National Institute of Animal Health, NARO

Source of classical swine fever infection in wild boars in Yamaguchi Prefecture is possibly about 500 km away

-Countermeasures against long-distance transmission is required as the classical swine fever can spread not only to nearby wild boars-

National Agriculture and Food Research Organization (NARO) has performed genetic analysis of the classical swine fever virus (CSFV) obtained from the wild boar in Yamaguchi Prefecture, which was confirmed positive in March 2022. It was revealed that it is most closely related to the virus obtained from the wild boar in the eastern part of the Kii Peninsula, about 500 km away from Yamaguchi Prefecture, whose infection was confirmed in May 2021. This result indicates the need for countermeasures against long-distance transmission of the virus.


Overview

In March 2022, a wild boar infected with classical swine fever (CSF) was confirmed in Yamaguchi Prefecture. Since no positive cases of wild boar have been confirmed in the area nearby the detected wild boar at that time, the source of virus infection has grabbed attention. The gene of the virus obtained from the infected wild boar in Yamaguchi Prefecture was compared with the virus obtained from the wild boar which was found to be infected in Japan in the past. As a result, it was revealed that this virus differs from the virus obtained from infected wild boars found in places relatively close to Yamaguchi prefecture such as Hyogo prefecture. At the same time, it was found to be most closely related to the virus obtained from the infected wild boar found in the eastern part of the Kii Peninsula, about 500 km away in May 2021.

In September 2018, the outbreak of CSF was confirmed in a pig farm in Gifu prefecture for the first time in 26 years. Then it was confirmed in wild boars also. With the expansion of wild boar-infected areas, outbreaks continued at pig farms near the site where wild boar infection was confirmed. It is thought that transmission between wild boars are mainly caused by infection of wild boars around the infected wild boar and it is known that it rarely spreads to relatively remote areas. This time, the genetic information of the virus indicates that such long-distance transmission may have actually occurred. Since it is unlikely that such long-distance transmission will occur solely due to infection by wild boar movement or contact between wild boars, etc. there is concern that the CSFV may have been brought to remote areas through some human activity.


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