DISCUSSION
The probability of ASF introduction into South Korea via legal imports of live pigs and pig products was found to be negligible. The number of countries eligible to export live pigs and pig products to South Korea is currently 11 and 22 countries, respectively (Regions with an import ban on designated quarantine products, Notification of MAFRA No. 2019-37, Enforcement on 30 July 2019). All import health requirements (IHRs) for both items imported to South Korea stipulate that the importing countries should be ASF-free for at least 3 years prior to shipping. Of the assessed countries which exported live pigs and pig products to South Korea, only two countries have suffered from ASF outbreaks. In Italy ASF is restricted only to Sardinia and South Korea imports pig products from the unaffected regions of the country. In Poland with the highest probability via legal import of pig products ASF has been present since 2014. However, an import ban on pig products from Poland has been imposed immediately after the first ASF outbreak notification in wild boars in February 2014. Countries with ASF outbreaks are only allowed to import sterilized pig products to South Korea (Regions with an import ban on designated quarantine products, Notification of MAFRA No. 2019-37, Enforcement on 30 July 2019; Range and criteria for sterilization, pasteurization and process of designated quarantine products, Notification No. 2018-24 of APQA, Enforcement on 13 Sep 2018). This policy may also play an important role in blocking the ASF risk of introduction through the legal imports of pig products.
The probabilities of release through the analyzed pathways were very low, but the possibility of exposure to the pig population cannot be ignored. In South Korea, swill feeding after heat treatment at 80 °C for 30 min is permitted. This heat treatment is below the recommendation of the OIE (90 °C for 60 min) and, therefore, is more than likely not sufficient to inactivate ASFV in the food scraps used for feed. In addition, a high density of wild boars inhabits the country. Thus, ASFV can be exposed to wild boar populations if they are able to access landfills or other areas used for food disposal. To mitigate this probability of exposure, heating food scraps at higher temperatures and for longer time periods to feed pigs should be reinforced for a short term. The proportion of food waste used for swill feeding and landfills should be decreased and replaced with the production of biogas in the long term.
Totally 14 ASF cases occurred during September-October 2019 in the domestic pig farms of northern region of South Korea around the border with North Korea. Pre-emptive slaughter and culling of domestic pig farms in the infected region were conducted, while 485 cases have been confirmed in wild boar population there from 2 October 2019 to 6 April 2020. The control of infected wild boars to block the further transmissions to domestic pig population is of major concerns in the country now. In spite of ongoing investigations, source of infection is not specified yet. However, there is possibility of ASF introduction via other routes like illegal import of live pigs or pig products, import of feed, introduction of food waste from international airplanes/ships and their use for swill feeding, and potential contaminated materials carried by foreign workers, vehicles or other fomites. These pathways need to be assessed and subsequent preventive measures should be followed for the efficient concentration of limited quarantine personnel and financial resources.