The PB2 E627K mutation in the viral polymerase of H5N1 (colloquially known as bird flu) allows for interaction with the mammalian gene ANP32A [1] for optimal viral replication. [1] Such host switching can be of grave public health concern. [2] [3] [4] It was first noted in the scientific literature in February 2014, [5] and emerged in the then-novel highly pathogenic avian influenza A(H5N1) clade in 2020. [6] Host adaptation has been noted as being "rapid"; [7] the most recent outbreak was posited to be in San Bernardino County, California dairy cow herds in March 2025. [8]
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