When to kill a cull: factors affecting the success of culling wildlife for disease control

Abstract

<jats:p>Culling wildlife to control disease can lead to both decreases and increases in disease levels, with apparently conflicting responses observed, even for the same wildlife–disease system. There is therefore a pressing need to understand how culling design and implementation influence culling's potential to achieve disease control. We address this gap in understanding using a spatial metapopulation model representing wildlife living in distinct groups with density-dependent dispersal and framed on the badger–bovine tuberculosis (bTB) system. We show that if population reduction is too low, or too few groups are targeted, a ‘perturbation effect’ is observed, whereby culling leads to increased movement and disease spread. We also demonstrate the importance of culling across appropriate time scales, with otherwise successful control strategies leading to increased disease if they are not implemented for long enough. These results potentially explain a number of observations of the dynamics of both successful and unsuccessful attempts to control TB in badgers including the Randomized Badger Culling Trial in the UK, and we highlight their policy implications. Additionally, for parametrizations reflecting a broad range of wildlife–disease systems, we characterize ‘Goldilocks zones’, where, for a restricted combination of culling intensity, coverage and duration, the disease can be reduced without driving hosts to extinction.</jats:p>

Hunting alters viral transmission and evolution

“…S8/S9). The lack of signal from prevalence data may be a contributing factor behind the variability of the effects of hunting on disease dynamics in empirical systems 40 . Prevalence data may be better able to detect shifts in population demography where the pathogen causes acute infections with shorter periods of immunity.…”

A systemic approach to assess the potential and risks of wildlife culling for infectious disease control

“…For other infectious diseases, the transmission risk . A buffer around the culling area is often defined to alleviate edge effects, for instance, the impact of survivors migrating outside the culling area 75 . The size of the culling and buffer areas together is the same as that of the control area.…”

“…Depending on the initial prevalence and incidence rates in a population, different scenarios are modeled by varying parameters, such as the population reduction rate and the cull duration and frequency. The model that maximizes the likelihood of pathogen local extinction is selected 75 . However, such approaches are typically hampered by the limited knowledge of the eco-epidemiological system and transmission processes 76 .…”

“…Culling effects go beyond the simple reduction of the population numbers. Animal territoriality is often affected by culling, with crucial consequences on the epidemiology of the targeted pathogen, as recently modeled by Prentice et al 75 . The behavioral response of badgers to culling in the UK (see Box 2) included increased dispersal within the culled areas.…”

Behavioural ecology and infectious disease: implications for conservation of biodiversity

“…Culling was used to control badger populations but also destabilized their territories, which led to immigration into the culled area, greater overlap in ranges, and less stable range boundaries [82]. This destabilizing effect can increase disease prevalence if the rate, duration and spatial extent of culling are inadequate to properly control the population [82,83]. An area for future research is to model the effects of culling and vaccination regimes that apply knowledge of territorial behaviour to dynamic social networks.…”