Genetics of Japanese H5N8 high pathogenicity avian influenza viruses isolated in winter 2020–2021 and their genetic relationship with avian influenza viruses in Siberia

Abstract

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.

Different Infectivity and Transmissibility of H5N8 and H5N1 High Pathogenicity Avian Influenza Viruses Isolated from Chickens in Japan in the 2021/2022 Season

“…One of the representative HPAI strains in the 2020/2021 season, A/duck/Chiba/C1T/2021(H5N8)(ChibaC1T), which has the same gene constellation of group 20A [ 12 ], Akita7C, Kagoshima6T, and Iwate7T were antigenically analyzed by the cross HI test ( Table 3 ). Antisera against ChibaC1T crossly reacted with Akita7C and Iwate7T antigens, but the antibody titer against Kagoshima6T was 16-fold lower than that against ChibaC1T.…”

“…According to a previous study [ 25 ], humoral immunity against avian influenza virus strains with similar antigenicity modulates reinfection in mallard ducks. Our analysis revealed that antisera against ChibaC1T(H5N8), which caused outbreaks in Japan in the 2020/2021 season and contains a gene constellation matching that of 20A [ 8 , 12 ], cross-reacted with the Akita7C antigen but not with Kagoshima6T ( Table 3 ). Thus, antibody responses against ChibaC1T in migratory birds may have reduced the prevalence of group 20A viruses in the 2021/2022 season.…”

“…Antigenic characteristics of HPAI strains were analyzed using the HI test described in the WHO manual on animal influenza diagnosis and surveillance using antiserum against HPAIVs [ 22 ]. Antisera against A/duck/Chiba/C1T/2021(H5N8) (ChibaC1T) [ 12 ], Akita7C, Kagoshima6T, and Iwate7T, were produced by immunizing chickens four times with 1.0 mg of the respective inactivated antigens (approved number 22-030 (7 July 2022)).…”

“…HPAIV infection was also confirmed in wild mammals (an Ezo red fox and a raccoon dog) in Hokkaido prefecture [ 9 , 11 ]. The number of poultry outbreaks in the 2021/2022 season was the second largest reported in Japan, followed by 52 outbreaks in the 2020/2021 season [ 12 , 13 ].…”

“…Sequencing analyses of HPAI strains isolated during the 2021/2022 season revealed that HPAIVs of H5N8 and H5N1 subtypes in clade 2.3.4.4B were introduced to poultry and wild birds in Japan, causing outbreaks of the season. Phylogenetic analyses based on the HA genes of all isolates from poultry revealed that the HA genes of Japanese H5N8 strains isolated in November 2021 were closely related to those of H5N8 strains of the E2 genotype isolated in Japan and Korea in 2020/2021 [ 8 , 12 , 14 ]. In contrast, the HA genes of Japanese H5N1 HPAIVs isolated in early and late periods of the 2021/2022 season (early 2021/2022: during November 2021–January 2022 and one case in May, late 2021/2022: during February 2022–May 2022) were closely related to those of H5N8 isolates in Europe in 2020/2021 and those of H5N1 isolates in Europe in 2021/2022, respectively [ 8 , 9 , 15 ] (a manuscript describing phylogenetic analyses of full genetic sequences of HPAIVs isolated in Japan during the 2021/2022 season is under preparation).…”