title: Emergence and development of H7N9 influenza viruses in China.
abstract: The occurrence of human infections with avian H7N9 viruses since 2013 demonstrates the continuing pandemic threat posed by the current influenza ecosystem in China. Influenza surveillance and phylogenetic analyses showed that these viruses were generated by multiple interspecies transmissions and reassortments among the viruses resident in domestic ducks and the H9N2 viruses enzootic in chickens. A large population of domestic ducks hosting diverse influenza viruses provided the precondition for these events to occur, while acquiring internal genes from enzootic H9N2 influenza viruses in chickens promoted the spread of these viruses. Human infections effectively act as sentinels, reflecting the intensity of the activity of these viruses in poultry.
authors.affiliation: Joint Influenza Research Centre (SUMC/HKU), Shantou University Medical College, Shantou 515041, China; State Key Laboratory of Emerging Infectious Diseases (HKU-Shenzhen Branch), Shenzhen Third People's Hospital, Shenzhen 518112, China; Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China. Electronic address: zhuhch@hku.hk.
authors.forename: Huachen
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China.
authors.forename: Tommy Tsan-Yuk
authors.initials: TT
authors.lastname: Lam
authors.affiliation: Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China.
authors.forename: David Keith
authors.initials: DK
authors.lastname: Smith
authors.affiliation: Joint Influenza Research Centre (SUMC/HKU), Shantou University Medical College, Shantou 515041, China; State Key Laboratory of Emerging Infectious Diseases (HKU-Shenzhen Branch), Shenzhen Third People's Hospital, Shenzhen 518112, China; Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Guan
mesh_terms: D000818:Animals; D002645:Chickens; D002681:China / Q000453:epidemiology; D021821:Communicable Diseases, Emerging; D004372:Ducks; D019143:Evolution, Molecular; D005838:Genotype; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D005585:Influenza in Birds / Q000453:epidemiology / Q000635:transmission / Q000821:virology; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission / Q000821:virology*; D010802:Phylogeny; D016865:Reassortant Viruses; D012307:Risk Factors