Outbreaks of highly pathogenic avian influenza (HPAI) caused by H5N1 virus occurred in 2003 and 2004 in Korea and Japan. The H5N1 viruses isolated in both countries were genetically similar with > 99% identity in the nucleotide sequences of all eight RNA segments, indicating that they belong to genotype V and are distinct from the HPAI viruses prevalent in southeast Asia that belong to genotype Z. The virulence of the index isolate (A/chicken/Yamaguchi/7/2004) was studied in chickens and mice. Chickens intravenously or intranasally inoculated with the isolate died within 1 or 3 days of inoculation, respectively. In mice, although this virus replicated well in the lung without prior adaptation and spread to the brain, the dose lethal to 50% of the mice was 5 × 105 50% egg infectious doses (EID50), which is less pathogenic than the Hong Kong 1997 H5N1 viruses isolated from humans.
(Pathogenic Virus Section, Department of Infectious Diseases TEL +81-29-838-7760)
Reference:
Mase et al. (2005) Virology 332:167-176.
