title: Rapid emergence of a virulent PB2 E627K variant during adaptation of highly pathogenic avian influenza H7N7 virus to mice.
abstract: BACKGROUND
  Highly pathogenic avian influenza (HPAI) viruses pose a potential human health threat as they can be transmitted directly from infected poultry to humans. During a large outbreak of HPAI H7N7 virus among poultry in The Netherlands in 2003, bird to human transmission was confirmed in 89 cases, of which one had a fatal outcome.
  
  
  METHODS
  To identify genetic determinants of virulence in a mammalian host, we passaged an avian H7N7/03 outbreak isolate in mouse lungs and evaluated the phenotype of the mouse-adapted variant in animal models and in vitro.
  
  
  RESULTS
  Three passages in mouse lungs were sufficient to select a variant that was highly virulent in mice. The virus had a MLD50 that was >4.3 logs lower than that of its non-lethal parental virus. Sequence analysis revealed a single mutation at position 627 in PB2, where the glutamic acid was changed to a lysine (E627K). The mouse-adapted virus has this mutation in common with the fatal human case isolate. The virus remained highly pathogenic for chickens after its passage in mice. In ferrets, the mouse-adapted virus induced more severe disease, replicated to higher titers in the lower respiratory tract and spread more efficiently to systemic organs compared with the parental virus. In vitro, the PB2 E627K mutation had a promoting effect on virus propagation in mammalian, but not in avian cells.
  
  
  CONCLUSIONS
  Our results show that the E627K mutation in PB2 alone can be sufficient to convert an HPAI H7N7 virus of low virulence to a variant causing severe disease in mice and ferrets. The rapid emergence of the PB2 E627K mutant during mouse adaptation and its pathogenicity in ferrets emphasize the potential risk of HPAI H7N7 viruses for human health.
authors.affiliation: Central Veterinary Institute of Wageningen UR, Lelystad, Netherlands. Lisette.cornelissen@wur.nl.
authors.forename: Rineke M C
authors.initials: RM
authors.lastname: de Jong
authors.forename: Norbert
authors.initials: N
authors.lastname: Stockhofe-Zurwieden
authors.forename: Eline S
authors.initials: ES
authors.lastname: Verheij
authors.forename: Els A
authors.initials: EA
authors.lastname: de Boer-Luijtze
authors.forename: Saskia J M
authors.initials: SJ
authors.lastname: Ruiter
authors.forename: Olav S
authors.initials: OS
authors.lastname: de Leeuw
authors.forename: Lisette A H M
authors.initials: LA
authors.lastname: Cornelissen
mesh_terms: D000220:Adaptation, Biological; D000825:Animal Structures / Q000473:pathology / Q000821:virology; D000818:Animals; D002645:Chickens; D004195:Disease Models, Animal; D005260:Female; D005289:Ferrets; D053126:Influenza A Virus, H7N7 Subtype / Q000235:genetics* / Q000302:isolation & purification*; D005585:Influenza in Birds / Q000821:virology; D007928:Lethal Dose 50; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D020125:Mutation, Missense; D009976:Orthomyxoviridae Infections / Q000473:pathology / Q000821:virology; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics*; D016019:Survival Analysis; D014764:Viral Proteins / Q000235:genetics*; D014774:Virulence
chemical_list: C057027:PB2 protein, Influenzavirus A; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase