A Low Pathogenic H5N2 Influenza Virus Isolated in Taiwan Acquired High Pathogenicity by Consecutive Passages in Chickens

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  • SODA Kosuke
    Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University
  • CHENG Ming-Chu
    Animal Health Research Institute, Council of Agriculture Department of Veterinary Medicine, National Taiwan University
  • YOSHIDA Hiromi
    Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University
  • ENDO Mayumi
    Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University
  • LEE Shu-Hwae
    Animal Health Research Institute, Council of Agriculture
  • OKAMATSU Masatoshi
    Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University
  • SAKODA Yoshihiro
    Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University
  • WANG Ching-Ho
    Department of Veterinary Medicine, National Taiwan University
  • KIDA Hiroshi
    Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University Research Center for Zoonosis Control, Hokkaido University SORST, Japan Science and Technology Agency (JST)

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  • Virology: A low pathogenic H5N2 influenza virus isolated in Taiwan acquired high pathogenicity by consecutive passages in chickens

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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.<br>

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