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

Studentship strategic priority area:Environment, pollution and human health
Keywords: biodiversity, zoonosis, infectious disease, vector, Lyme disease

Abstract:

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), 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.