Decoding non-human mammalian adaptive signatures of 2.3.4.4b H5N1 to assess its human adaptive potential

ABSTRACT The recent panzootic 2.3.4.4b clade H5N1 infected diverse non-human mammalian species globally, showed mammal-to-mammal transmission among them and caused sporadic human infections. However, whether 2.3.4.4b H5N1 circulating in non-human mammals can establish human infections and spread among humans is unclear. Gain-of-function research restrictions preclude assessing human adapting mutations of 2.3.4.4b H5N1. Here, we tracked the evolution of 2.3.4.4b H5N1 that infected non-human mammals and evaluated their ability to gain human adaptations. The non-human mammal 2.3.4.4b H5N1 partly acquired classical human adapting mutations, which are identical to the residues of H1N1pdm09 and seasonal human H3N2 infections while showing a few species-specific adaptations that might be potential barriers for successful human adaptations. Despite minimal changes in Hemagglutinin (HA), A160T and T199I mutations near the receptor binding site of HA in dairy cattle viruses indicate the rapid HA glycan surface evolution affecting virus entry and immune evasion. The quantitative assessment indicated that 2.3.4.4b H5N1 circulating in bears, cattle, dolphins, and foxes show higher human adaptive potential than other hosts. Also, H5N1 infections in mammals across time showed a unique set of adaptations in the 2.3.4.4b clade compared to previously circulating strains, especially the acquisition of Q591 adaptation in PB2 that enables human adaptation. Thus, 2.3.4.4b H5N1 acquires human adaptations due to natural selection pressure in non-human mammals. Overall, our study delineates human adaptation and infection risk of specific non-human mammalian circulating HPAI 2.3.4.4b H5N1 strains. Competing Interest Statement The authors have declared no competing interest.