Detection of Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b, Genotype D1.1, in Wild Birds and a Human in British Columbia, Canada, 2024.

There have been four distinct ‘waves’ of HPAI A(H5N1) clade 2.3.4.4b in British Columbia (BC), Canada, with each wave being characterized by the emergence of new genotypes and shifts in the dominant genotype. In the first three waves, most viruses were ‘B’ genotype reassortant descendants of the HPAI virus introduced via the East Atlantic Flyway in 2021; however, in fall 2024, infections were primarily caused by a novel genotype (D1.1) that was a descendant of the A3 genotype introduced via the Pacific Flyway in 2021. This genotype, which was initially limited to BC, subsequently went on to become dominant throughout North America. We used whole genome sequencing with phylogenetic and phylodynamic analyses to characterize genotype D1.1 in wild birds and a human. The D1.1 genotype, which is the first HPAI clade 2.3.4.4b genotype to include a North American NA segment, may have originated in BC through reassortment with low-pathogenicity H1N1 found in mallards. D1.1 was associated with record levels of HPAI environmental contamination and infections in poultry in BC, suggesting that the novel NA segment could impact host-virus interactions. There was also a case of human infection with a D1.1 virus most closely related to those found in wild birds, highlighting the importance of understanding D1.1 host range and infectivity. The D1.1 HA segment displayed less genetic divergence than expected, suggesting the genotype or its ancestors may have been preserved in an environmental reservoir or become adapted to wild birds.

British Columbia Ministry of Agriculture and Food, Abbotsford, British Columbia, Canada (C.G. Himsworth, A. Redford, T. Burns), British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada (J. Caleta, A. N. Jassem, K. Yang, J.E.A. Zlosnik, J.R, Tyson, K. Kuchinski, N. Prystajecky, S.L. Russell), Canadian Wildlife Service-Environment and Climate Change Canada, Delta, British Columbia, Canada (L. Wilson, M. Willie), Environment and Climate Change Canada, Ottawa, Ontario, Canada (J. Giacinti), British Columbia Ministry of Water, Land and Resource Stewardship, Nanaimo, British Columbia, Canada (M. Winchester, C. Thacker), Canadian Food Inspection Agency, Winnipeg, Manitoba, Canada (Y. Berhane)

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