title: Two Outbreak Sources of Influenza A (H7N9) Viruses Have Been Established in China.
abstract: Due to enzootic infections in poultry and persistent human infections in China, influenza A (H7N9) virus has remained a public health threat. The Yangtze River Delta region, which is located in eastern China, is well recognized as the original source for H7N9 outbreaks. Based on the evolutionary analysis of H7N9 viruses from all three outbreak waves since 2013, we identified the Pearl River Delta region as an additional H7N9 outbreak source. H7N9 viruses are repeatedly introduced from these two sources to the other areas, and the persistent circulation of H7N9 viruses occurs in poultry, causing continuous outbreak waves. Poultry movements may contribute to the geographic expansion of the virus. In addition, the AnH1 genotype, which was predominant during wave 1, was replaced by JS537, JS18828, and AnH1887 genotypes during waves 2 and 3. The establishment of a new source and the continuous evolution of the virus hamper the elimination of H7N9 viruses, thus posing a long-term threat of H7N9 infection in humans. Therefore, both surveillance of H7N9 viruses in humans and poultry and supervision of poultry movements should be strengthened.
  
  
  
  Since its occurrence in humans in eastern China in spring 2013, the avian H7N9 viruses have been demonstrating the continuing pandemic threat posed by the current influenza ecosystem in China. As the viruses are silently circulated in poultry, with potentially severe outcomes in humans, H7N9 virus activity in humans in China is very important to understand. In this study, we identified a newly emerged H7N9 outbreak source in the Pearl River Delta region. Both sources in the Yangtze River Delta region and the Pearl River Delta region have been established and found to be responsible for the H7N9 outbreaks in mainland China.
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Dayan
authors.initials: D
authors.lastname: Wang
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Wenfei
authors.initials: W
authors.lastname: Zhu
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Shumei
authors.initials: S
authors.lastname: Zou
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Bo
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Rongbao
authors.initials: R
authors.lastname: Gao
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Jie
authors.initials: J
authors.lastname: Dong
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Weijuan
authors.initials: W
authors.lastname: Huang
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Guo
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Zi
authors.initials: Z
authors.lastname: Li
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhao
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Li
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Li
authors.initials: L
authors.lastname: Xin
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Jianfang
authors.initials: J
authors.lastname: Zhou
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Tao
authors.initials: T
authors.lastname: Chen
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Libo
authors.initials: L
authors.lastname: Dong
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Hejiang
authors.initials: H
authors.lastname: Wei
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Xiyan
authors.initials: X
authors.lastname: Li
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Liqi
authors.initials: L
authors.lastname: Liu
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Jing
authors.initials: J
authors.lastname: Tang
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Lan
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China.
authors.forename: Jing
authors.initials: J
authors.lastname: Yang
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention; Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, People's Republic of China yshu@cnic.org.cn.
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
mesh_terms: D000818:Animals; D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks; D019143:Evolution, Molecular; D005814:Genes, Viral; D005838:Genotype; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D005585:Influenza in Birds / Q000453:epidemiology* / Q000821:virology; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D009439:Neuraminidase / Q000235:genetics; D010802:Phylogeny; D011200:Poultry; D016865:Reassortant Viruses; D045483:Rivers
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; C109963:hemagglutinin, avian influenza A virus; D009439:Neuraminidase