Characterization of the low-pathogenic H5N1 avian influenza virus in South Korea

The low-pathogenic avian influenza (LPAI) virus can serve as a progenitor of the highly pathogenic avian influenza virus, so it is important to monitor the LPAI virus as well as the highly pathogenic avian influenza virus. The Korean LPAI H5N1 virus, A/wild duck/Kr/CSM4-12/09 (H5N1) [Wd/CSM4-12/09], was first isolated from feces of the wild duck in South Korea. Genetic analysis showed that 7 genes of Wd/CSM 4-12/09 clustered in eastern Asia and that the neuraminidase (NA) gene of this isolate was closely related to European LPAI viruses. The Korean LPAI H5N1 virus has the highest similarity with the Japanese LPAI H5N1 virus, A/mallard/Hokkaido/24/09 (H5N1), in 6 genes [polymerase basic protein 2 (PB2), polymerase basic protein 1 (PB1), polymerase acidic protein (PA), hemagglutinin (HA), NA, and nonstructural (NS) genes]. The Korean LPAI H5N1 virus did not replicate in experimentally infected chickens, whereas it replicated in ducks and mice without preadaptation. This study shows that the first Korean LPAI H5N1 reassortment, which occurred between influenza viruses from wild migratory birds in Eurasia, has contributed to the increased diversity of the viral gene pool in eastern Asia; this has the potential to change the host range and to allow the virus to evolve into forms with increased pathogenicity.