Introduction
African swine fever (ASF) is a highly contagious disease occurring in domestic pigs and wild suids, and leads to serious haemorrhage and nearly 100% mortality. ASF is caused by infection with African swine fever virus (ASFV; family: Asfarviridae , genus: Asfivirus ) (Dixon et al., 2020). Since its original description in the 1920s in Kenya, this viral disease has been highly prevalent in African and European countries. In Asia, ASF was first reported in a farm neat Shenyang City in Liaoning province in China, in August 2018 (Zhou at al., 2018). Thereafter, it quickly spread to other countries in Southeast Asia including Myanmar, Laos, Vietnam, and the Philippines, as well as nearly all provinces in mainland China, in 2019 (Lu et al., 2020). ASF outbreaks have also been described in North and South Koreas in the same year (Kim H. J. et al., 2020; Kim S. H. et al., 2020).
Despite the high mortality rates and socio-economic impacts of ASF, no vaccines or therapeutic agents are available for controlling its outbreak or its effective treatment (Dixon et al., 2020). Therefore, studies on the routes and patterns of ASF transmission as well as its early detection are urgently needed. Molecular epidemiology approaches using polymorphic DNA sequences can provide insight into the spatiotemporal patterns of disease transmission throughout the areas in which ASF is prevalent. The genomic DNA of ASFV shows a low evolution rate. Nevertheless, multiple sites show inter-genomic polymorphisms, particularly those containing short tandem repeats (STRs), which can be selected as informative markers in epidemiological investigations (Goller et al, 2015; Nix et al, 2006).
After ASFV was first isolated from a wild boar in October 2, 2019 in South Korea (Kim S. H. et al., 2020), we conducted a surveillance programme for wild boars in the relevant areas by the National Institute of Environmental Research (NIER). Genotypes of ASFV DNAs obtained during these surveys were investigated via polymerase chain reaction (PCR) and nucleotide sequencing to trace viral transmission in the wild boar population and monitor the probable emergence of viral variants.