Genetically Diverse Highly Pathogenic Avian Influenza A(H5N1/H5N8) Viruses among Wild Waterfowl and Domestic Poultry, Japan, 2021

Abstract

H ighly pathogenic avian influenza (HPAI) viruses are known to have zoonotic potential (1). There-

Detection of New H5N1 High Pathogenicity Avian Influenza Viruses in Winter 2021–2022 in the Far East, Which Are Genetically Close to Those in Europe

“…In winter 2021–2022, many H5N1 HPAIVs were introduced to the Far East, including Japan, Russia (Sakhalin), and the Republic of Korea [ 11 , 13 ]. Phylogenetic analysis results indicated that three groups of H5 HPAIVs were introduced into Japan, probably by bird migration.…”

“…Most H5N1 isolates in northern Japan in Group 1 were genetically close in all eight gene segments to those circulating in Europe and North America in the same season, indicating that these viruses did not cause any genetic reassortment events with local viruses and had the potential to travel for a longer distance, such as from nested lakes in the north to the Far East along the Sea of Okhotsk as well as European countries [ 13 ], and were simultaneously introduced into the Far East, Europe, and North America [ 9 , 25 ]. In parallel, H5 HPAIVs isolated in southern Japan and the Republic of Korea at the end of 2021 were genetically distinct from Group 1 [ 13 ] and formed two different genetic subgroups in the phylogenetic tree of the HA gene (Group 2 and 3). Viruses in Group 3 were genetically close to Asian isolates in 2020–2021 [ 11 , 12 , 13 ], implying that H5 HPAIVs, mainly the H5H8 subtype in Group 3, had been kept in the Far East since the winter of 2020–2021.…”

“…In parallel, H5 HPAIVs isolated in southern Japan and the Republic of Korea at the end of 2021 were genetically distinct from Group 1 [ 13 ] and formed two different genetic subgroups in the phylogenetic tree of the HA gene (Group 2 and 3). Viruses in Group 3 were genetically close to Asian isolates in 2020–2021 [ 11 , 12 , 13 ], implying that H5 HPAIVs, mainly the H5H8 subtype in Group 3, had been kept in the Far East since the winter of 2020–2021. Viruses in Group 2 were genetically close to European isolates in summer or autumn 2021 but distinct from the viruses in Group 1.…”

“…Phylogenetic analyses have already revealed that two types of H5 HPAIVs invaded southern Japan at the end of 2021. H5N1 HPAIV with slight mutations on the HA gene from the parental H5N8 HPAIV and H5N8 HPAIVs, similar to European dominant strains in winter 2020–2021, have been confirmed, whereas no H5N1 HPAIVs dominant in Europe in the same season have been detected [ 13 ].…”

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

“…The largest number of HPAI outbreaks was reported in Europe until 2022, with H5N1 the most dominant subtype in most countries. In the 2021/2022 season (i.e., from November 2021 to May 2022) in Japan, 25 HPAI outbreaks across 12 prefectures were reported in poultry farms (chickens, ducks, and emus), and 107 cases across 8 prefectures were confirmed in wild birds (e.g., a hooded crane [ 8 ], crows, and eagles [ 9 ]) or the environment [ 10 ]. HPAIV infection was also confirmed in wild mammals (an Ezo red fox and a raccoon dog) in Hokkaido prefecture [ 9 , 11 ].…”