To elucidate the evolutionary pathway, we sequenced the entire genomes of 89 H5N6 highly pathogenic avian influenza viruses (HPAIVs) isolated in Japan during winter 2016-2017 and 117 AIV/HPAIVs isolated in Japan and Russia. Phylogenetic analysis showed that at least 5 distinct genotypes of H5N6 HPAIVs affected poultry and wild birds during that period. Japanese H5N6 isolates shared a common genetic ancestor in 6 of 8 genomic segments, and the PA and NS genes demonstrated 4 and 2 genetic origins, respectively. Six gene segments originated from a putative ancestral clade 2.3.4.4 H5N6 virus that was a possible genetic reassortant among Chinese clade 2.3.4.4 H5N6 HPAIVs. In addition, 2 NS clusters and a PA cluster in Japanese H5N6 HPAIVs originated from Chinese HPAIVs, whereas 3 distinct AIV-derived PA clusters were evident. These results suggest that migratory birds were important in the spread and genetic diversification of clade 2.3.4.4 H5 HPAIVs.
In our previous study, we genetically analyzed bovine viral diarrhea viruses (BVDVs)
isolated from 2000 to 2006 in Japan and reported that subgenotype 1b viruses were
predominant. In the present study, 766 BVDVs isolated from 2006 to 2014 in Hokkaido,
Japan, were genetically analyzed to understand recent epidemics. Phylogenetic analysis
based on nucleotide sequences of the 5′-untranslated region of viral genome revealed that
766 isolates were classified as genotype 1 (BVDV-1; 544 isolates) and genotype 2 (BVDV-2;
222). BVDV-1 isolates were further divided into BVDV-1a (93), 1b (371) and 1c (80)
subgenotypes, and all BVDV-2 isolates were grouped into BVDV-2a subgenotype (222). Further
comparative analysis was performed with BVDV-1a, 1b and 2a viruses isolated from 2001 to
2014. Phylogenetic analysis based on nucleotide sequences of the viral glycoprotein E2
gene, a major target of neutralizing antibodies, revealed that BVDV-1a, 1b and 2a isolates
were further classified into several clusters. Cross-neutralization tests showed that
BVDV-1b isolates were antigenically different from BVDV-1a isolates, and almost BVDV-1a,
1b and 2a isolates were antigenically similar among each subgenotype and each E2 cluster.
Taken together, BVDV-1b viruses are still predominant, and BVDV-2a viruses have increased
recently in Hokkaido, Japan. Field isolates of BVDV-1a, 1b and 2a show genetic diversity
on the E2 gene with antigenic conservation among each subgenotype during the last 14
years.
In winter 2020–2021, Japan experienced multiple serious outbreaks of H5N8 high pathogenicity avian influenza (HPAI)—52 outbreaks at poultry farms and 58 cases in wild birds or the environment—that occurred simultaneously with outbreaks in Europe. Here, we examined how the H5N8 HPAI viruses (HPAIVs) emerged and spread through Japan and across the Eurasian continent. Phylogenetic and phylogeographic analyses were performed using full genetic sequences of the viruses that caused 52 outbreaks at poultry farms or were isolated from 11 infected wild birds. Genetically, the viruses showed five genotypes (E1, E2, E3, E5 and E7) that have already been reported in Korea. The viruses showing the E3 genotype were found to have caused most of the HPAI outbreaks at poultry farms and were detected over the longest period of time. The internal genes of the viruses were genetically related to those of AIVs isolated through avian influenza surveillance activities in regions of Siberia including Buryatia, Yakutia and Amur regions, suggesting that the Japanese viruses emerged via reassortment events with AIVs genetically related to Siberian AIVs. In addition, H5N2 and H5N8 HPAIVs were isolated from wild birds during surveillance activities conducted in the Novosibirsk region of Siberia in summer 2020. Phylogenetic analyses revealed that these viruses possessed haemagglutinin genes that were related to those of H5N8 HPAIVs that were circulating in Europe in winter 2020–2021. These results suggest that the viruses in wild birds during summer in Siberia most likely spread in both Asia and Europe the following winter. Together, the present results emphasize the importance of continual monitoring of AIVs in Siberia for forecasting outbreaks not only in Asia but also further away in Europe.
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