R06.1 Examining the Impact of Fencing on the Front Wave of African Swine Fever in the Korean Wild Boar Population

Abstract

African Swine Fever (ASF) is a viral disease that affects both wild boar and domestic pigs. In recent years, this virus has spread rapidly across Europe and Asia, causing extensive damage to pig populations and related industries. In South Korea, the first notification in wild boar was made in October 2019 in the northern region bordering North Korea. Since then, the virus spread southward, leading to more than 2,800 reported cases in wild boar and sporadic outbreaks in domestic pig farms. To mitigate its spatial spread, Korean authorities built fences over 2,300 km. In this study, we aimed at evaluating the effectiveness and its heterogeneity of these fences in controlling the spread of ASF in South Korea, using the spatiotemporal distribution of ASF cases reported in wild boar between November 2019 – March 2023 in South Korea.

 We first identified the main spatiotemporal clusters and selected only the front wave cases within each cluster. By examining these front wave cases, we estimated the spread rate (in km²/week) using trend surface analysis (Tisseuil et al., 2016). Finally, to evaluate the effectiveness of fencing on the spread of ASF, we created a null scenario by randomly redistributing front wave case locations as described in Dellicour et al. (2020). By comparing the observed patterns to the expected patterns from the null scenario, we were able to test whether fences effectively reduced the spatial propagation of the virus as well as the front wave velocity.

Among the total 2,661 wild boar cases reported in the study period, we identified nine clusters that included 691 front wave cases. We restricted our analysis to the 619 front wave cases from the four largest clusters. Overall, the front wave spread by 0.52km² per week at national level, with heterogeneous velocities calculated in each cluster, from 0.15 km²/week to 0.99 km²/week. For two out of the four clusters studied, we found that the number of fence-crossing events was statistically significantly lower than under the null scenario, suggesting that fences reduced the propagation of the virus across the fences in these regions. However, we did not find any evidence for the two other clusters. Also, we did not find any statistical evidence suggesting that fences slowed down the front wave velocity.

We conclude that ASF virus in South Korea spread geographically at a faster rate than in other environmental contexts like Belgium (Dellicour et al., 2020) and that this geographical spread must be associated to specific determinants that are yet to be elucidated. The heterogeneous effects of fences can be explained by their spatio-temporal erecting patterns and environmental determinants. We highlight the crucial need to account for unobserved ASF virus diffusion when deciding where and when to place them.