Spatiotemporal Dynamics of Highly Pathogenic Avian Influenza H5 Virus Introductions and Regional Spread in the Republic of Korea

Abstract

Highly pathogenic avian influenza (HPAI) viruses from clade 2.3.4.4 have caused recurrent outbreaks in poultry since 2014. In the Republic of Korea, clade 2.3.4.4b viruses have driven five epidemic waves, yet the factors underlying HPAI introduction and farm-to-farm spread remain poorly understood. We compiled hemagglutinin gene sequences of clade 2.3.4.4b viruses from wild birds and poultry in the Republic of Korea (October 2016-March 2024) and reconstructed dispersal dynamics using Bayesian phylogeography. Dispersal patterns suggest that domestic duck farms in the western provinces likely form a key interface for spillover from wild birds into poultry. Mixed-effects generalized linear models showed that both wild-to-poultry and farm-to-farm transition rates were positively associated with the number of poultry farms in the destination province, while wild-to-poultry rates were further associated with higher avian influenza virus infection probability among wild birds. Wild-to-poultry transition rates were lower in 2020-2024 than in 2016-2018, which may reflect strengthened interventions. These findings suggest that poultry farm abundance and introduction pressure from wild birds jointly shape the spatial dynamics of HPAI introduction and spread. More broadly, these factors may provide operational indicators to guide risk-based surveillance and control strategies. Author SummaryHighly pathogenic avian influenza (HPAI) H5 viruses continue to cause major losses in poultry and pose recurring risks at the wildlife-livestock interface. Effective control depends on identifying where viruses are most likely to enter poultry populations and how they spread between farms. Using viral genomic data from wild birds and poultry in the Republic of Korea, this study suggests that domestic duck farms in western provinces likely form a key interface for introductions from wild birds into poultry. We also found that regions with more poultry farms were more likely to receive and spread the virus, while introduction risk was further elevated where infection pressure from wild birds was higher. By linking viral genomic patterns with ecological and epidemiological information, our study helps identify where HPAI viruses are most likely to enter poultry populations and spread between farms. These findings can guide targeted surveillance and early control in regions at greatest risk.