The evolution,pathogenicity and transmissibility of quadruple reassortant H1N2 swine influenza virus in China:A potential threat to public health

Swine are regarded as“intermediate hosts”or“mixing vessels”of influenza viruses,capable of generating strains with pandemic potential.From 2020 to 2021,we conducted surveillance on swine H1N2 influenza(swH1N2)viruses in swine farms located in Guangdong,Yunnan,and Guizhou provinces in southern China,as well as Henan and Shandong provinces in northern China.We systematically analyzed the evolution and pathogenicity of swH1N2 isolates,and characterized their replication and transmission abilities.The isolated viruses are quadruple reassortant H1N2 viruses containing genes from pdm/09 H1N1(PB2,PB1,PA and NP genes),triple-reassortant swine(NS gene),Eurasian Avian-like(HA and M genes),and recent human H3N2(NA gene)lineages.The NA,PB2,and NP of SW/188/20 and SW/198/20 show high gene similarities to A/Guangdong/Yue Fang277/2017(H3N2).The HA gene of swH1N2 exhibits a high evolutionary rate.The five swH1N2 isolates replicate efficiently in human,canine,and swine cells,as well as in the turbinate,trachea,and lungs of mice.A/swine/Shandong/198/2020 strain efficiently replicates in the respiratory tract of pigs and effectively transmitted among them.Collectively,these current swH1N2 viruses possess zoonotic potential,highlighting the need for strengthened surveillance of swH1N2 viruses.

Detection and pathogenesis of a novel swine H3N2 influenza virus containing three genes from the 2009 pandemic H1N1 influenza viruses in Korea in 2015

Dear Editor,Influenza A viruses cause pandemics at an interval of approximately 10–40 years,and pigs are regarded as a'mixing vessel'because they are easily infected with avian and human influenza viruses(Ito et al.,1998).According to previous studies,H3N2,H1N2,and

Generation and characterization of a cold-adapted attenuated live H3N2 subtype influenza virus vaccine candidate

Background H3N2 subtype influenza A viruses have been identified in humans worldwide, raising concerns about their pandemic potential and prompting the development of candidate vaccines to protect humans against this subtype of influenza A virus. The aim of this study was to establish a system for rescuing of a cold-adapted high-yielding H3N2 subtype human influenza virus by reverse genetics, Methods In order to generate better and safer vaccine candidate viruses, a cold-adapted high yielding reassortant H3N2 influenza A virus was genetically constructed by reverse genetics and was designated as rgAA-H3N2. The rgAA-H3N2 virus contained HA and NA genes from an epidemic strain A/Wisconsin/67/2005 （H3N2） in a background of internal genes derived from the master donor viruses （MDV）, cold-adapted （ca）, temperature sensitive （ts）, live attenuated influenza virus strain A/Ann Arbor/6/60 （MDV-A）. Results In this presentation, the virus HA titer of rgAA-H3N2 in the allantoic fluid from infected embryonated eggs was as high as 1：1024. A fluorescent focus assay （FFU） was performed 24-36 hours post-infection using a specific antibody and bright staining was used for determining the virus titer. The allantoic fluid containing the recovered influenza virus was analyzed in a hemagglutination inhibition （HI） test and the specific inhibition was found. Conclusion The results mentioned above demonstrated that cold-adapted, attenuated reassortant H3N2 subtype influenza A virus was successfully generated, which laid a good foundation for the further related research.

Molecular evolution of influenza A (H3N2) viruses cir-culated in Fujian Province, China during the 1996-2004 period

We studied the genetic and epidemic characteristics of influenza A (H3N2) viruses circulated in human in Fujian Province, south of China from 1996 to 2004. Phylogenetic analysis was carried out for genes encoding hemagglutinin1 (HA1) of influenza A virus (14 new and 11 previously reported reference se-quences). Our studies revealed that in the 8 flu seasons, the mutations of HA1 genes occurred from time to time, which were responsible for about four times of antigenic drift of influenza H3N2 viruses in Fujian, China. The data demonstrated that amino acid changes were limited to some key codons at or near antibody binding sites A through E on the HA1 molecule. The changes at the antibody binding site B or A or sialic acid receptor binding site 226 were critical for antigenic drift. But the antigenic sites might change and the key codons for antigenic drift might change as influenza viruses evolve. It seems important to monitor new H3 isolates for mutations in the positively selected codons of HA1 gene in south of Asia.

