Managing African Swine Fever: Assessing the Potential of Camera Traps in Monitoring Wild Boar Occupancy Trends in Infected and Non-infected Zones, Using Spatio-Temporal Statistical Models.

Martijn Bollen,Maxime Fajgenblat,Thomas Neyens,Jim Casaer,Alain Licoppe,Benoît Manet,Natalie Beenaerts,Valérie De Waele

doi:10.3389/fvets.2021.726117

Abstract

The recent spreading of African swine fever (ASF) over the Eurasian continent has been acknowledged as a serious economic threat for the pork industry. Consequently, an extensive body of research focuses on the epidemiology and control of ASF. Nevertheless, little information is available on the combined effect of ASF and ASF-related control measures on wild boar (Sus scrofa) population abundances. This is crucial information given the role of the remaining wild boar that act as an important reservoir of the disease. Given the high potential of camera traps as a non-invasive method for ungulate trend estimation, we assess the effectiveness of ASF control measures using a camera trap network. In this study, we focus on a major ASF outbreak in 2018–2020 in the South of Belgium. This outbreak elicited a strong management response, both in terms of fencing off a large infected zone as well as an intensive culling regime. We apply a Bayesian multi-season site-occupancy model to wild boar detection/non-detection data. Our results show that (1) occupancy rates at the onset of our monitoring period reflect the ASF infection status; (2) ASF-induced mortality and culling efforts jointly lead to decreased occupancy over time; and (3) the estimated mean total extinction rate ranges between 22.44 and 91.35%, depending on the ASF infection status. Together, these results confirm the effectiveness of ASF control measures implemented in Wallonia (Belgium), which has regained its disease-free status in December 2020, as well as the usefulness of a camera trap network to monitor these effects.

Highlights

African swine fever (ASF), a viral disease that causes high mortality among domestic pigs (Sus scrofa domesticus) and wild boar (Sus scrofa), originates from East Africa and is regarded as one of the most important threats to the European pig industry
We suggest that the main effect at play is a density-dependent effect [32, 33], a decline in detection probability governed by a decreasing wild boar density
We conclude that ASF infection status was the main driver of wild boar occupancy at the beginning of the monitoring period, which led to higher occupancies in the ASF-infected zone compared to the non-infected zone

Summary

Introduction

African swine fever (ASF), a viral disease that causes high mortality among domestic pigs (Sus scrofa domesticus) and wild boar (Sus scrofa), originates from East Africa and is regarded as one of the most important threats to the European pig industry. Management strategies include continuous carcass removal from the infected zone, coupled with intense culling of wild boar within a buffer zone [5] Together, these strategies are expected to effectively reduce ASF transmission by removing viral sources from the environment in the infected zone and by depleting the susceptible wild boar population in the buffer zone. These strategies are expected to effectively reduce ASF transmission by removing viral sources from the environment in the infected zone and by depleting the susceptible wild boar population in the buffer zone The latter is essential, since the number of individuals remaining in the host population of the buffer zone will determine the probability of the spread to a non-infected area, i.e., host threshold density. To evaluate measures aimed at counteracting ASF, sound information on the joint effect of the disease and culling efforts on population trends of wild boar within the managed areas is crucial [3]

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