Role of Wild Boar in the Spread of Classical Swine Fever in Japan

Abstract

Since September 2018, nearly 900 notifications of classical swine fever (CSF) have been reported in Gifu Prefecture (Japan) affecting domestic pig and wild boar by the end of August 2019. To determine the epidemiological characteristics of its spread, a spatio-temporal analysis was performed using actual field data on the current epidemic. The spatial study, based on standard deviational ellipses of official CSF notifications, showed that the disease likely spread to the northeast part of the prefecture. A maximum significant spatial association estimated between CSF notifications was 23 km by the multi-distance spatial cluster analysis. A space-time permutation analysis identified two significant clusters with an approximate radius of 12 and 20 km and 124 and 98 days of duration, respectively. When the area of the identified clusters was overlaid on a map of habitat quality, approximately 82% and 75% of CSF notifications, respectively, were found in areas with potential contact between pigs and wild boar. The obtained results provide information on the current CSF epidemic, which is mainly driven by wild boar cases with sporadic outbreaks on domestic pig farms. These findings will help implement control measures in Gifu Prefecture. 108 domestic pig (DP) (square) and wild boar (WB) (circle). Ellipses with centroids were combined to indicate the 109 directional trend of the CSF outbreaks.110 2.2. Multi-Distance Spatial Cluster Analysis 111The multi-distance spatial cluster analysis was applied to explore the maximum distance 112 between cases of CSF notifications. The results indicated that 23 km was the maximum distance of 113 the significant spatial association between CSF notifications in Gifu Prefecture. The obtained 114 maximum distance was used in the subsequent analyses. 115 2.3. Kernel Density Estimation Analysis 116The kernel density estimation analysis was applied to describe the spatial distribution of the CSF 117 notifications. The analysis showed that the highest density of CSF notifications was located in the 118 southern part of Gifu Prefecture (Figure 2) with further expansion to the east. Among the 16 CSF-domestic farms were located in areas with very low density of notifications (80%), followed by areas 122 with low density (20%). The analysis revealed that CSF-positive farms were located in areas with 123 higher density of notifications, whereas the non-affected farms tended to locate in areas with low 124 density. 125 126 Figure 2. Density of CSF notifications in Gifu Prefecture.127 The heat map illustrates the estimated kernel density of CSF notifications (notifications/km 2 ) from very high 128 (red) to very low (transparent). Each coloured area indicates the density of CSF notifications per square 129 kilometer: very high (> 0.400), high (0.300-0.399), medium (0.200-0.299), low (0.100-0.199), and very low (< 130 0.100). The highest density of CSF notifications was located in the southern part of Gifu Prefecture. A very low 131 density of CSF notifications was located in other areas of the pr...

Rapid Spread of Classical Swine Fever Virus among South Korean Wild Boars in Areas near the Border with North Korea

“…The current circulating CSFV in Japan was identified moderate pathogenicity and most closely matched in nucleotide identity, with CSFVs recently isolated in China and Mongolia [8]. A space-time permutation analysis in Japan showed virus transmission spread (10.3 and 4.9 days/km) among wild boars in two significant clusters [9]. After overlaying of a map of habitat quality, approximately 82% and 75% of CSF notifications in two clusters were found in the areas with potential contact between pigs and wild boars [9].…”

“…Nevertheless, pig farms are also distributed in Hongcheon (Cluster III) and Chuncheon (east of Cluster II), and the risk of spread from wild boars to breeding pigs was present. In Japan, directional distribution of CSF notifications from September 2018 to June 2019 showed movement toward the northeast direction [9]. The 16 CSFVs from Korean wild boars spread from west to east between 2017 and 2019, and CSF sero-positive wild boars also showed similar pattern (west to east).…”

“…A high density of wild boars, particularly young wild boars, drives CSF outbreaks [7]. Recently, CSF have been reported in Gifu Prefecture, affecting domestic pigs and wild boars since September 2019 in Japan [8,9]. The current circulating CSFV in Japan was identified moderate pathogenicity and most closely matched in nucleotide identity, with CSFVs recently isolated in China and Mongolia [8].…”

“…A space-time permutation analysis in Japan showed virus transmission spread (10.3 and 4.9 days/km) among wild boars in two significant clusters [9]. After overlaying of a map of habitat quality, approximately 82% and 75% of CSF notifications in two clusters were found in the areas with potential contact between pigs and wild boars [9]. Monitoring of CSF in 5620 Korean wild boars captured between 2010 and 2014 identified only seven animals with CSFV and 23 animals with CSFV antibodies [10].…”

Development of a High-Throughput Serum Neutralization Test Using Recombinant Pestiviruses Possessing a Small Reporter Tag

“…In Japan, CSFV infection has spread among domestic pigs and wild boar since the first outbreak at a domestic pig farm in September 2018. Control of CSFV infection in wild boar should be prioritized for preventing the spread of CSF, because direct or indirect contact with wild boar infected with CSFV can be a primary route for the introduction of the virus to pig farms [33,34]. To prevent the spread of this infection in wild boar, an oral vaccination program targeting wild boar commenced in the spring of 2019.…”