Genetic analyses of avian influenza viruses in Mongolia, 2007 to 2009, and their relationships with Korean isolates from domestic poultry and wild birds.

The present study was conducted to monitor wild birds based on the concern that they could disseminate avian influenza virus (AIV) between Mongolia and Korea, which shares the same migratory flyway. Of 1,528 fecal samples analyzed, 21 low-pathogenic AIV were isolated from 2007 to 2009. Nineteen AIV-positive fecal samples were identified as Anseriformes by DNA bar coding. The most frequently isolated subtype was H3 (61.9%), and the most prevalent hemagglutinin/neuraminidase combination was H3N8 (52.4%). Phylogenetic analysis was performed to assess their genetic relationships with those of domestic poultry and wild birds in Korea. The H3 and H7 surface genes belonged to the Eurasian lineage and clustered together in a group with Korean wild birds and poultry. Most N8 genes clustered phylogenetically with viruses isolated in Eurasia, whereas 1 of the Mongolian viruses and some Korean viruses belonged to the North American lineage. The polymerase acidic protein of the internal gene was not distinguishable from the H5N1 highly pathogenic AIV of the goose/Guangdong/1/1996 (Gs/Gd)-like virus. Our study suggests that Mongolian AIV isolates have evolved with genetically multiple genotypes and are closely related to those of AIV in poultry as well as in wild birds in Korea.

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.

Surveillance of avian influenza virus in wild bird fecal samples from South Korea, 2003-2008.

We analyzed the results from nationwide surveillance of avian influenza (AI) from birds in South Korea's major wild bird habitats and the demilitarized zone of South Korea, 2003-2008. Of 28,214 fecal samples analyzed, 225 yielded influenza viruses, for a prevalence of 0.8%. Hemagglutinin (HA) subtypes H1-H12 and all nine neuraminidase (NA) subtypes were detected. The dominant HA subtypes were H6, H1, and H4, and the most common NA subtypes were N2, N1, and N6. Among the 38 HA/NA subtype combinations, the most common were H4N6, H6N1, and H5N2. Thirty-seven low-pathogenic AI (LPAI) viruses of the H5 and H7 subtype were detected. Among them, we identified bird species for 16 H5- and H7-positive fecal samples using a DNA bar-coding system instituted in 2007; all birds were identified as Anseriformes. The HA gene of the H5 wild bird isolates belonged to the Eurasian avian lineage, and could be clearly distinguished from the sublineage H5N1 highly pathogenic AI (HPAI) of the Eurasian and American avian lineages. Whereas H7 LPAI viruses did not group as a separate sublineage with H7 HPAI viruses, H7 isolates were closely related with the Eurasian avian lineage.

Survival rate of H5N1 highly pathogenic avian influenza viruses at different temperatures.

The survival rate of Korean H5N1 highly pathogenic avian influenza (HPAI) viruses was investigated at different temperatures under the laboratory conditions. The estimated survival days for a starting viral concentration of 10(6.5) 50% egg infectious dose/0.1 mL were 930, 1,042, and 3,213 d at 4 degrees C; 226, 232, and 293 d at 20 degrees C; and 51, 55, and 58 d at 30 degrees C for A/chicken/Korea/ES/03, A/chicken/Korea/IS/06, and A/chicken/Korea/Gimje/08 (Gimje/08) viruses, respectively. The stability of the Gimje/08 virus was statistically significant compared with the other 2 viruses except for the data between Gimje/08 and A/chicken/Korea/IS/06 virus at 30 degrees C. This result indicated that the survival rate of 3 Korean HPAI viruses is different at various temperatures, which might have partially influenced the large scale of HPAI outbreak in Korea in 2008.