African swine fever in wild boar

Abstract

The European Commission requested EFSA to compare the reliability of wild boar density estimates across the EU and to provide guidance to improve data collection methods. Currently, the only EU-wide available data are hunting data. Their collection methods should be harmonised to be comparable and to improve predictive models for wild boar density. These models could be validated by more precise density data, collected at local level e.g. by camera trapping. Based on practical and theoretical considerations, it is currently not possible to establish wild boar density thresholds that do not allow sustaining African swine fever (ASF). There are many drivers determining if ASF can be sustained or not, including heterogeneous population structures and human-mediated spread and there are still unknowns on the importance of different transmission modes in the epidemiology. Based on extensive literature reviews and observations from affected Member States, the efficacy of different wild boar population reduction and separation methods is evaluated. Different wild boar management strategies at different stages of the epidemic are suggested. Preventive measures to reduce and stabilise wild boar density, before ASF introduction, will be beneficial both in reducing the probability of exposure of the population to ASF and the efforts needed for potential emergency actions (i.e. less carcass removal) if an ASF incursion were to occur. Passive surveillance is the most effective and efficient method of surveillance for early detection of ASF in free areas. Following focal ASF introduction, the wild boar populations should be kept undisturbed for a short period (e.g. hunting ban on all species, leave crops unharvested to provide food and shelter within the affected area) and drastic reduction of the wild boar population may be performed only ahead of the ASF advance front, in the free populations. Following the decline in the epidemic, as demonstrated through passive surveillance, active population management should be reconsidered.

Keywords: African swine fever; passive surveillance; population density; population density threshold; population reduction; population separation; wild boar.

Figure 1

Numbers of wild boar harvested in the hunting grounds in the EU Member States in 2017

Figure 2

Wild boar population trends in Europe since 1990. The lines represent standardised wild boar hunting bags for currently unaffected (blue) and affected (orange) countries. Each annual index is calculated in relation to the first observation, which is arbitrarily set at 1, thus standardising population trends

Figure 3

Wild boar management after a local African swine fever (ASF) outbreak in the Czech Republic

1. (A) Panel A shows a schematic overview of the management areas at the beginning of the outbreak. The scheme visualises only the logical order and naming of the areas. The relative size is not meant to reflect the real geographic situation.

   (B) Panel B shows all the areas in the real geographic context.

   (C) Localisation of positive wild boar. Some positive cases were found outside of fenced area; however, they were still in the high‐risk area (red area in Figure 3). In the low‐risk area (green area, Figure 3) or the intensive hunting area (yellow area, Figure 3), there were no positive results yet.