title: H9N2 influenza virus acquires intravenous pathogenicity on the introduction of a pair of di-basic amino acid residues at the cleavage site of the hemagglutinin and consecutive passages in chickens.
abstract: BACKGROUND
  Outbreaks of avian influenza (AI) caused by infection with low pathogenic H9N2 viruses have occurred in poultry, resulting in serious economic losses in Asia and the Middle East. It has been difficult to eradicate the H9N2 virus because of its low pathogenicity, frequently causing in apparent infection. It is important for the control of AI to assess whether the H9N2 virus acquires pathogenicity as H5 and H7 viruses. In the present study, we investigated whether a non-pathogenic H9N2 virus, A/chicken/Yokohama/aq-55/2001 (Y55) (H9N2), acquires pathogenicity in chickens when a pair of di-basic amino acid residues is introduced at the cleavage site of its HA molecule.
  
  
  RESULTS
  rgY55sub (H9N2), which had four basic amino acid residues at the HA cleavage site, replicated in MDCK cells in the absence of trypsin after six consecutive passages in the air sacs of chicks, and acquired intravenous pathogenicity to chicken after four additional passages. More than 75% of chickens inoculated intravenously with the passaged virus, rgY55sub-P10 (H9N2), died, indicating that it is pathogenic comparable to that of highly pathogenic avian influenza viruses (HPAIVs) defined by World Organization for Animal Health (OIE). The chickens inoculated with the virus via the intranasal route, however, survived without showing any clinical signs. On the other hand, an avirulent H5N1 strain, A/duck/Hokkaido/Vac-1/2004 (Vac1) (H5N1), acquired intranasal pathogenicity after a pair of di-basic amino acid residues was introduced into the cleavage site of the HA, followed by two passages by air sac inoculation in chicks.
  
  
  CONCLUSIONS
  The present results demonstrate that an H9N2 virus has the potential to acquire intravenous pathogenicity in chickens although the morbidity via the nasal route of infection is lower than that of H5N1 HPAIV.
authors.affiliation: Laboratory of Microbiology, Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido 060-0818, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Soda
authors.forename: Shingo
authors.initials: S
authors.lastname: Asakura
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Okamatsu
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sakoda
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kida
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002645:Chickens; D004285:Dogs; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D053124:Influenza A Virus, H5N1 Subtype / Q000472:pathogenicity / Q000502:physiology; D053127:Influenza A Virus, H9N2 Subtype / Q000737:chemistry / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology; D005585:Influenza in Birds / Q000821:virology*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D011201:Poultry Diseases / Q000821:virology*; D011499:Protein Processing, Post-Translational; D012692:Serial Passage
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus