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

Abstract

There has been a rapid increase in the number of classical swine fever (CSF) sero-positive wild boars captured near the demilitarized zone (DMZ), located the border with North Korea. In 2015–2016, few CSFV-positive antibody boars were detected; however, the number has increased steeply since 2017. Most occurred in the northern region of Gyeonggi before spreading slowly to Gangwon (west to east) in 2018–2019. Multi-distance spatial cluster analysis provided an indirect estimate of the time taken for CSFV to spread among wild boars: 46.7, 2.6, and 2.49 days/km. The average CSF serum neutralization antibody titer was 4–10 (log 2), and CSFV Ab B-ELISA PI values ranged from 65.5 to 111.5, regardless of the age and sex of wild boars. Full genome analysis revealed that 16 CSFV strains isolated from wild boars between 2017 and 2019 were identical to the YC16CS strain (sub-genotype 2.1d) isolated from an outbreak in breeding pigs near the border with North Korea in 2016. The rapid increase in CSF in wild boars may be due to a continuously circulating infection within hub area and increased population density. The distribution pattern of CSFV in Korean wild boars moves from west to southeast, affected by external factors, including small-scale hunting, geographical features and highways.

Genetically distinct pestiviruses pave the way to improved classical swine fever marker vaccine candidates based on the chimeric pestivirus concept

“…Cross-reactivity is likely to occur, although not reported in a study investigating seroconversion in a limited number of animals [ 11 ]. The use of CSF marker vaccines in domestic pigs and bait vaccination of wild boar in South Korea just started very recently [ 12 ]. It will be of great interest to learn how robust this DIVA concept works under field conditions.…”

“…In this CSFV chimera, the complete E rns and signal peptide encoding sequence was replaced by corresponding BVDV sequences [ 11 ]. The vaccine was licensed in South Korea in 2017 and can be applied in domestic pigs as well as in wild boar [ 12 ]. In China, an inactivated vaccine based on a recombinant baculovirus expressing the CSFV E2 protein has been licensed in 2017 and is used by some pig farms [ 13 ].…”

Epidemiology of Classical Swine Fever in Japan—A Descriptive Analysis of the Outbreaks in 2018–2019

“…Subgenotype 2.1d was firstly isolated from the outbreaks in China in 2014 to 2015 (8) and is reported to cause a chronic or moderate form of infection (9)(10)(11). It has also been detected in South Korea (12,13). A phylogenetic study showed that the CSF virus isolated from the 2018 Japan outbreak index case was different from the strains that had caused previous CSF-outbreaks in Japan (6).…”

Classical Swine Fever: A Truly Classical Swine Disease

“…The spread of CSF followed the migration paths of wild boars. The same concern also goes to wild boar populations residing in the demilitarized zone of Korea [ 7 ]. The spatial distance between each CSF notification was about 23 km, the widest radius of outbreak cluster was 20 km [ 2 ], and each outbreak cluster lasted 98–124 days [ 2 ].…”

“…These data provide a scientific basis on how far and how long the control measure should be imposed. Monitoring the antigen and antibody in wild boars will provide warning for neighboring domestic pigs in those particular settings [ 3 , 7 ].…”