title: Infectivity and Transmissibility of Avian H9N2 Influenza Viruses in Pigs.
abstract: The H9N2 influenza viruses that are enzootic in terrestrial poultry in China pose a persistent pandemic threat to humans. To investigate whether the continuous circulation and adaptation of these viruses in terrestrial poultry increased their infectivity to pigs, we conducted a serological survey in pig herds with H9N2 viruses selected from the aquatic avian gene pool (Y439 lineage) and the enzootic terrestrial poultry viruses (G1 and Y280 lineages). We also compared the infectivity and transmissibility of these viruses in pigs. It was found that more than 15% of the pigs sampled from 2010 to 2012 in southern China were seropositive to either G1 or Y280 lineage viruses, but none of the sera were positive to the H9 viruses from the Y439 lineage. Viruses of the G1 and Y280 lineages were able to infect experimental pigs, with detectable nasal shedding of the viruses and seroconversion, whereas viruses of the Y439 lineage did not cause a productive infection in pigs. Thus, adaptation and prevalence in terrestrial poultry could lead to interspecies transmission of H9N2 viruses from birds to pigs. Although H9N2 viruses do not appear to be continuously transmissible among pigs, repeated introductions of H9 viruses to pigs naturally increase the risk of generating mammalian-adapted or reassorted variants that are potentially infectious to humans. This study highlights the importance of monitoring the activity of H9N2 viruses in terrestrial poultry and pigs.
  
  
  OBJECTIVE
  H9N2 subtype of influenza viruses has repeatedly been introduced into mammalian hosts, including humans and pigs, so awareness of their activity and evolution is important for influenza pandemic preparedness. However, since H9N2 viruses usually cause mild or even asymptomatic infections in mammalian hosts, they may be overlooked in influenza surveillance. Here, we found that the H9N2 viruses established in terrestrial poultry had higher infectivity in pigs than those from aquatic birds, which suggests that adaptation of the H9N2 viruses in terrestrial poultry might have increased the infectivity of the virus to mammals. Therefore, monitoring the prevalence and evolution of H9 viruses prevalent in terrestrial birds and conducting risk assessment of their threat to mammals are critical for evaluating the pandemic potential of this virus.
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China State Key Laboratory of Emerging Infectious Diseases and Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China.
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China.
authors.forename: Maocai
authors.initials: M
authors.lastname: Wu
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China.
authors.forename: Wenshan
authors.initials: W
authors.lastname: Hong
authors.affiliation: Department of Microbiology, Guangxi Medical University, Nanning, China.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Fan
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China.
authors.forename: Rirong
authors.initials: R
authors.lastname: Chen
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China.
authors.forename: Zuoyi
authors.initials: Z
authors.lastname: Zheng
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zeng
authors.affiliation: Guangdong Laboratory Animals Monitoring Institute, Guangzhou, China.
authors.forename: Ren
authors.initials: R
authors.lastname: Huang
authors.affiliation: Guangdong Laboratory Animals Monitoring Institute, Guangzhou, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Emerging Infectious Diseases and 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: State Key Laboratory of Emerging Infectious Diseases and Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China.
authors.forename: David K
authors.initials: DK
authors.lastname: Smith
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China State Key Laboratory of Emerging Infectious Diseases and Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China zhuhch@hku.hk yguan@hku.hk.
authors.forename: Huachen
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Joint Influenza Research Center, Shantou University Medical College, Shantou, China State Key Laboratory of Emerging Infectious Diseases and Centre of Influenza Research, School of Public Health, The University of Hong Kong, Hong Kong, China Department of Microbiology, Guangxi Medical University, Nanning, China zhuhch@hku.hk yguan@hku.hk.
authors.forename: Yi
authors.initials: Y
authors.lastname: Guan
mesh_terms: D000818:Animals; D002642:Chick Embryo; D002681:China; D006801:Humans; D053127:Influenza A Virus, H9N2 Subtype / Q000472:pathogenicity*; D005585:Influenza in Birds / Q000635:transmission* / Q000821:virology; D007251:Influenza, Human / Q000821:virology; D009976:Orthomyxoviridae Infections / Q000635:transmission* / Q000662:veterinary* / Q000821:virology; D011200:Poultry / Q000821:virology; D011201:Poultry Diseases / Q000635:transmission* / Q000821:virology; D013552:Swine; D013553:Swine Diseases / Q000821:virology*