Identifying Environmental Risk Factors for Louping Ill Virus Seroprevalence in Sheep and the Potential to Inform Wildlife Management Policy.

Lucy Gilbert,Kim Willoughby,Chris Cousens,Franz Brülisauer

doi:10.3389/fvets.2020.00377

Lucy Gilbert, Kim Willoughby + Show 2 more

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https://doi.org/10.3389/fvets.2020.00377

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Abstract

Identifying the risk factors for disease is crucial for developing policy and strategies for controlling exposure to pathogens. However, this is often challenging, especially in complex disease systems, such as vector-borne diseases with multiple hosts and other environmental drivers. Here we combine seroprevalence data with GIS-based environmental variables to identify the environmental risk factors associated with an endemic tick-borne pathogen—louping ill virus—in sheep in Scotland. Higher seroprevalences were associated with (i) upland/moorland habitats, in accordance with what we predicted from the habitat preferences of alternative LIV transmission hosts (such as red grouse), (ii) areas of higher deer density, which supports predictions from previous theoretical models, since deer are the key Ixodes ricinus tick reproduction host in this system, and (iii) a warmer climate, concurring with our current knowledge of how temperature affects tick activity and development rates. The implications for policy include adopting increased disease management and awareness in high risk habitats and in the presence of alternative LIV hosts (e.g., grouse) and tick hosts (especially deer). These results can also inform deer management policy, especially where there may be conflict between contrasting upland management objectives, for example, revenue from deer hunting vs. sheep farmers.

Highlights

Identifying the risk factors for disease is crucial for developing policy and strategies for controlling exposure to pathogens
The most complex disease systems are those with both multiple vector hosts and multiple pathogen transmission hosts, which makes disease risk difficult to predict and to control, and it is challenging to tease apart the effect of the livestock themselves from wildlife or other environmental factors on disease risk
There was no association between louping ill virus (LIV) within-flock seroprevalence and the proportion of land cover that was blanket bog, bracken, montane, coarse grassland or woodland, nor sheep or cattle density, northing, easting, or time of year, or year the blood sample was taken; all these variables were removed from the model during the backwards stepwise procedure

Summary

Introduction

Identifying the risk factors for disease is crucial for developing policy and strategies for controlling exposure to pathogens. In Europe these pathogens are vectored primarily by the most ubiquitous tick in Europe, Ixodes ricinus, which is a generalist, parasitizing almost all terrestrial vertebrates It spends the vast majority of its lifecycle away from its hosts, so its survival and activity is influenced by a multitude of environmental factors [e.g., [6,7,8,9,10]]. LIV is much less studied than B. burgdorferi s.l., and, while not as complex a system, still has multiple transmission hosts including birds and mammals It causes illness and death in livestock, especially sheep Ovies aries [11], and in red grouse Lagopus lagopus scoticus [12], an economically valuable gamebird. A national scale analysis of environmental risk factors for LIV infection in sheep has not, until now, been conducted

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