Results and Discussion
The annual probability of ASF entry into Japan in January 2020 was 23% (90% prediction interval: 0-91%), slightly increased compared to the average annual probability in 2019 mainly due to the increase of air travelers from China. However, it decreased dramatically during the following three months: 4.7% (0-24%) in February, 0.4% (0-2.1%) in March and 0.004% (0-0.01%) in April 2020, due to the decrease both in the number of travelers from China and the amount of food waste from restaurants (Fig. 1).
These results indicate that there has been a dramatic decline in the ASF entry risk into Japan in early 2020, a reduction of 5000 fold. Although the model used in this study did not consider the entry risk relating to foreign workers, this risk is also predicted to be lowered as there were fewer foreign workers coming to work on farms in Japan under the travel restrictions (Nikkei Business News, 2020).
The ASF entry risk should be periodically monitored so that, depending on the predicted risk, Japanese pig farmers can be on alert to protect their farms from the introduction of ASF. The authors recommend that they utilize this low risk time to raise their level of biosecurity by, for example, contracting a veterinarian to develop an animal health plan and making a structural change in relation to pig houses, their layout and security fencing. This also applies to pig farms in other countries and regions where the ASF’s entry risk was high until last year and declined in the COVID 19 pandemic.