Evolution and Spread of Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus in Wild Birds, South Korea, 2022–2023

Abstract

During October 2022–March 2023, highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b virus caused outbreaks in South Korea, including 174 cases in wild birds. To understand the origin and role of wild birds in the evolution and spread of HPAI viruses, we sequenced 113 HPAI isolates from wild birds and performed phylogenetic analysis. We identified 16 different genotypes, indicating extensive genetic reassortment with viruses in wild birds. Phylodynamic analysis showed that the viruses were most likely introduced to the southern Gyeonggi-do/northern Chungcheongnam-do area through whooper swans ( Cygnus cygnus ) and spread southward. Cross-species transmission occurred between various wild bird species, including waterfowl and raptors, resulting in the persistence of HPAI in wild bird populations and further geographic spread as these birds migrated throughout South Korea. Enhanced genomic surveillance was an integral part of the HPAI outbreak response, aiding in timely understanding of the origin, evolution, and spread of the virus.

Surveillance and Genetic Analysis of Low-Pathogenicity Avian Influenza Viruses Isolated from Feces of Wild Birds in Mongolia, 2021 to 2023

“…South Korea has experienced continual outbreaks of HPAI since 2003, and since 2020, these outbreaks have caused significant socio-economic losses during four consecutive winter seasons (2020-2024) [13]. Previous studies suggested that the incursion of HPAI viruses into East Asia is predominantly attributed to viral strains originating from breeding grounds in Eurasia [15].…”

“…In Korea, HPAI viruses, especially H5Nx viruses from various clades of the Goose/ Guangdong lineage, have been seasonally detected in poultry since 2003 [13]. It has been suggested that viral reassortment occurs at breeding sites in Siberia, and that these newly generated variants are introduced into East Asia, including Korea, during the winter migration of wild birds [14].…”

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

“…The number of genotypes in Japan in 2022–2023 was the highest since the initial outbreak of the Gs/Gd virus in 2004 ( Mase et al, 2005 ), and higher than the five genotypes identified in 2020–2021 and 2016–2017 ( Mine et al, 2022 , Takemae et al, 2017 ). Recently, multiple HPAIVs with different gene constellations have been isolated in Asian countries (e.g., China in 2021–2022 ( Yang et al, 2023 ) and Korea in 2022–2023 ( Kang et al, 2023 , Lee et al, 2023 , Seo et al, 2024 )). H5 HPAIVs of multiple genotypes (more than 60 genotypes since 2020 and 16 genotypes in 2022–2023) have also been detected in Europe ( European Food Safety Authority 2023a ).…”

Index case of H5N1 clade 2.3.4.4b highly pathogenic avian influenza virus in wild birds, South Korea, November 2023

“…In South Korea, the H5N1 2.3.4.4b HPAI virus caused multiple outbreaks in wild birds and poultry from October 2022 to its eradication in March 2023, with 75 cases in poultry farms and 174 cases in wild birds reported ( 8 ). Until this report, the H5N1 2.3.4.4b HPAI virus responsible for the outbreaks in South Korea had not been detected in birds since April 2023, despite large-scale active surveillance targeting both wild birds and poultry.…”