Epidemiology and pathobiology of H5Nx highly pathogenic avian influenza in South Korea (2003-2024): a comprehensive review

Abstract

Since their emergence in Guangdong, China, in 1996, Gs/GD H5 highly pathogenic avian influenza viruses (HPAIVs) have diversified into multiple clades, spreading globally through wild bird migrations and causing substantial losses in poultry and wildlife. In South Korea, HPAIVs, including H5N1, H5N8, and H5N6 subtypes, have been repeatedly introduced since 2003. This review examines the epidemiology, genetic characteristics, and pathobiological features of these viruses in South Korea. Outbreaks typically occur between October and December, aligning with the arrival of wintering migratory birds. While outbreaks in poultry farms dominated before 2018, wild bird cases became more prevalent in subsequent years. Seasonal outbreaks in poultry have declined, but large-scale mortality events in wild birds emerged biennially from 2020. Genotypic diversity has increased since 2014 due to reassortment with low pathogenic viruses, with novel genomic traits detected in recent seasons. Infection studies show consistently fatal outcomes in chickens, while high mortality in domestic ducks was observed only with two of the studied strains, despite efficient transmission. Wild bird studies reveal species-specific roles in viral shedding and transmission. This review underscores the dynamic nature of HPAI outbreaks, highlighting the importance of surveillance, biosecurity, and genetic and pathogenicity analyses to mitigate future risks.

Keywords: Highly pathogenicity avian influenza; characteristics; outbreak; poultry; republic of Korea; wild bird.

Figure 1.

Timeline, case counts, and genotypes of highly pathogenic avian influenza (HPAI) outbreaks in South Korea from 2003 to 2023. The first three columns show duration and case counts of all HPAI H5 reports in South Korea, sourced from KAHIS (home.kahis.go.kr) and WADIS (wadis.go.kr), provided by the animal and plant quarantine agency and the wildlife disease control center, respectively. The leftmost column indicates the outbreak duration; ‘d’ stands for days. Outbreak periods are highlighted in red, marking the time between the first and last cases in each outbreak. Outbreaks are segmented if there is a gap of over four months (120 days) since the previous case, with the 2016–2017 period further divided by subtype. Case counts are represented by pink bars (poultry cases) and blue bars (wild bird cases). The two right columns display confirmed genotypes and reference studies corresponding to each outbreak period. Genotype names are presented as designated in each original reference. Bars inside black circles represent the eight gene segments of the virus, ordered from top to bottom as follows: polymerase basic 2, polymerase basic 1, polymerase acidic, hemagglutinin, nucleoprotein, neuraminidase, matrix, and nonstructural. Different bar colors indicate viral origins inferred from maximum-likelihood phylogenetic trees, according to the references in the fourth column. Black arrows indicate the direction of genetic contribution from donor viruses to newly emerged recombinant viruses. Asterisks indicate entries with different references, placed before the reference and after the genotype name.