H5N1 bovine isolate, genotype B3.13 (H5N1 B3.13), in calves, and the susceptibility of lactating cows following direct mammary gland inoculation of either H5N1 B3.13 or a current EU H5N1 wild bird isolate, genotype euDG (H5N1 euDG).

Inoculation of the calves resulted in moderate nasal replication and shedding with no severe clinical signs or transmission to sentinel calves. In dairy cows, infection resulted in no nasal shedding, but severe acute infection of the mammary gland with necrotizing mastitis and high fever, observed for both H5N1 isolates. Milk production was rapidly and markedly reduced and the physical condition of the cows was severely compromised.

Virus titers in milk rapidly peaked at 10⁹ 50% tissue culture infectious dose (TCID₅₀) per ml, but systemic infection did not ensue. Notably, the adaptive mutation E627K emerged in the viral polymerase basic protein 2 (PB2) after intramammary replication of wild bird H5N1 isolate.

The research data suggests that in addition to H5N1 B3.13, other HPAIV H5N1 strains have the potential to replicate in the udder of cows and that milk and milking procedures, rather than respiratory spread, are likely to be the primary routes of H5N1 transmission between cattle.

The full article can be read by following this link: https://pubmed.ncbi.nlm.nih.gov/39321846/#:~:text=Nature,2024%20Sep%2025