Pathogenicity and Transmissibility of Clade 2.3.4.4h H5N6 Avian Influenza Viruses in Mammals

Simple Summary In the past decade, the spread of H5N6 avian influenza viruses (AIVs) in birds and infection in humans has attracted increasing global attention, and these viruses have the potential to become a pandemic threat to global health. In this study, the HA genes of the HB1907 and HB1905 AIVs were clustered in the 2.3.4.4h clade, and the HA genes of both strains exhibited highly pathogenic avian influenza virus (HPAIV) characteristics. The HB1905 strain in this study has a binding preference for avian-like (alpha-2,3) receptors only, whereas the HB1907 strain has a binding preference for both avian-like (alpha-2,3) and human-like (alpha-2,6) receptors. Compared with the HB1905 strain, the HB1907 strain showed better replication ability in MDCK cells in the early stage of infection. At the same time, the HB1907 strain showed advantages in the pathogenicity of mice and the transmission ability of direct contact between guinea pigs. These results further suggest that epidemiological surveillance and the related studies of H5N6 AIVs are essential for public health safety and the healthy and sustainable development of the livestock industry. Avian influenza viruses (AIVs) have the potential for cross-species transmission and pandemics. In recent years, clade 2.3.4.4 H5N6 AIVs are prevalent in domestic poultry, posing a threat to the domestic poultry industry and public health. In this study, two strains of H5N6 AIVs were isolated from chickens in Hebei, China, in 2019: A/chicken/Hebei/HB1907/2019(H5N6) and A/chicken/Hebei/HB1905/2019(H5N6). Phylogenetic analysis showed that both viral HA genes clustered in the 2.3.4.4h clade. Receptor binding analysis showed that the HB1905 strain preferentially binds to alpha-2,3-linked sialic acid (SA) receptors, while the HB1907 strain preferentially binds to alpha-2,3- and alpha-2,6-linked sialic acid (SA) receptors. During early infection, the HB1907 strain is highly replicable in MDCK cells, more so than the HB1905 strain. Pathogenicity assays in mice showed that both viruses could replicate in the lungs without prior adaptation, with HB1907 being more highly pathogenic in mice than the HB1905 strain. Significantly, both the HB1905 and HB1907 strains can be transmitted through direct contact among guinea pigs, but the transmission efficiency of the HB1907 strain through contact between guinea pigs is much greater than that of the HB1905 strain. These results strengthen the need for ongoing surveillance and early warning of H5N6 AIVs in poultry.