Epidemiological considerations on African swine fever in Europe 2014–2018

Abstract

In 2007 African swine fever (ASF) arrived at a Black Sea harbour in Georgia and in 2014 the infection reached the European Union (EU), where it still expands its territory. ASF is a fatal viral disease affecting domestic pigs and wild boar of all ages with clinical presentations ranging from per-acute to chronic disease, including apparently asymptomatic courses. Until the detection of the first case inside the EU, infections in the current epidemic were mainly seen among pig farms with generally low biosecurity, and with incidental spill over to the wild boar population. In the EU, however, the infection survived locally in the wild boar population independently from outbreaks in domestic pigs, with a steady and low prevalence. Apart from the wild boar population and the habitat, the current epidemic recognizes humans as the main responsible for both long distance transmission and virus introduction in the domestic pig farms. This underlines the importance to include social science when planning ASF-prevention, −control, or -eradication measures.Based on experiences, knowledge and data gained from the current epidemic this review highlights some recent developments in the epidemiological understanding of ASF, especially concerning the role of wild boar and their habitats in ASF epidemiology. In this regard, the qualities of three epidemiological traits: contagiousity, tenacity, and case fatality rate, and their impact on ASF persistence and transmission are especially discussed.

Predicting spread and effective control measures for African swine fever– should we blame the boars?

“…Overall, this indicates that on average, the spread of ASF has a moving boundary due to wild boar movement of less than 25km in a year. This is in line with statistical analysis of the cases in Europe, with estimates of spread at a rate of 2-5km/month (Chenais et al 2019) and 1.5km/month (Podgórski and Śmietanka 2018). Our estimates, which are for spread by wild boar movement only, match the lower bounds of these statistical analyses.…”

“…In one study environmental transmission due to shedding of virus from infected live boar was found to be less than 3 days (Olesen et al 2018). Chenais et al (2019) state that ASF has been found experimentally to remain infectious in forest soil for 112 days. Further, Chenais et al (2019) mentioned another study in which soil samples from carcass locations were PCR-positive "several days or weeks after the carcasses has been removed although no viable virus could be isolated".…”

“…Chenais et al (2019) state that ASF has been found experimentally to remain infectious in forest soil for 112 days. Further, Chenais et al (2019) mentioned another study in which soil samples from carcass locations were PCR-positive "several days or weeks after the carcasses has been removed although no viable virus could be isolated". We therefore use a pert distribution of pert(3,14,112) days to describe the length of time that transmission is possible after skeletonisation.…”

“…Natural movement of wild boar, including both home range movement and long range dispersal, could lead to contact of infected boar with susceptible boar and pigs in uninfected areas, thus spreading the disease away from the initial source. For transmission to pigs it is considered more likely that human-mediated transmission has been involved (Chenais et al 2019) as direct contact between boar and pigs will be very low if sufficient biosecurity is in place. Long-distance jumps of the disease have also occurred, such as the cases in Czech Republic and Belgium which were several hundred kilometres away from the nearest case (EFSA et al 2018), and these are very unlikely to have occurred due to natural wild boar movement.…”

“…Long-distance jumps of the disease have also occurred, such as the cases in Czech Republic and Belgium which were several hundred kilometres away from the nearest case (EFSA et al 2018), and these are very unlikely to have occurred due to natural wild boar movement. Human-mediated pathways are thought most likely to have led to those cases, with human transportation of infected meat perhaps most probable, although contaminated trucks, and movement of infected pigs, boar or boar carcasses are also possible transmission routes (EFSA et al 2018, Chenais et al 2019.…”