Understanding the transmission of African swine fever in wild boars of South Korea: A simulation study for parameter estimation

Abstract

Since the introduction of African swine fever (ASF) to Georgia in 2007, the disease has spread to many other countries including South Korea. Initial detection of ASF from wild boars (WB) in South Korea was reported in early October 2019. Since then, more than a thousand WB samples collected from the northern part of the country have been confirmed as ASF positive (2.9% of ASF positivity among WB samples collected until June 2020), indicating that the disease is endemic in the WB populations. To control the disease, multiple layers of fence‐lines have been erected. Nevertheless, outbreaks continuously occurred across the fence, requiring a better understanding of the spatial transmission mechanism of ASF in WBs. Hence, we developed a novel ASF transmission model to estimate ecological and epidemiological parameters related to the spread of the disease in the WB population of South Korea. The results showed that roads and rivers were effective to prevent the spread, reducing the transmission rate to approximately 37% on average. Only a limited level of reduction was indicated via fence‐lines, implying erection of fences might be considered as a temporary measure to delay the spread. This study also revealed that the probability of ASF transmission to adjacent habitats considerably decreased with increasing distance, supporting the slow spatial transmission speed reported from other European countries. Considering that elucidation of ASF dynamics in WB is crucial to mitigate the impact of the disease, we believe this study provides some useful ecological and epidemiological implications to control the disease in future.

Three Years of African Swine Fever in South Korea (2019–2021): A Scoping Review of Epidemiological Understanding

“…Although the indirect transmission by ASF-positive wild boar carcasses has been regarded as comparable to the direct transmission by ASF-positive live wild boar in various contexts [42], the contribution of indirect transmission in South Korea is yet to be quantifed. A simulation study, which incorporated the ecological features of the wild boar population in South Korea, quantifed the transmission rate (β) for direct contact in wild boar at 0.016/week, consistent with previous studies [38]. However, the estimated β due to indirect contacts with ASFpositive wild boar carcasses could not be diferentiated from the estimated β due to direct contacts, which might be because the model did not incorporate the infection pressure from environments contaminated by an ASF-positive carcass or was too complex in comparison to the data [38].…”

“…In South Korea, where ASFV in wild boar has invaded from the north to the south, the characteristics of the invasion show some similarities with the EU context, but have diferent implications. Te short-distance dispersal by wild boar was slow in South Korea, which is consistent with the EU context; the infection pressure on wild boar in neighbouring habitats was lowered to approximately 15%, compared to the infection pressure on individuals in the same geographical habitat, which was likely due to the fact that wild boar rarely interact with other boars in diferent habitats in South Korea [38]. Te invasion was predicted to occur predominantly through forests and mountains, which raised the concern that ASFV would be disseminated throughout the country, 70% of which is covered by forests and mountains.…”

“…While the efects of fences on preventing the disease from spreading in wildlife are questionable [51], they were shown to slow the spread in South Korea. Te third fencing (national fencing) was found to decrease the infection pressure on individuals in the neighbourhood habitat by 47% compared to the infection pressure on individuals in the same geographical habitat [38]. Te authors suggest that it might be used as a temporary measure to buy time.…”

“…Te authors suggest that it might be used as a temporary measure to buy time. Environmental and anthropogenic fragmentations such as rivers and highways were shown to have a higher efect, decreasing the infection pressure by 65% [38].…”

“…Successfully unravelling the underlying disease dynamics in wild boar would make it possible to quantify the spatial range of wild boar-mediated transmission, determine the true area of ASF-afected regions, and potentially guide the optimal place and time to implement fencing and depopulation. Despite its implications on wild boar ASF epidemiology, only three studies out of ten for wild boar adjusted or took into account the performance of the surveillance system to understand disease distribution or disease dynamics [32,36,38].…”