title: Imported pigs may have introduced the first classical swine influenza viruses into Mainland China.
abstract: OBJECTIVE
  The first classical swine influenza A H1N1 viruses were isolated in Mainland China in 1991. To aid surveillance of swine influenza viruses as part of pandemic preparedness, we sought to identify their origin.
  
  
  METHODS
  We sequenced and phylogenically analyzed 19 swine influenza viruses isolated in 1991 and 1992 in China and compared them with viruses isolated from other regions during the same period.
  
  
  RESULTS
  All 19 swine influenza viruses analyzed in our study shared the highest similarity with the classical swine influenza virus A/Swine/Maryland/23239/1991 (H1N1). Phylogenetic trees of eight segmented genes exhibited similar topology, with all segments in the cluster of classical swine influenza viruses. In addition, antigenic analysis also indicated that the tested isolated were related to classical swine influenza isolates.
  
  
  CONCLUSIONS
  Classical swine H1N1 influenza viruses were predominant in Beijing pig herds during this period. Since both antibody and virus detections did not indicate the presence of CS H1N1 before 1991 in Mainland China, we combined with the data on pigs imported to and exported from China and concluded that these viruses might spread to China via pigs imported from North America and that they could affect the genetic evolution and transmission dynamics of swine influenza viruses in Hong Kong.
authors.affiliation: Chinese National Influenza Center, National Institute for Viral Disease Control and Prevention, Key Laboratory of Surveillance and Early-warning on Infectious Disease, China CDC, Key Laboratory for Medical Virology, Ministry of Health, 155 Changbai Road, Beijing 102206, PR China.
authors.forename: Wenfei
authors.initials: W
authors.lastname: Zhu
authors.forename: Shuai
authors.initials: S
authors.lastname: Yang
authors.forename: Yuanji
authors.initials: Y
authors.lastname: Guo
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
authors.forename: Tian
authors.initials: T
authors.lastname: Bai
authors.forename: Zaijiang
authors.initials: Z
authors.lastname: Yu
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Li
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Junfeng
authors.initials: J
authors.lastname: Guo
authors.forename: Dayan
authors.initials: D
authors.lastname: Wang
authors.forename: Rongbao
authors.initials: R
authors.lastname: Gao
authors.forename: Libo
authors.initials: L
authors.lastname: Dong
authors.forename: Shumei
authors.initials: S
authors.lastname: Zou
authors.forename: Zi
authors.initials: Z
authors.lastname: Li
authors.forename: Min
authors.initials: M
authors.lastname: Wang
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
mesh_terms: D000818:Animals; D002642:Chick Embryo; D002681:China / Q000453:epidemiology; D005814:Genes, Viral; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000235:genetics* / Q000276:immunology; D009976:Orthomyxoviridae Infections / Q000662:veterinary*; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013552:Swine / Q000821:virology*; D013553:Swine Diseases / Q000453:epidemiology / Q000276:immunology / Q000635:transmission*