Modelling Spatial and Temporal Patterns of African Swine Fever in an Isolated Wild Boar Population to Support Decision-Making.

Simon Croft,Graham C Smith,James N Aegerter,Giovanna Massei,David Fouracre

doi:10.3389/fvets.2020.00154

Simon Croft, Graham C Smith + Show 3 more

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https://doi.org/10.3389/fvets.2020.00154

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Abstract

African swine fever (ASF) is a highly contagious disease affecting all suids including wild boar. As the disease can damage commercial pig production and its circulation can threaten international trade, understanding the risks produced by free-living wild boar (as a wildlife reservoir) is important to ensure proportionate policies to exclude the disease, as well as an effective contingency response. The recent spread of the virus into Western Europe has produced concerns in many stakeholders including pig producers and national governments. Unlike in mainland Europe, where wild boar are widespread, in Britain, free-living populations have only recently re-established, and whilst these are still relatively small and isolated, they may provide a sufficient reservoir capable of sustaining disease and may thus present a continual source of infection risk to domestic pigs. This study focuses on one component of the risk produced by wild boar, specifically the distribution and persistence of virus in a landscape produced by the natural circulation of disease within wild boar. We used a spatial individual-based model run across a representation of a real landscape to explore the epidemiological consequences of an introduction of ASF into the Forest of Dean, currently hosting the largest population of wild boar in England. We explore various scenarios including variations in the prophylactic management of boar, as well as variations in reactive management (contingency response) following the detection of disease to evaluate their value in reducing this specific risk (presence of ASF virus of wild boar origin in the landscape). The abundance and distribution of wild boar is predicted to increase across our study extent over the next 20 years. Outbreaks of ASF are not predicted to be self-sustaining, with the median time to disease “burn-out” (no new infections) being 14 weeks. Carcass removal, as a tool in a package of reactive management, was of limited value in reducing the duration of outbreaks in this study. We suggest that useful predictions of some of the risks produced by ASF might be possible using only the distribution of the boar, rather than more difficult abundance or density measures.

Highlights

African swine fever (ASF) is a highly contagious and virulent disease of suids, known to severely damage commercial pig production and infect free-living wild boar in Europe [1]. It is recognized by the World Organization for Animal Health (OIE) as a notifiable disease and its circulation has an impact on international trade
To better understand the risks to commercial pig production posed by the incursion of ASF into a free-living population of wild boar in England we developed a spatially explicit individual-based model (IBM) and used it to predict the course of disease in wild boar and explore the value of different prophylactic and reactive management actions to mitigate the risk
With moderate hunting (p. hunted = 0.0065), equal to the estimated culling rate in the FC estate [i.e., ∼45% of the population removed per year [15]], our results showed that wild boar populations would still grow but at a slower rate, reaching nearly 4,000 individuals occupying 300 km2 in the same 20 year period

Summary

Introduction

African swine fever (ASF) is a highly contagious and virulent disease of suids, known to severely damage commercial pig production and infect free-living wild boar in Europe [1]. It is recognized by the World Organization for Animal Health (OIE) as a notifiable disease and its circulation has an impact on international trade. There is, considerable interest in detailed assessments of the risks posed by this disease to help countries prepare for its incursion, and the required contingency responses These responses include those affecting commercial pig farms, as well as back-yard producers rearing small herds and some interventions produce an economic burden per se; limiting the duration of these controls is of economic interest. Such policies should be proportionate and practical [2], following available guidelines [3, 4] and should be based on the best available science [5, 6]

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