INTRODUCTION
African swine fever (ASF) was described by Montgomery in Kenya in 1921 for the first time. Since then, the disease has been considered endemic in most of the Sub-Saharan countries. The first period of ASF epidemics out of Africa started in 1957 in Portugal and lasted until 1999. However, the ASF epidemiological situation dramatically changed in 2007 when an ASF outbreak was unexpectedly reported in Georgia (Rowlands et al. , 2008). From there, ASF spread to the other Caucasian countries and to the southern part of the Russian Federation in one year (Gogin et al. , 2012). Despite surveillance and control measures in the Russian Federation, ASF continues to spread in the country with significant economic consequences that were estimated to be 0.8-1 billion USD until October 2009 (USDA, 2010). A report indicated that ASFV was isolated from wild boars in Iran in 2008 (Rahimi et al. , 2010). The virus also moved to northwestern countries like Ukraine and Belarus in 2012 and 2013, respectively. European Union member states such as Lithuania, Latvia, Estonia and Poland were affected by the movements of the infected wild boars in 2014. There were notifications regarding ASF outbreaks in Romania and in the Czech Republic in 2017. In August of 2018, ASF was introduced in China, a country with particularly close socio-economic ties with South Korea (OIE, 2019) and other countries like Mongolia, Vietnam, Cambodia, North Korea, and Laos which have just became infected. South Korea reported the first ASF case in 17 September 2019. Until 9 October 2019, 14 cases occurred in the Northern region of the country. In spite of comprehensive epidemiological investigations, the source of infection is not determined yet.
The movement of live animals and their products is an important route of entry and transmission of ASF. Considering this, the World Trade Organization (WTO) and the World Organization for Animal Health (OIE) encourage member countries to refer to the guidelines of the Sanitary and Phytosanitary Measures Agreement (SPS) and create relevant policies after conducting the necessary risk assessments. According to the guidelines of the SPS, live pigs and pig products from ASF infected zones or countries are not allowed to be traded with ASF-free nations or areas (OIE, 2018a). Once a region reports an ASF outbreak, an immediate ban of the movement of live pigs and their products is implemented. However, live pigs and pig products with ASFV can escape freely from the infected region and be imported to other ASF-free countries legally during the HRP (High Risk Period) (i.e., which means the time period from the first ASF case (index case) in one country/region to the detection and notification of the disease in that country/region, before international trade is banned), which is the period of time from the initial infection of the index farm to the official detection and notification of an ASF outbreak (Horst et al. , 1998). Only 1 or 2 weeks have been shown to be sufficient for the extensive spreading of FMD and CSF during the HRP through the movements of animals in some European countries in recent epidemics (Bouma et al. , 2003; Greiser-Wilke et al. , 2000).
Considering the historical transcontinental and transboudnary transmissions of ASF, there are several routes of ASF entry that need to be considered: legal or illegal import of live pigs or pig products or feed, introduction of food waste from international airplanes/ships and their use for swill feeding, movement of infected wild boars, other potential contaminated materials carried by foreign workers, vehicles or other fomites. Though the movement of infected wild boars is of major concerns in South Korea now, it is necessary to assess the probability of ASF introduction by each possible route in order to block its entry into the country effectively. This study aimed at assessing the probability of ASF introduction into South Korea through legal import of live pigs and pig products during the high risk period (HRP) using a quantitative stochastic approach during 2009-2018.