The first African swine fever (ASF) virus infection in wild boar was reported in October in 2019 in Yeoncheon-gun. ASF control measures including passive/active surveillance, fencing, or hunting have been applied by the Korean government from the beginning of disease outbreak. Despite significant financial investment in ASF control strategies, the virus has continued to circulate among wild boars up to 2024. A basic reproduction number (R0) can be used to evaluate the effectiveness of ASF control strategy by providing the disease spread speed. During the ASF epidemic period, the spread speed could be estimated with the average number of new cases generated by an infected case. The current study estimated R0 for the 2019/24 ASF epidemics in wild boars in the Republic of Korea by using the daily reported number of ASF cases and the serial interval of ASF virus. The estimated mean R0 was 2.19 (range: 0.03 - 65.00) for the 2019/24 ASF epidemics, 3.05 (range: 0.70 - 10.40) in 2019, 2.01 (range: 0.06 - 9.79) in 2020, 1.94 (range: 0.07 - 7.35) in 2021, 4.71 (range: 0.21 - 61.95) in 2022, 1.93 (range: 0.11 - 7.53) in 2023, and 3.08 (range: 0.09 - 24.59) in 2024, respectively. Despite the ASF control measures, the ASF epidemic situation in wild boars was exacerbated. Targeted wild boar population management and active carcass searches are necessary to reduce the spread of ASF.

Since the first detection of African swine fever (ASF)-infected wild boar in October 2019, the ASF virus has been circulating among wild boars in the Republic of Korea. The priority for ASF control is to understand the epidemic situation correctly. The basic reproduction number (R0) can be used to describe the contagious disease epidemic situation since it can assess the contagiousness of infectious agents by presenting the average number of new cases generated by an infected case. The current study estimated R0 for the 2019/20 ASF epidemics in wild boars in the Republic of Korea using the reported number of ASF cases and a serial interval of the ASF virus. The estimated mean R0 was 2.10 (range: 0.06 – 10.24) for the 2019/20 ASF epidemics, 2.94 (range: 0.43 – 9.89) for the 2019 ASF epidemics, and 2.00 (range: 0.06 – 11.10) for the 2020 ASF epidemics. In addition, the estimated mean R0 was 3.82 (range: 1.16 – 8.78) in winter, 1.39 (range: 0.16 – 6.30) in spring, 4.82 (range: 0.26 – 17.08) in summer, and 2.21 (range: 0.51 – 5.86) in fall. Even though the Korean government has applied ASF control measures, including hunting or fencing, the ASF epidemic situation in wild boars has intensified. For ASF control in wild boars, tailor-made hunting, wild boar management, or active searching for carcasses are required to reduce the ASF virus. For ASF prevention in domestic pigs, no contact between wild boars and domestic pigs and a biosecurity plan by veterinarians are needed to decrease the risk of ASF virus transmission from wild boars to domestic pigs.