The Virulence And Mechanism Of Th005(H7N9) In Ferrets,mice,and Chickens

Background After the first appearance of H7N9 avian influenza virus infection in humans in 2013,there were four continuous H7N9 outbreaks in the following five years.The number of people infected with the fifth wave of H7N9 subtype influenza virases in 2017 equalled the total number infected in the first four outbreaks.The World Organisation for Animal Health(OIE)reported a large number of chicken deaths in farms and the H7N9 avian influenza virus was isolated from dead chickens.Objective As the prevalence of the fifth wave of outbreaks surges,it is necessary to track the changes in pathogens during this wave,especially the changes in virulence of the virus strains isolated from patients in mammals and avians respectively,and analyze their molecular mechanisms.Methods The pathogenicity and transmissibility of die Th005,which isolated from the fifth pandenic wave and the Anhui,which isolated from the first pandemic wave were evaluated and compared with ferrets via respiratory droplets and the intravenous pathogenicity index(IVPI)test in chickens.Virases isolated from H7N9-infected ferrets or chickens were used to infect mice and chickens to further analyse changes in the viral pathogenicity after the H7N9 avian influenza viruses were circulated in mammals and avians.In vitroy we analyzed the possible molecular mechanisms of the changes in virulence and transmissibility of the virases or viruses eirculated in different hosts through the dynamic replication curve of the viruses in different cell lines,receptor binding assay and viral genome sequencing.Results The results showed that the pathogenic ability of Th005 was significantly increased in ferrets and chickens,especially compared with Anhui strain,the replication ability of Th005 in lung tissues of ferrets was 100 times higher than Anhui strain.Compared with Anhui strain,Th005 strain exhibited no increase in aerosol transmissibility between ferrets.Th005 pathogenicity of IVPI score reached 3 in avians.Continuous high titer of virus could be detected in the cloacal cavity of chickens infected with Th005.The Th005 remained highly pathogenic to mice and chickens after circulating in ferrets.The virulence of Anhui strain was further increased after circulated in ferrets and chickens,and slightly increased after circulated in chickens.In vitro,high expression of sialic acid-a2,6-and a2,3-linkage cell was beneficial to the replication of Th005,and its replication ability was stronger than that of Anhui strain.The insertion of basic amino acids into the haemagglutinin(HA)cleavage site caused Th005 to become a highly pathogenic avian influenza virus,meanwhile,Th005 exhibited high pathogenicity to mammals without prior adaption and the pathogenicity of Th005 was even higher than that of Anhui,which might be caused by PB2-R526 of Th005.The dual receptor binding affinity of Th005 might be relevant to HA-V186 and HA-Q226.Conclusion The pathogenicity of Th005 in mammals further increased,compared with the strong strain Anhui isolated in the first epidemic,which enhanced the threat to human.However,since the transmissibility via droplets was not significantly improved,the outbreak of Th005 strain in public was still under control.Th005 exhibited high pathogenicity to poultry and would lead to high viral sheddding,which may cause damage to poultry industry and increase the enrichment of viruses in the environment.Surveillance for the H7N9 influenza virases,such as Th005,which had risen the virulence,should be stepped up.