| New cases infected by avian influenza viruses(AIVs)such as H5N1,H9N2,H7N9,H6N1,H10N8,H5N6,and H7N4 have been reported in recent years,which poses a great threat to humans and raises broadly public health concerns.The number of birds and live poultry consumption pattern in China have created an avenue for the reassortment of AIVs horder to assess the risk of human infected AIVs due to occupational exposure and to understand the molecular characteristics of cross species transmission of H7N9 AIVs.A prospective serological study from seven areas in China was conducted from December 2014 to April 2016 on basis of surveillance network.Blood samples were collected before and after the epidemic season and questionaires were administered to gather related information.Antibody titers against AIVs viz H5N1,H5N6,H6N1,H6N6,H7N9,H9N2 and H10N8 were tested from the serum samples using both hemagglutination-inhibition(HI)and micro-neutralization assays(MN).A cross-sectional survey for single sample and a cohort survey for multiple joined participants were carried out during this study.Risk factors for positive participants were analyzed by logistic regression.Furthermore,240 whole genome sequences including the newly isolated 35 H7N9 strains were carefully observed for their sequence identity and systematically analyzed for their evolutionary characteristics.A total of 1406 participants from December 2014 to April 2016 were enrolled in this study,covering a cross-sectional survey for 755 and a cohort survey for 651 individuals.The results from seropositive ratios revealed that cross-sectional survey has the highest seroprevelence rate in H9N2(10.9%),followed by H7N9(3.3%),H5N1(0.5%for H5N1-SH199,and 1.9%for H5N1-SC29),H5N6(2.0%)and H6N1(1.7%)while no H10N8 seropositve participant was detected in the enrolled cohort.The cohort survey in the study indicated that a high seroconversion in H9N2(8.4%),followed by H7N9(2.2%)within two years.The highest seroconversion of H9N2 was in Shandong(21.9%)and H7N9 was observed in Yangzi River region,including Jiangsu(8.4%)and Shanghai(8.3%).Regression analysis of the risk factors showed that the poultry exposure-related factors "years of occupation" and "exposure to ducks/ill or dead poultry",etc.,were associated with seroprevalence of different AIVs.Notably,virus isolation rate in the poultry was an independent factor for the seroprevalence of H7N9 and H9N2 in the corresponding poultry-contact workers.HP-H7N9 and LP-H7N9 has spread virtually throughout China and underwent dynamic reassortment with different subtypes(H7N9/H9N2 and H6Ny)and lineages(Yangtze and Pearl River Delta lineages),resulting in a total of 36 and three major genotypes(G1/G3/G11).The HP-H7N9 likely evolved from G1 LP-H7N9 by the insertion of a "KRTA" motif at the cleavage site(CS),then evolved into fifteen genotypes with four different CS motifs including PKGKRTAR/G,PKGKRIAR/G,PKRKRAAR/G and PKRKRTAR/G.Approximately 46%(28/61)of HP strains belonged to G3.Importantly,neuraminidase(NA)inhibitor resistance(R292K in NA)and mammalian adaptation(eg.E627K and D701N in PB2)mutations were found in a few non-human-derived HP-H7N9 strains.In summary,the proportional ratios against different AIVs were tested among poultry workers,and mammals-adaptive and drug resistance strains produced by reassortment and mutation were systematically analyzed,suggesting the cross-species transmission possibilities from AIVs to humans.Surveillance of poultry related occupation should be enforced and used as a tool to efficiently prevent and eliminate the threats of AIVs to public health. |
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