Prevalence,Evolution,and Spread Of Avian Influenza Viruses In Migratory Anatidae

Avian influenza virus(AIV)is a pathogen that can cause contagious respiratory diseases in avian hosts.AIV has a wide range of hosts,including various types of poultry,wild birds,marine mammals,terrestrial mammals,and even humans,posing a serious threat to poultry farming,wildlife health,and public health safety.Wild waterfowl,especially the order Anseriformes,are considered natural hosts and natural reservoirs of AIV.Their migratory activities play an important role in the transboundary transmission of AIV.Based on the epidemiological surveillance of AIV,this study continues to investigate the background of AIV carried by migratory birds in the middle and lower reaches of the Yangtze River and Heilongjiang Province.On the basis of the diversity,epidemiological patterns and distribution characteristics of AIV in the complex ecosystem of the middle and lower reaches of the Yangtze River in China,the genetic evolution patterns and biological characteristics of different subtypes of AIV viruses were analyzed by using molecular biology methods.Furthermore,the molecular epidemiology of important representative isolates was combined with the migration pattern of wild Anatidae,revealing two important routes for wild Anatidae carrying H5 subtype AIV in different directions to spread virus to the middle and lower reaches of the Yangtze River.Those results provide critical data for the cross-border transmission,early warning,and prevention and control of AIV.1.Epidemiological surveillance of avian influenza virusBetween November 2018 and October 2022,a total of 31526 wild bird related samples were collected from the important habitats for migratory waterfowl along the East AsiaAustralia and Central Asia migratory flyways in the middle and lower reaches of the Yangtze River and Heilongjiang Province,and 258 AIVs were isolated,with an overall isolation rate of0.82%,which is within the normal range for wild birds.This study found that the AIV isolation rate was significantly higher during the autumn migration period than during the spring migration period,and the AIV isolation rate was higher in wintering sites than in stopover site.AIV isolates included 17 combinations of 7 HA subtypes and 6 NA subtypes.The dominant HA subtypes were H5 and H4,and the dominant NA subtypes were N1,N8,and N6,with the dominant HA and NA combinations changing in different years.The highest AIV isolation rate and subtype diversity were found in wild Anatidae.These results indicate that wild Anatidae are susceptible species for AIV,and can be used as important indicator species for monitoring AIV in the middle and lower reaches of the Yangtze River.2.Genetic evolutionary analyses of representative AIV isolatesA total of 186 strains of AIV isolates were selected as representative strains for whole genome amplification and genetic evolutionary analysis.The results showed that there was rich genetic diversity of AIV gene segments carried by wild birds in the middle and lower reaches of the Yangtze River and Heilongjiang Province.Some gene segments existed continuously in wild bird populations,while there was complex genetic recombination among different subtypes of AIV.The H5 subtype of AIV showed a high genetic diversity across the whole genome,indicating a complex origin source.Wild Anatidae was the important drivers for genetic exchanges of AIV among the middle and lower reaches of the Yangtze River,Heilongjiang Province,Japan,South Korea,Mongolia,and Russia.Moreover,North American-origin AIV was frequently detected in the middle and lower reaches of the Yangtze River and Heilongjiang Province,indicating the continuous occurrence of long-distance intercontinental transmission.3.The migration of wild Anatidae and the transboundary spread of H5 subtype avian influenza virusH5 subtype AIV was selected and various species of Anatidae were continuously tracked by satellite.Based on the satellite tracking results of wild Anatidae,three migration routes for overwintering birds in the middle and lower reaches of the Yangtze River were identified: the Central Asian inland migration route,the East Asian inland migration route,and the East Asian coastal migration route.Combined with AIV molecular data,we found that the temporal and spatial dynamic of the transboundary transmission of the clade 2.3.4.4b H5N8 subtype HPAIV in the autumn of 2020 showed highly consistent pattern with the autumn migration of swans along the Central Asian inland migration route,indicating that swans could be a key sentinel species for monitoring HPAIV entering the middle and lower reaches of the Yangtze River along the Central Asian inland migration route.In the East Asian coastal migration route,the migration patterns of wild Anatidae are highly consistent with the dynamics of North American-origin H5 subtype AIV entering East Asia,indicating that the migration of wild birds(Anatidae)are closely related to the intercontinental transmission of North American-origin H5 subtype AIV across the Bering Strait to East Asia.