Analysis Of The Receptor Binding Specificity Of Clade 2.3.4.4 H5 Subtype Avian Influenza Virus And The Biological Characteristic Of The Newly Emerging H5N8 Subtype Avian Influenza Viruses

According to the phylogenetic relationship and the difference of amino acid sites in the receptor binding region of HA,we selected 52 viruses of clade 2.3.4.4 isolated between 2013 and 2020 to analyze their receptor binding specificity,and it was revealed that some viruses had dual receptor binding specificity,which had high affinity to ?-2,3 linked glycans(avian-type receptor)and medium affinity to ?-2,6 linked glycans(human-type receptor).Furthermore,some viruses with medium affinity to human-type receptor could transmit among guinea pigs by direct contact,which had the potential risk to transmit in humans.It was suggested that the amino acid sites at 133,155 and 193 of HA protein played an important role for clade 2.3.4.4 viruses to bind human type receptors.The H5N8 avian influenza viruses have been widely circulating in wild birds and are responsible for the loss of over 33 million domestic poultry in Europe,Russia,Middle East,and Asia since January 2020.To monitor the invasion and spread of the H5N8 virus in China,we performed active surveillance in wild birds and in domestic poultry from September 2020 to June 2021.We collected 317 wild bird samples,and 41,172 poultry swab samples.A total of 36 H5N8 avian influenza viruses were isolated from these samples:22 viruses were isolated from wild bird samples,and eight and six viruses were isolated from duck swabs and goose swabs,respectively,that were collected in live poultry markets and slaughterhouses.Genetic analysis indicated that the 36 viruses formed two different genotypes:35 viruses belonging to genotype one(G1),which began to be detected in swans and spread to at least 16 different species of wild birds in China from October 2020,and were also detected in ducks and geese in 2021.In this study,only one virus belonged to genotype two(G2),which was detected in a whopper swan in January 2021,and we did not detect this type virus in poultry.Animal studies indicated that the H5N8 isolates are highly pathogenic to chickens,mildly pathogenic in ducks,but have distinct pathotypes in mice.Although there is more than 32-fold antigenic difference between the H5N8 viruses and the H5N1 vaccine strains Re-11 and Re-12 currently used in China,vaccinated chickens and ducks in poultry farms could be completely protected against H5N8 virus challenge.Given that the H5N8 viruses are likely to continue to spread in wild birds,vaccination of poultry is highly recommended in high-risk countries to prevent H5N8 avian influenza.