Model specifications for the live pigs imported legally
A quantitative stochastic risk assessment for ASF introduction into South Korea via live pigs imported legally was modelled using an approach similar to that described in previous studies (Herrera-Ibatáet al. , 2017; Mur et al. , 2012). Canada, Denmark, France, Japan, United Kingdom (UK), and United States of America (USA) exported live pigs to South Korea during the last decade. All these countries have not reported ASF outbreaks in domestic pigs during the study period (Table 1).
To estimate the probabilities, four major assumptions were used: 1) If there were no ASF notifications in the country of origin for the study period, the probability of ASF outbreak in the country was estimated 1 outbreak in 1,000 years as maximum; 2) In order to estimate the number of ASF outbreaks during the HRP, all of the origin countries were assumed to have the same level of surveillance and export animal product quarantine capacity; 3) All imported live pigs have destination to farms; 4) ASFV will be always present in an acute form considering the characteristic of the current ASFV in Eurasia.
Risk analysis for the introduction of infectious agents through imports consists of 3 steps: release, exposure and consequence assessment (OIE, 2010). In this study, the probability of release (Pre ) and exposure (Pex)to a susceptible pig population in South Korea was assessed. The final probability (Pf(trade of live pigs) ) reflects the probability that an ASFV infected pig from country of origin is imported to a country of destination, thus resulting in ASF transmission to local pig population. Pf(trade of live pigs) was modelled using a binomial process as suggested by the OIE Risk Analysis handbook (OIE, 2010) as follows:
\begin{equation} P_{f(trade\ of\ live\ pigs)}=\ \sum{1-{\left(1-P_{\text{re}}\times P_{\text{ex}}\right)\ }^{n_{\text{odm}}}}\nonumber \\ \end{equation}
In this formulation nodm is the number of imported live pigs from a country of origin o to a country of destination d during the month m .