Epidemiological studies of avian influenza

Recent outbreaks of highly pathogenic avian influenza (HPAI) have spread from southeast Asia to 62 Eurasian and African countries. H5N1 viruses isolated from dead water birds in Mongolia on the way back to their nesting areas in Siberia in April to May in 2005, 2006, 2008 and 2009 were genetically closely related to those isolated from birds in China, and some southeast Asian countries. It is now a serious concern that these HPAI viruses may perpetuate in the lakes where migratory water birds nest in summer.Therefore, virological surveillance of avian influenza virus in the migratory birds that fly from their nesting lakes in Siberia to Hokkaido, Japan was carried out in autumn every year. During 2008-2009, 62 influenza viruses of 21 different combinations of hemagglutinin (HA) and neuraminidase (NA) subtypes were isolated. Up to September 2010, no HPAI virus has been found, indicating that H5N1 HPAI virus has not perpetuated at least dominantly in the lakes where ducks nest in summer in Siberia. It is reported that the PB2 protein is a component of the viral polymerase complex that plays an important role in virus replication, and is a determinant of host range and pathogenicity of influenza viruses. The PB2 genes of 57 influenza viruses out of 283 influenza viruses isolated in Hokkaido in 2000-2009 were phylogenetically analysed. None of the genes showed close relation to those of H5N1 HPAI viruses that were detected in wild birds found dead in Eurasia on the way back to their northern territory in spring.Avian influenza virus strains isolated from migratory ducks in the global surveillance have been stored for the use for vaccines and diagnosis. Vaccine is used to reduce virus shedding into the environment and as an optional measure in cases where the disease spreads widely, in addition to stamping out. In the present study, the efficacy of the vaccine was comparable to that prepared from genetically modified HPAI virus strain ΔRRRRK rg-A/whooper swan/Mongolia/3/2005 (H5N1), which is more antigenically related to the challenge virus strain, in chickens. Inactivated influenza virus vaccine prepared from a non-pathogenic influenza virus strain A/duck/Hokkaido/Vac-1/2004 (H5N1) from the virus library conferred protective immunity to chickens against the challenge of antigenically drifted HPAI virus, A/whooper swan/Hokkaido/1/2008 (H5N1).