How big is enough?

Le résumé fourni par la source

African swine fever (ASF) spreads among wild boar populations across Europe, but guidelines for defining the infectious buffer area (all reported cases plus a surrounding buffer where infected animals are likely to move) are largely uniform and rely on fixed-radius buffers or standardized frameworks, without explicitly accounting for spatial heterogeneity in habitat or wild boar movement ecology. We aimed to define buffer sizes to be applied around infected wild boar carcasses to support the delineation of infectious buffer areas. We analysed GPS data from 527 wild boar across 46 European study sites using a two-step approach combining first-passage time and Cox proportional hazard models to estimate the risk that wild boar leaves areas of different sizes (i.e. spatial scales). We investigated how the risk of leaving varied over time and across environmental gradients and used our model to provide a flexible, science-based tool to guide buffer sizing around infected wild boar carcasses, taking into account landscape composition and heterogeneity, rather than prescribing fixed values applicable in all situations. We found that the relationship between radius and risk of leaving is negative exponential and the risk of leaving increased over time, with a more rapid increase for smaller radii. Landscape homogeneity, terrain ruggedness and human pressure increased the risk of leaving, with stronger effects on small scales. Contrary to other predictors, the proportion of cropland exerted a strong effect on the risk of leaving at large spatial scales, especially at high levels of cropland. Across Europe, a buffer size of ~8 km is likely sufficient around most infection foci (i.e. infected wild boar carcasses, considering an infectious period of 14 days and a 5% probability that a wild boar leaves the area), but buffers up to 20 km may be necessary in certain areas to effectively limit the movement of wild boar. Synthesis and applications. Our results highlight the need for context-specific adaptive infectious buffer area. 8 km buffers around infected carcasses can limit the risk of infected wild boar dispersal but can be reduced to 5 km in highly heterogeneous landscapes or areas of high human impact. Larger buffers may be required in agricultural landscapes. We provide spatially explicit outputs (buffer sizes) that can directly inform policy and wildlife disease response strategies. The approach can be adapted to any other infectious disease.

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