title: Impact of embryonic passaging of H9N2 virus on pathogenicity and stability of HA1- amino acid sequence cleavage site.
abstract: BACKGROUND
  Highly virulent Avian Influenza viruses might arise from avirulent strains following viral passaging. This work aims at studying the impact of embryonic passaging of H9N2 on the stability of the HA1 amino acid sequence and its relatedness to pathogenicity.
  
  
  METHODS
  The original H9N2 virus was propagated for 3 consecutive passages in embryonated chicken eggs. Pathogenicity and amino acids sequences at the HA1 gene level of the original (P0), and the once (P1), twice (P2), and three times (P3) passaged viruses were compared.
  
  
  RESULTS
  The percent mortality significantly increased in embryos inoculated with P2 (86.7%) and P3 of H9N2 (100%) in comparison to P0 (0.0%) and P1 of H9N2 (46.1%) (P<0.05), while the density of propagated H9N2 declined with passaging. The R-S-S-R motif was stable at the HA1 cleavage site of P0, P1, P2, and P3 viruses. The similarity in the HA1 sequences among the differently passaged viruses ranged between 93.2 to 100%.
  
  
  CONCLUSIONS
  The pathogenicity increased significantly upon passaging in chicken embryos in spite of the presence of the same motif at the HA1 cleavage site. Further investigations will target the study of changes in the whole HA protein and of Neuraminidases that could be responsible for a higher pathogenicity.
authors.affiliation: Department of Animal and Veterinary Sciences, American University of Beirut, Beirut, Lebanon.
authors.forename: Houssam A
authors.initials: HA
authors.lastname: Shaib
authors.forename: Nelly
authors.initials: N
authors.lastname: Cochet
authors.forename: Thierry
authors.initials: T
authors.lastname: Ribeiro
authors.forename: Afif M
authors.initials: AM
authors.lastname: Abdel Nour
authors.forename: Georges
authors.initials: G
authors.lastname: Nemer
authors.forename: Elie K
authors.initials: EK
authors.lastname: Barbour
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002642:Chick Embryo; D002645:Chickens / Q000235:genetics / Q000276:immunology / Q000821:virology; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics*; D053127:Influenza A Virus, H9N2 Subtype / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity*; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity; D005585:Influenza in Birds / Q000503:physiopathology*
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus