Abstract
African swine fever (ASF) is a devastating viral disease of swine that is present in both pigs and wild boar in the western part of the Russian Federation and the eastern part of the European Union. It represents a significant threat for the European pig production industry as neither treatment nor vaccine is available. This study analysed the spatial and spatio-temporal distributions of ASF cases that were reported in domestic pigs and wild boar for assessing the likelihood of wild boar-to-domestic pig and farm-to-farm transmission routes in the epidemic that occurred from 2007 to 2014 in the Krasnodar and the Tver regions, two of the most affected areas of the Russian Federation. Results suggest that in both regions, the spatial proximity to an infectious farm was a strong risk factor for infection of a susceptible farm. In the Krasnodar region, the results of the statistical analysis suggest that the epidemics in wild boar and in domestic pigs were independent from each other. In contrast, there seemed to be a dependence between the two epidemics in the Tver region. But because outbreaks in domestic pigs were not statistically significantly clustered around wild boar cases, the joint spatial distribution of wild boar cases and of outbreaks in domestic pigs in the Tver region may be explained by regular spillovers from the domestic pig to the wild boar population. These findings confirm the need to maintain high biosecurity standards on pig farms and justify strict control measures targeted at domestic pig production such as culling of infected herds and local movement restrictions.
Highlights
African swine fever (ASF) is a viral disease of swine associated with a case fatality rate that can reach 100% depending on the strain
The aim of the study was to explore the relative importance of the routes of transmission of ASF that could be responsible for the local spread of the disease as observed in the Krasnodar and the Tver regions
In the Krasnodar region, there was no statistical spatial dependence between the epidemics in wild boar and in domestic pigs (Table 2) and, consistently, the risk of infection of settlements did not increase with decreasing distance from wild boar cases (Figure 4)
Summary
African swine fever (ASF) is a viral disease of swine associated with a case fatality rate that can reach 100% depending on the strain. The virus spread throughout the whole country, crossed the Caucasus probably via infected wild boar (Sus scrofa) and entered the Russian Federation in late 2007. Whilst the first detection of an infected wild boar occurred in November 2007, the first report of an outbreak in domestic pigs was published seven months later, in June 2008. From 2007 to 2010, the virus circulated only in the southern regions of the Russian Federation affecting both domestic pigs and wild boars. In early 2011, the virus was introduced into central and northern regions where it subsequently spread locally resulting in new clusters of outbreaks and an increased risk of introduction for the European Union (Figure 1). 333 outbreaks in domestic pigs and 137 wild boar cases have been detected and reported in the Russian Federation (source: EMPRES-i, accessed October 2014)
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