| H9N2 avian influenza viruses have become endemic in China since mid-1990s.The infection of H9N2 virus is usually mild in nature,however,it may lead to higher mortality if coincides with or followed by a secondary infection.H9N2 viruses have evolved into distinct genotype in land-based poultry.A dominant genotype S(G57)of H9N2 viruses is circulating in country-wild chickens in China.S genotype emerged in 2007 and became predominant in 2010.H9N2 virus mainly cause outbreaks in poultry.The virus has expanded its host range to mammalian species.It was reported that they were isolated from domestic human and pigs in Hong Kong since 1998.H9N2 virus could also serve as gene donor for novel human avian influenza viruses including H5N1,H7N9 and H10N8.Hence,H9N2 virus is becoming a notable threat to public health.After H9N2 virus circulated in diferrent species of poultry,the virus may change its biologic characteristic under the pressure of environment and immune.Previous study indicated that some of vius of F98-like has the capacity of airborne transmission.However,There is no report about the the characteristic of transmission for S genotype virus.Epedimiologic date demonstrated that exposure to avian influenza virus infected poultry at live bird market(LBM)has been implicated as the main risk factor for human infection and poultry are considered to be the virus reservoir with an important role in the transmission for multiple subtype influenza viruses.However,despite multiple lineages and genotypes that were detected by previous studies,the evolution of pathogenicity of the H9N2 virus in China is unclear.Increasing such knowledge would help us better prevent and control H9N2 as well as other future potentially threatening viruses from spreading across China.The objectives of this study were to determine the epidemiology of avian influenza virus in LBM,phylogenetic analysis of genome and pathogenicity of avian influenza A H9N2 virus that circulated in China.1.Epidemiological survey of avian influenza in Jiangsu Province during 2014-2016Etiological surveillance of avian influenza was conducted in several live poultry markets in Jiangsu Province from December 2014 to November 2015,and a total of 42 avian influenza viruses were isolated from 900 swab samples of 76 different poultry flocks.The isolates belonged to 8 HA subtypes involving H1?H3,H4,H5,H6,H7,H9 and H11.The average virus positive rate of the total specimens and flocks were 4.67%and 23.7%,respectively.In particular,highly pathogenic H5 subtype avian influenza virus ranked the highest isolation rate with 1.1%,accounting for 23.8%of all the positive strains.The second-most viruses were of the low pathogenicity H9 subtype with an isolation rate of 0.67%.Other subtypes of low pathogenic subtypes containing H1,H3,H4,H6 and H11 all owned relatively low positive rates,and they were exclusively isolated from waterfowls.As for the investigated hosts,ducks had the highest isolation rate of 10.6%while chickens bearing a positive rate of 3.25%ranked the second top.These above results indicated the diversity of avian influenza viruses in live poultry markets.Chickens were the predominant infectious hosts of H5,H7 and H9 subtype viruses,whereas ducks harbored all the remaining subtype viruses except H7,especially of H3,H4,H6 and H11.In addition,H5,H7 and H9 subtype viruses mainly appeared in autumn and winter.Therefore,live poultry markets were critical places accommodating different subtypes of avian influenza viruses,and ducks were the most important reservoir.So,it was of crucial significance to strengthen the surveillance and management of live poultry markets.During 2015 to 2016,a total of 64 H9 subtype avian influenza viruses were isolated from the clinical samples,H9 subtype was still prevalent in the East China currently.2.The Genetic Variation of H9N2 Avian Influenza Virus in Eastern China71 H9N2 viruses was isolated from healthy poultry at LBM or tissue samples collected in Eastern China during 2015 to 2016.All the viruses had a characteristic of low-pathogenic avian influenza virus(LPAI).Their HA and NA gene were amplified and sequenced.Phylogenetic analysis demonstrated that HA and NA gene of these viruses shared 86.7%-94.3%nucleotide sequence identity with that of H9N2 viruses isolated in 2007-2009,94.6%-97.8%with that of viruses in 2010-2014.Among the viruses in this study 95.1%-98.9%identity was found.Analysis on genome sequences of these viruses indicated that they all belong to the dominant S genotype.Compared with the viruses isolated before 2013,the viruses have some predominant mutations in each gene,including HA mutation Q226L,PB2 mutations:I293V,T598V and L648V,PB1 mutations:K25N,K363R and T257A,PA mutation K356R,and so on.These adaptation mutations may contribute to enhanced viral polymerase activity,the efficient virus replication in new host species.In addition,PB2 E627K,a well-known mammalian adaptive marker,was found in two avian-origin H9N2 viruses.Eight genes of H9N2 viruses evolved chronologically with deduced genetic diversity(almost only one genotype of S circulating in poultry in Eastern China).But adaption mutation made viruses having enhanced pathogenicity.It indicated that more intensive measure to survey these molecular marker to avoid new pandemic outbreak is necessary.3.Pathogenicity and Propagation Characteristic of H9N2 Subtype Avian Influenza Virus in Different YearsIn order to explore the pathogenicity and biological characteristics of rapid spreading of H9N2 virus on chickens,the six strains AH320/2016,SDKD1/2015,TM118/2014,WJ57/2012,HeN86/2008,SH7/2001 were chosen to infect the SPF chicken in transmission experiment.In this study SH7 virus has been proved with airborne transmission as a positive control.Experimental results show that late strain SDKD1,AH320,TM118,compared with the early strain WJ57 and HeN86,distributed in the multiple tissue organs detected,with longer survival time,higher viral load.Aerosol transmission test showed that compared with early strain HeN86,WJ57 capable of aerosol transmission in one of three chickens,but late strain SDKD1 and AH320 can transmit by droplet from 5 day to 9 day post infection with high viral shedding and seroconversion.Recent virus has airborne transmissibility which will be helpful to bind to the human-like receptor and has potential in the cross-species transmission. |
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