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

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.

A Critical Review about Different Vaccines against Classical Swine Fever Virus and Their Repercussions in Endemic Regions

“…The causative agent is a highly contagious, small, enveloped, single-stranded RNA virus known as CSF virus (CSFV), which together with other 11 viral species comprise the Pestivirus genus of the family Flaviviridae [3]. Since CSF-outbreaks have negative social and economic implications, including serious restrictions on international trade of pigs and their products, high financial burden due to direct or indirect loses in the pig industry, and the ethical aspects linked to the removal of herds in affected farms, it is considered a notifiable pathogen by the World Organiza-Asia, such as Japan [10] and South Korea [11], sheds light about the serious concern that a potential global reemergence of this disease represents.…”

Quantitative Understanding of the Decision-Making Process for Farm Biosecurity Among Japanese Livestock Farmers Using the KAP-Capacity Framework

“…The SRHM provided clear guidance to Japanese livestock farmers regarding biosecurity; however, compliance remains a challenge ( 18 ). The recent incursion of classical swine fever into the wild boar population has been causing infections on Japanese pig farms since 2018 ( 19 , 20 ), and thus, improvements in farm biosecurity are becoming increasingly important.…”

Classical Swine Fever: A Truly Classical Swine Disease

“…At this difficult period, Pathogens has the timely honor to present a Special Issue on Classical Swine Fever collecting 14 publications. Readers can find that perhaps few swine diseases have such a comparable ancient history as CSF [ 1 ], and few have such a versatile capability in affecting so many body systems [ 1 ] via horizontal [ 2 , 3 ] as well as vertical [ 4 , 5 ] transmissions. And few have so many clinical forms expressed, ranging from acute to chronic, atypical to congenital, etc.…”

“…The CSF world has been quiet for almost 20 years [ 6 ]. It was until the year 2018, when a reemergence from previously CSF-free Japan [ 2 , 3 ] raised our attention. The reemergence was largely attributed to the virus hidden in wild boar populations and transmitted, by direct or indirect contact, to neighboring domestic herds.…”

“…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 ].…”