Sequence Analysis And Pathogenicity Study Of A Novel Highly Pathogenic H7N9 Influenza Virus

The first case of human infection H7N9 avian influenza virus was appeared in March 2013 in china,which was a low-pathogenic avian influenza virus(LPAIV)and was subsequently found in the flocks of birds.As of 30 st April 2017,1418 human cases and 572 deaths have been confirmed.Guangdong Provincial Center for Disease Control and Prevention found that two cases of human infection with H7N9 virus in January 2017,isolated from the virus hemagglutinin(HA)cleavage site position inserted four amino acids KRTA,that was PKGR/G mutation PKRKRTA/G,suggesting that the virus had a molecular characterization of highly pathogenicity to avian.So far,three high incidences of highly pathogenic H7N9 in poultry were reported by the Ministry of Agriculture,in Hunan Yongzhou(March 19,2017),Hebei Xingtai(April 28,2017)and Henan Pingdingshan(2017 Year on May 3),respectively.Three outbreaks resulted in the death of a large number of laying hens,causing huge economic losses.Therefore,sequence analysis and pathogenicity study of a novel highly pathogenic H7N9 influenza virus,as soon as possible.Firstly,in this study,128 strains of H7N9 subtype influenza viruses isolated from 2013 to 2017 were retrospectively analyzed.Seven strains of H7N9 subtype avian influenza virus with high pathogenic molecular characteristics were identified,HA gene clea vage site was PKGKRTAR/G and PKRKRTAR/G,the difference between these two manifestations is caused by a nucleotide mutation(G/A)and then lead to an amino acid(G/R)changes.Next,the H7N9 subtype influenza virus sequence were collected from the genome a nd the sequences in the Gen Bank and GISAID databases were used to analyze the genetic evolution characteristics of newly emerging highly pathogenic H7N9 subtype influenza virus.Then,according to the phylogenetic tree analysis results of HA gene,three strains of H7N9 virus were selected in combination with the basic amino acid sequence of HA gene.Pathogenicity of viruses to SPF chicken,BALB/c mice and influenza negative duck were performed.(PKGR/G,referred to as SW154),A/C hicken/Heyuan/16876/2016(PKGKRTAR/G,referred to as 16876),A/C hicken/Huizhou/HZ-3/2016(PKRKRTAR/G,referred to as HZ-3).The IVPI value of SW154 virus,16876 virus,HZ-3 virus were 0,2.92 and 3.0,respectively,indicating that the 16876 and HZ-3 viruses were highly pathogenic avian influenza viruses.In the SPF chicken pathogenicity test,16876 and HZ-3 virus infect group and contact group of chickens can be 100% lethal,proof of these two types of viruses on the chicken's high pathogenicity,high lethalityand strong ability to spread;While SW154 virus infect group,contact group and negative control group of chickens were not found abnormal.Compared with the classical attenuated strain SW154,the new H7N9 virus 16876 and HZ-3 strains were pathogenic to BALB/c mice,and caught 10-20% of mice to die.In view of the current grim situation,it is urgent to strengthen the epidemiological surveillance of these newly emerging highly pathogenic H7N9 viruses and to further develop pathogenicity-related studies and the development of targeted vaccines.