Ecology of avian influenza viruses in migratory birds wintering within the Yangtze River wetlands

长江流域湿地越冬候鸟中禽流感病毒的生态学研究

Migratory birds are considered natural reservoirs of avian influenza A viruses(AIVs).To further our viral ecology knowledge and understand the subsequent risk posed by wild birds,we conducted a 4-year surveillance study of AIVs in the bird wintering wetlands of the Yangtze River,China.We collected over8000 samples and isolated 122 AIV strains.Analyses were then carried out with 108 novel sequenced genomes and data were deposited in GISAID and other public databases.The results showed that the Yangtze River wintering wetlands functioned as a mixing ground,where various subtypes of AIVs were detected harboring a high diversity of nucleotide sequences;moreover,a portion of AIV gene segments were persistent inter-seasonally.Phylogenetic incongruence presented complex reassortment events and distinct patterns among various subtypes.In addition,we observed that viral gene segments in wintering wetlands were closely related to known North American isolates,indicating that intercontinental gene flow occurred.Notably,highly pathogenic H5 and low pathogenic H9 viruses,which usually circulate in poultry,were found to have crossed the poultry/wild bird interface,with the viruses introduced to wintering birds.Overall,this study represented the largest AIV surveillance effort of wild birds within the Yangtze River wintering wetlands.Surveillance data highlighted the important role of wintering wild birds in the ecology of AIVs and may enable future early warnings of novel AIV emergence.

候鸟是A型禽流感病毒的自然宿主和储存库.为了深入了解我国候鸟禽流感病毒的流行规律及生态特点,本研究对长江流域越冬候鸟中的禽流感病毒进行长期监测,于2013~2017年间采集8000多份样本并分离出122株禽流感病毒.结果表明,长江流域越冬候鸟中禽流感病毒多样性丰富,监测期间发现8种HA亚型和8种NA亚型、18种HA-NA亚型组合.对其中108株病毒全基因组的分析表明,越冬地禽流感病毒基因组具有复杂的多样性,其中部分片段连续多个越冬季持续流行于候鸟中.进一步的系统发育分析表明越冬地禽流感病毒重配复杂且不同亚型重配模式截然不同.进化分析发现越冬候鸟病毒的一些基因片段与北美野鸟流行毒株高度相近,表明野鸟中禽流感病毒曾发生跨洲基因扩散.此外,家禽中流行的高致病H5和低致病H9禽流感病毒,跨越家禽/候鸟界面传播至野鸟中.综上,本研究是长江流域越冬候鸟大规模禽流感病毒监测的代表性工作,数年的监测数据凸显越冬候鸟在禽流感病毒生态分布中的重要作用,研究成果可为禽流感新毒株的突现提供早期预警.