Genetics of H5N1 and H5N8 High-Pathogenicity Avian Influenza Viruses Isolated in Japan in Winter 2021–2022

Abstract

In winter 2021–2022, H5N1 and H5N8 high-pathogenicity avian influenza (HPAI) viruses (HPAIVs) caused serious outbreaks in Japan: 25 outbreaks of HPAI at poultry farms and 107 cases in wild birds or in the environment. Phylogenetic analyses divided H5 HPAIVs isolated in Japan in the winter of 2021–2022 into three groups—G2a, G2b, and G2d—which were disseminated at different locations and times. Full-genome sequencing analyses of these HPAIVs revealed a strong relationship of multiple genes between Japan and Siberia, suggesting that they arose from reassortment events with avian influenza viruses (AIVs) in Siberia. The results emphasize the complex of dissemination and reassortment events with the movement of migratory birds, and the importance of continual monitoring of AIVs in Japan and Siberia for early alerts to the intrusion of HPAIVs.

Genetic diversity of H5N1 and H5N2 high pathogenicity avian influenza viruses isolated from poultry in Japan during the winter of 2022–2023

“…The G2b group was previously defined as being composed of H5N1 HPAIVs isolated in Japan during the early period of 2021–2022 ( Takadate et al, 2023 , Mine et al, 2024 ). From our phylogenetic analysis, HPAIVs that caused 17 outbreaks across five prefectures in 2022–2023 were also classified into the G2b group because they clustered with G2b viruses from 2021 to 2022, such as A/chicken/Hokkaido/21D3T/2022(H5N1) ( Fig.…”

“…The clade of the virus genes was classified based on the results of phylogenetic analyses (e.g., formation of clusters with fast-global bootstrap values ≥75 % and the co-clustered virus genes). G2b and G2d viruses from 2021 to 2022 ( Takadate et al, 2023 , Mine et al, 2024 ) were used to verify the G2b and G2d viruses from the winter of 2022–2023. A/goose/Hunan/SE284/2022(SE284) (H5N1) ( Cui et al, 2022 ) was used to categorize G2c viruses from the winter of 2022–2023.…”

“…In Japan, we have experienced several outbreaks due to clade 2.3.4.4b HPAIVs. HPAIVs since the winter of 2020–2021 were classified into G1 and G2 groups, which are descendants of HPAIVs circulating in Europe in early and late 2020, respectively ( Mine et al, 2022 , Takadate et al, 2023 , Mine et al, 2024 , Baek et al, 2021 ). In 2020–2021, H5N8 viruses in the G1 and G2 groups caused 52 outbreaks in poultry premises and 58 cases in wild birds ( Mine et al, 2022 ).…”

“…In 2021–2022, H5N8 and H5N1 viruses belonging to the G2 group caused 25 outbreaks in poultry premises and 107 wild bird cases ( Takadate et al, 2023 ). Phylogenetic analyses revealed that HPAIVs in 2021–2022 were further divided into G2a, G2b, and G2d groups ( Mine et al, 2024 ). The G2a group (previously defined as E2 and 20A) was responsible for outbreaks in Japan and Korea in 2020–2021, whereas the origins of G2b and G2d viruses (previously defined as 20E and 21E, respectively), which were first introduced into Japan in 2021–2022, were H5N8 HPAIVs in Europe in 2020–2021 and H5N1 HPAIVs in Europe in 2021–2022, respectively.…”

Novel Genotype of HA Clade 2.3.4.4b H5N8 Subtype High Pathogenicity Avian Influenza Virus Emerged at a Wintering Site of Migratory Birds in Japan, 2021/22 Winter

“…In this study, we surveyed environmental water and fecal samples for AIVs at a wintering site of migratory waterfowls in Tottori, Japan, during the winter and spring migration [18] of one season (December 2021 to March 2022) and isolated HPAIV A/water/Tottori/NK1201-2/2021 (H5N8) (NK1201) [19]. Recently, various genotypes of H5Nx clade 2.3.4.4b HPAIVs [19][20][21][22][23][24] and H7N7 LPAIVs [24] have been detected in Japan. H5N8 and H5N1 HPAIVs isolated in the 20221-2022 winter season in Japan were divided into three groups (G2a, G2b, and G2d) based on their HA gene sequences [19].…”