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.