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. 2020 Feb 13;9(2):119.
doi: 10.3390/pathogens9020119.

Dynamics of Classical Swine Fever Spread in Wild Boar in 2018-2019, Japan

Norikazu Isoda  1   2 , Kairi Baba  3 , Satoshi Ito  1 , Mitsugi Ito  4 , Yoshihiro Sakoda  2   5 , Kohei Makita  3
Affiliations

Dynamics of Classical Swine Fever Spread in Wild Boar in 2018-2019, Japan

Norikazu Isoda et al. Pathogens. .

Abstract

The prolongation of the classic swine fever (CSF) outbreak in Japan in 2018 was highly associated with the persistence and widespread of the CSF virus (CSFV) in the wild boar population. To investigate the dynamics of the CSF outbreak in wild boar, spatiotemporal analyses were performed. The positive rate of CSFV in wild boar fluctuated dramatically from March to June 2019, but finally stabilized at approximately 10%. The Euclidean distance from the initial CSF notified farm to the farthest infected wild boar of the day constantly increased over time since the initial outbreak except in the cases reported from Gunma and Saitama prefectures. The two-month-period prevalence, estimated using integrated nested Laplace approximation, reached >80% in half of the infected areas in March-April 2019. The area affected continued to expand despite the period prevalence decreasing up to October 2019. A large difference in the shapes of standard deviational ellipses and in the location of their centroids when including or excluding cases in Gunma and Saitama prefectures indicates that infections there were unlikely to have been caused simply by wild boar activities, and anthropogenic factors were likely involved. The emergence of concurrent space-time clusters in these areas after July 2019 indicated that CSF outbreaks were scattered by this point in time. The results of this epidemiological analysis help explain the dynamics of the spread of CSF and will aid in the implementation of control measures, including bait vaccination.

Keywords: Japan; classical swine fever; space–time analysis; wild boar.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Positive rates of classical swine fever virus (CSFV) in wild boar. Results for CSFV antigen detection in wild boar in 12 prefectures were combined. Solid line: CSFV-positive rates in total animals tested in each week. Dashed line: CSFV-positive rates in animals captured in each week. Bar chart: The number of dead and captured wild boars tested in each week.
Figure 2
Figure 2
Distances of CSF cases in wild boar from the initial case over time.
Figure 3
Figure 3
Spatial change of two-month-period prevalence of CSF in wild boar.
Figure 4
Figure 4
Spatiotemporal distribution of classical swine fever notifications from April to November 2019.
Figure 5
Figure 5
Locations of the significant space–time clusters of CSF.
See this image and copyright information in PMC

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