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Epidemiological analysis of African swine fever in the European Union (September 2019 to August 2020)

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Abstract

An update on the African swine fever (ASF) situation in the 10 affected Member States (MS) in the EU and in two neighbouring countries from the 1 September 2019 until the 31 August 2020 is provided. The dynamics of the proportions of PCR‐ and ELISA‐positive samples since the first ASF detection in the country were provided and seasonal patterns were investigated. The impact of the ASF epidemic on the annual numbers of hunted wild boar in each affected MS was investigated. To evaluate differences in the extent of spread of ASF in the wild boar populations, the number of notifications that could be classified as secondary cases to a single source was calculated for each affected MS and compared for the earliest and latest year of the epidemic in the country. To evaluate possible risk factors for the occurrence of ASFV in wild boar or domestic pigs, a literature review was performed. Risk factors for the occurrence of ASF in wild boar in Romanian hunting grounds in 2019 were identified with a generalised linear model. The probability to find at least one PCR‐confirmed ASF case in wild boar in a hunting ground in Romania was driven by environmental factors, wild boar abundance and the density of backyard pigs in the hunting ground area, while hunting‐related variables were not retained in the final model. Finally, measures implemented in white zones (ASF‐free zones that are geographically adjacent to an area where ASF is present in wild boar) to prevent further spread of ASF were analysed with a spatially, explicit stochastic individual‐based model. To be effective, the wild boar population in the white zone would need to be drastically reduced before ASF arrives at the zone and it must be wide enough. To achieve the necessary pre‐emptive culling targets of wild boar in the white zone, at the start of the establishment, the white zone should be placed sufficiently far from the affected area, considering the speed of the natural spread of the disease. This spread is faster in denser wild boar populations. After a focal ASF introduction, the white zone is always close to the infection hence pre‐emptive culling measures in the white zone must be completed in short term, i.e. in a few months.

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