Dairy #cows infected with #influenza #H5N1 reveals low infectious dose and #transmission #barriers

 

Abstract

Highly pathogenic avian influenza A(H5N1) virus exhibits a strong tropism for the bovine mammary gland, challenging our understanding of influenza A virus host range and tissue specificity. We performed experimental studies with an influenza A(H5N1) B3.13 genotype virus in female lactating dairy cattle to define the infectious dose, routes of exposure, and factors linked to morbidity and mortality. Here, we demonstrate that intramammary inoculation with as few as 10 TCID50 establishes a robust infection and shedding of high-titer virus in milk. Despite this low infectious dose, H5N1 does not readily transmit via contaminated milking equipment and close contact with infected animals. High-dose intramammary exposure results in severe disease and mortality, while respiratory and oral exposures are less likely to establish productive infection and associated morbidity. This study challenges current hypotheses of H5N1 transmission on dairy farms, raising important questions about potential agent, host, or environmental cofactors contributing to viral spread.

Source: 

Link: https://www.nature.com/articles/s41467-026-73490-6

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Spatiotemporal #Dynamics of Highly Pathogenic Avian #Influenza #H5 Virus Introductions and Regional Spread in the Republic of #Korea

 

Abstract

Highly pathogenic avian influenza (HPAI) viruses from clade 2.3.4.4 have caused recurrent outbreaks in poultry since 2014. In the Republic of Korea, clade 2.3.4.4b viruses have driven five epidemic waves, yet the factors underlying HPAI introduction and farm-to-farm spread remain poorly understood. We compiled hemagglutinin gene sequences of clade 2.3.4.4b viruses from wild birds and poultry in the Republic of Korea (October 2016–March 2024) and reconstructed dispersal dynamics using Bayesian phylogeography. Dispersal patterns suggest that domestic duck farms in the western provinces likely form a key interface for spillover from wild birds into poultry. Mixed-effects generalized linear models showed that both wild-to-poultry and farm-to-farm transition rates were positively associated with the number of poultry farms in the destination province, while wild-to-poultry rates were further associated with higher avian influenza virus infection probability among wild birds. Wild-to-poultry transition rates were lower in 2020–2024 than in 2016–2018, which may reflect strengthened interventions. These findings suggest that poultry farm abundance and introduction pressure from wild birds jointly shape the spatial dynamics of HPAI introduction and spread. More broadly, these factors may provide operational indicators to guide risk-based surveillance and control strategies.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.21.726857v1

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Understanding the emergence of the #influenza #H3N2 K #subclade in its historical and evolutionary context

Abstract

The emergence in 2025/26 of the influenza A/H3N2 K substrain (H3N2/K) was the cause of significant public health concern. This genetically divergent virus was assessed to have a strongly decreased reactivity to contemporary vaccine strains. Respectively prolonged and early influenza seasons in the Southern and Northern Hemispheres contributed to concerns about vaccine efficacy. Here we retrospectively assessed the genetic and antigenic properties of this virus, combining epidemiological surveillance data, computational antigenic analysis, and serological data using samples from a well-stratified UK cohort. In contrast to initial indications, we found that despite the genetic distinctiveness of H3N2/K the virus had undergone limited antigenic change, suggesting that its emergence was instead the result of selection for non-antigenic properties. We confirmed previous results showing that contemporary vaccines produced an enhanced neutralising response to H3N2/K but, in a stratified serological analysis, showed that responses to the J and K substrains were age-dependent, largely driven by patterns of vaccination. Our results have implications for antigenic surveillance and for public communication strategies in future influenza seasons.

Competing Interest Statement

PRM declares funding by MSD. EH has received an honorarium for advisory board work for Seqirus.

Funder Information Declared

Medical Research Council, MR/Y03368X/1, MC_UU_0034/1, MC_UU_0034/2, MC_UU_0034/3, MC_UU_0034/5, MC_UU_0034/6

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.21.726823v1

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