Novel H5N6 reassortants bearing the clade 2.3.4.4b HA gene of H5N8 virus have been detected in poultry and caused multiple human infections in China

Abstract

The globally circulating H5N8 avian influenza viruses bearing the clade 2.3.4.4b hemagglutinin (HA) gene are responsible for the loss of more than 33 million domestic poultry since January 2020. Moreover, the H5N8 viruses have reassorted with other avian influenza viruses and formed H5N1, H5N2, H5N3, H5N4, and H5N5 viruses in Europe, Africa, and North America. In this study, we analyzed 15 H5N6 viruses isolated from poultry and seven H5N6 viruses isolated from humans, and found these viruses formed seven different genotypes by deriving the clade 2.3.4.4b HA gene of H5N8 viruses, the neuraminidase of domestic duck H5N6 viruses, and internal genes of different viruses that previously circulated in domestic ducks and wild birds in China. Two of these genotypes (genotype 3 and genotype 6) have caused human infections in multiple provinces. The H5N6 viruses isolated from poultry have distinct pathotypes in mice; some of them replicate systemically and are highly lethal in mice. Although these viruses exclusively bind to avian-type receptors, it is worrisome that they may obtain key mutations that would increase their affinity for human-type receptors during replication in humans. Our study indicates that the novel H5N6 reassortants bearing the clade 2.3.4.4b HA gene of H5N8 viruses were generated through reassortment in domestic ducks and may have spread across a wide area of China, thereby posing a new challenge to the poultry industry and human health. Our findings emphasize the importance of careful monitoring, evaluation, and control of the H5N6 viruses circulating in nature.

Global dissemination of H5N1 influenza viruses bearing the clade 2.3.4.4b HA gene and biologic analysis of the ones detected in China

“…Gu et al detected different genotypes of H5N6 viruses in China and found that the H5N6 viruses were reassortants that derived their HA genes from H5N8 viruses, NA genes from different duck H5N6 viruses, and certain internal genes from different low pathogenic viruses [ 15 ]. Most of the donor viruses of the NA and internal genes of the H5N6 viruses were previously detected in China, suggesting that the H5N6 reassortants were generated in ducks in China [ 15 ]. However, it seems that the four genotypes of the H5N1 viruses detected in China have not undergone any further reassortment in domestic birds in China.…”

“…The H5 avian influenza viruses are becoming progressively more virulent in the mammalian mouse model. Some of the earliest H5N1 viruses could not replicate in mice [ 36 ], but more and more strains have now acquired this ability and some have become lethal in mice [ 4 , 10 , 15 ]. A series of amino acid substitutions in different proteins of avian influenza virus have been reported to increase its pathogenicity to mice [ 37–53 ], and many of these substitutions have been detected in the widely circulating H5N1 viruses, which explains why the H5N1 viruses we tested in this study were able to replicate in and kill mice.…”

“…The nucleotide sequence was edited by using the Seqman module of the DNAStar package. The HA gene tree was generated with the HA of 263 H5 viruses bearing clade 2.3.4.4b HA, including 250 viruses (eight H5N6 human viruses, 22 H5N8 representative viruses, and 220 H5N1 representative viruses) reported previously by us and others [ 10 , 15 , 16 , 18 , 22–25 ] and 13 H5N1 viruses detected in China in this study. Phylogeographic analysis was performed using an asymmetric continuous-time Markov chain with Bayesian stochastic search variable selection implemented in BEAST (v1.10.4) [ 26 ].…”

“…At the beginning of 2020, H5N8 viruses bearing the clade 2.3.4.4b HA gene infected domestic poultry and wild birds, leading to the loss of over 33 million domestic birds in Europe, Africa, and Asia [ 10–13 ]. Moreover, these H5N8 viruses reassorted with other avian influenza viruses and formed H5N1, H5N2, H5N3, H5N4, H5N5, and H5N6 viruses [ 11 , 14 , 15 ]. Unlike the H5N2, H5N3, H5N4, H5N5, and H5N6 viruses, each of which has only been detected in countries of one or two continents, the H5N1 viruses bearing the clade 2.3.4.4b HA gene have spread to many countries in Europe, Africa, Asia, and America since they emerged in October 2020 in the Netherlands [ 16–19 ].…”

Evolutionary and Mutational Characterization of the First H5N8 Subtype Influenza A Virus in Humans

“…All Astrakhan viruses in 2020 had 137A/158N/160A/186N residues in their HA proteins, which have been reported to increase the affinity to α-2,6 sialic acids. A recent study showed that new H5N6 reassortants bearing the HA gene of H5N8 virus clade 2.3.4.4b caused multiple human infections [24]. This virus generated in nature instead of a reverse genetically engineered virus in the laboratory demonstrated that both H5N8 and H5N6 viruses carrying the HA gene can mediate human infections.…”