Managing landscapes for conservation and human health: the role of deer and non-native hedgehogs in tick-borne disease emergence in the Western Isles

As biological communities change, for example because species are added, lost, or become more abundant, this changes
how species interact. Altered species interactions can be negative from a human point of view, such as when modified
communities provide better conditions for dangerous pathogens to circulate and to be transmitted to the human host. This
project investigates this problem on the islands of Uist, in the western Isles of Scotland.
Two mammal species, the European hedgehog and red deer, have become much more abundant on the Uists than they
historically were. Hedgehogs are not native to the islands but were introduced several times since the 1970s. Since then,
they have become highly abundant and are causing serious problems by predating on ground nesting birds. Red deer have
also increased markedly in abundance over the past decades. Over the same time, ticks and human cases of Lyme
disease, which is caused by the bite of an infected tick, have increased on the Uists to a level that is much higher than on
neighbouring islands or on the Scottish mainland. The increase in ticks is most likely linked to that in deer, since deer are
known to support high numbers of ticks, but deer are not able to transmit Borrelia, the bacterial agent causing Lyme
disease. Hedgehogs on the other hand can carry high tick burdens and are commonly infected with Borrelia. This makes it
probable that hedgehogs, along with native small mammals, are playing a role in the maintenance and current rise in ticks
infected with Borrelia. We therefore hypothesise that it is the combination high deer and high hedgehog numbers that is
causing an increased risk of Lyme disease in this system.

Our project will test this hypothesis and provide much needed information for management by forging an interdisciplinary
team of academic researchers, conservation groups, tick specialists, and public health officials. The project will run over
four years and has three major aims: First, we will test how the spatial distribution and abundance of deer relates to the
density of questing ticks and Lyme disease risk. We will sample ticks in the environment across the full range of deer
densities found on the Uists, and test what proportion is infected with the pathogen. Secondly, we will establish the role of
introduced hedgehogs as hosts for ticks and tick-borne diseases by live-trapping and sampling hedgehogs (and native
small mammals) for ticks, which are also tested. Thirdly, we will incorporate our field data into mathematical models to
examine what effect the removal of hedgehogs and deer is predicted to have on Lyme disease risk.
This work represents a unique partnership between the University of Glasgow, Scottish Natural Heritage (providing advice
to the Scottish Government), the James Hutton Institute, and the National Health Service - Western Isles. Working jointly
will ensure that our research addresses the needs of the different partners and that data and findings are shared efficiently
among all of them. In addition, we will work closely with local land managers, organisations, and communities to make sure
that they are equally able to benefit from this work. Our project will be an excellent opportunity to test important ecological
hypotheses and to influence land management with the aim of reducing the risk of tick-borne disease.