From Clustered to Sporadic: Structural Shifts in the Spatiotemporal Dynamics of HPAI Following the 2017 Policy Reinforcement in South Korea (2003–2025)
TL;DR
It is suggested that the post‐2017 pattern was temporally consistent with strengthened control policies aimed at reducing mechanical connectivity between farms, although this ecological analysis cannot separate policy effects from other time‐varying epidemiological and surveillance‐related factors.
Abstract
Highly pathogenic avian influenza (HPAI) is a devastating viral disease causing substantial economic losses in the poultry industry and posing potential zoonotic risks. Located along the East Asian–Australasian Flyway (EAAF), South Korea has experienced recurrent outbreaks of HPAI since 2003. Following the severe 2016–2017 epidemic, the government implemented strengthened control measures, including restrictions on duck farming and organizational restructuring. This study quantitatively evaluated structural changes in the spatiotemporal patterns and transmission dynamics of HPAI before and after the 2017 policy reinforcement, utilizing a complete dataset covering 12 epidemic waves between 2003 and 2025. Our analysis suggests a distinct shift in HPAI occurrence patterns from large‐scale, clustered epidemics to more sporadic occurrences in the post‐2017 period. Pre‐2017 epidemics, particularly the 5th and 6th waves, exhibited intense spatiotemporal clustering and high transmission potential. Conversely, post‐2017 epidemics showed a significant reduction in outbreak density and the disappearance of large‐scale clusters. Notably, the 12th wave displayed a more circular diffusion pattern with outbreaks confined to specific regions, suggesting relatively more geographically contained spread. However, despite the overall reduction in scale, high spatiotemporal interaction intensity was intermittently observed, such as in the 11th wave, indicating that residual risks of explosive local transmission persist even during smaller epidemics. These findings suggest that the post‐2017 pattern was temporally consistent with strengthened control policies aimed at reducing mechanical connectivity between farms, although this ecological analysis cannot separate policy effects from other time‐varying epidemiological and surveillance‐related factors. Nevertheless, a decline in case numbers does not necessarily imply the elimination of local transmission risk, highlighting the need to advance precise and risk‐based surveillance and response strategies to effectively manage residual risks.