Emergence of truncated PB1-F2 protein of H3N2 influenza virus during its epidemic period in Jiangsu Province, China

Background PB1-F2 protein has been proven to increase the pathogenicity of influenza A virus （IAV） strains in primary infection and in secondary bacterial infection. It can also regulate the activity of viral polymerase. However, it was shown in another retrospective study that a portion of IAVs do not express full-length PB1-F2 protein during virus development; different kinds of stop codons cause exits in the open reading frames and form PB1-F2 gene products with the corresponding genotypes. Truncated PB1-F2 in human H3N2 IAVs has long been detected in North America but its evolution in China is still unclear. Methods Influenza-like illnesses （ILls） from the whole of Jiangsu Province were collected and inspected to determine the type and subtype of the viruses. A portion of isolates collected in the epidemic period were selected as samples for later whole-genome sequencing, and the exact sequences were determined and analyzed. Results H3N2 influenza virus was one of the epidemical strains which had been prevalent during 2009-2010, in Jiangsu. Five H3N2 isolates with truncated PB1-F2 protein （25aa） were detected in influenza samples from Nanjing and Xuzhou, while seven similar H3N2 isolates were also reported in Niigata, Japan. Conclusion This emergence indicates the possibility that there has been transmission of the H3N2 virus between the two countries.

Whole-genome sequences of two influenza A(H3N2)virus strains isolated from Qinghai,China

Influenza A(H3N2)virus has a faster evolution rate than other types of influenza viruses.In this study,whole genome sequencing was performed to better understand themolecular evolution of influenzaH3N2 and the protective effect of influenza virus vaccine in Qinghai Province,China,in 2017.Complete sequences of eight gene segments of two seasonal influenza H3N2 isolates were sequenced and analyzed using DNASTAR and MEGA 6.06 software.Additionally,the three-dimensional structure of the HA protein was predicted using the SWISS-MODEL server.Phylogenetic and amino acid sequence analysis revealed that two Qinghai H3N2 isolates were typical low-pathogenic influenza viruses,and were relatively closely related to the 2016–2017 vaccine strain,3C.2a-A/Hong Kong/4801/2014.The presence of several antigenic site substitutions(T131K,G/R142K,K160T and R261Q in the HA protein)were specific for the two Qinghai H3N2 virus strains.In addition,amino acid substitution of K160T at the glycosylation site of HA and H75P in PB1-F2 in Qinghai isolatesmight affect the antibody binding ability and virulence of the influenza virus.The presence of several antigenic site mutations in the Qinghai H3N2 isolates confirmed the evolution of circulating H3N2 strains.

Basic fibroblast growth factor protects against influenza A virus-induced acute lung injury by recruiting neutrophils

Influenza virus (IAV)infection is a major cause of severe respiratory illness that affects almost every country in the world.IAV infections result in respiratory illness and even acute lung injury and death,but the underlying mechanisms responsible for IAV pathogenesis have not yet been fully elucidated.In this study,the basic fibroblast growth factor 2 (FGF2)level was markedly increased in H1N1 virus-infected humans and mice.FGF2,which is predominately derived from epithelial cells,recruits and activates neutrophils via the FGFR2-PI3K-AKT-NFKB signaling pathway.FGF2 depletion or knockout exacerbated influenzaassociated disease by impairing neutrophil recruitment and activation.More importantly,administration of the recombinant FGF2 protein significantly aUeviated the severity of IAV-induced lung injury and promoted the survival of IAV-infected mice.Based on the results from experiments in which neutrophils were depleted and adoptively transferred,FGF2 protected mice against IAV , infection by recruiting neutrophils.Thus,FGF2 plays a critical role in preventing IAV-induced lung injury,and FGF2 is a promising potential therapeutic target during IAV infection.