title: A low pathogenic H5N2 influenza virus isolated in Taiwan acquired high pathogenicity by consecutive passages in chickens.
abstract: H5N2 viruses were isolated from cloacal swab samples of apparently healthy chickens in Taiwan in 2003 and 2008 during surveillance of avian influenza. Each of the viruses was eradicated by stamping out. The official diagnosis report indicated that the Intravenous Pathogenicity Indexes (IVPIs) of the isolates were 0.00 and 0.89, respectively, indicating that these were low pathogenic strains, although the hemagglutinin of the strain isolated in 2008 (Taiwan08) had multibasic amino acid residues at the cleavage site (PQRKKR/G). In the present study, these H5N2 viruses were assessed for their intravenous and intranasal pathogenicity for chickens. It was examined whether Taiwan08 acquires pathogenicity through consecutive passages in chickens. Intravenous pathogenicity of Taiwan08 depended upon the age of the chickens used for the IVPI test; all of the eight-week-old chickens intravenously inoculated with Taiwan08 showed clinical signs but survived for ten days post inoculation (IVPI=0.68), whereas all the six-week-old chickens died (IVPI=1.86). Taiwan08-P8, which were passaged in chickens for eight times, killed all the eight-week-old chickens (IVPI=2.36). The four-week-old chickens died after intranasal inoculation of Taiwan08-P8, indicating that Taiwan08 must have become highly pathogenic during circulation in chicken flocks. These results emphasize the importance of a stamping out policy for avian influenza even if the IVPI of the causal virus is low.
authors.affiliation: 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: Ming-Chu
authors.initials: MC
authors.lastname: Cheng
authors.forename: Hiromi
authors.initials: H
authors.lastname: Yoshida
authors.forename: Mayumi
authors.initials: M
authors.lastname: Endo
authors.forename: Shu-Hwae
authors.initials: SH
authors.lastname: Lee
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Okamatsu
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sakoda
authors.forename: Ching-Ho
authors.initials: CH
authors.lastname: Wang
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kida
mesh_terms: D000367:Age Factors; D000595:Amino Acid Sequence; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002645:Chickens; D016679:Genome, Viral; D053124:Influenza A Virus, H5N1 Subtype / Q000235:genetics / Q000472:pathogenicity*; D005585:Influenza in Birds / Q000235:genetics / Q000821:virology*; D009154:Mutation; D012367:RNA, Viral / Q000737:chemistry / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D013624:Taiwan; D014774:Virulence
chemical_list: D000914:Antibodies, Viral; D012367:RNA, Viral