The effect of woodland expansion on tick populations and Lyme disease risk
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Date
2021
Publication Type
Doctoral Thesis
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Abstract
Woodland expansion through natural regeneration and planting projects is occurring in Europe. While woodland expansion is expected to deliver different ecosystem services, including enhanced biodiversity and carbon sequestration, it can also lead to the ecosystem disservice of emerging disease risk from ticks. Notably, Lyme disease, caused by the bacterial complex Borrelia burgdorferi sensu lato (s.l.). has been reported to have increased in the past decades in Europe and in Scotland. It has repeatedly been demonstrated that woodlands harbour more ticks and higher Lyme disease hazard than open land, but there is a gap in research on the effect of different landscape management choices i.e. the type and age of woodlands as well as deer management regimes on tick populations and Lyme disease risk.
• In this thesis, I adopt an interdisciplinary approach across ecology and the social sciences to understand the effect of woodland expansion on tick populations and Lyme disease risk in Wester Ross in the Scottish Highlands, an area undergoing rapid woodland expansion. Although Wester Ross is scarcely populated, a large portion of the local population work and/or recreate outdoors and it is a popular area with tourists. Through four studies, I 1) reveal the prevalence of different non-viral pathogens in ticks in Wester Ross, and compare this prevalence with other areas in the UK and The Netherlands 2) shed light on the effect of woodland type and age and deer management regimes on tick populations and Lyme disease hazard 3) quantify ticks on deer to understand the role of deer in the tick cycle and their potential role in the B. burgdorferi transmission cycle and 4) provide insights on local people’s exposure, knowledge and perception on ticks and Lyme disease.
• For the execution of the studies, we carried out fieldwork in Wester Ross in the Scottish Highlands to quantify tick, deer and rodent populations in five different land cover types: open heather moorland, young Scots pine woodlands, mature Scots pine woodlands, mature birch woodlands and mature Sitka spruce plantations. We also quantified ticks of all life stages on entire deer carcasses and ear and inguinal samples. Finally, we carried out interviews with local recreationists and local outdoor professionals on their exposure to, knowledge of and perceptions on ticks. Molecular analysis of a subset of the ticks was undertaken for the detection of eight pathogen groups, namely Anaplasma phagocytophilum, B. burgdorferi sensu lato (s.l.), Babesia from clade X, Rickettsia helvetica, Spiroplasma ixodetis, Neoehrlichia mikurensis, Borrelia miyamotoi and Babesia microti. Molecular analysis of all the ticks was carried out to detect B. burgdorferi s.l. and genospecies.
• Results showed that 1) ticks harbour different pathogens of zoonotic importance, namely A. phagocytophilum (4.7% prevalence), B. burgdorferi sensu lato (s.l.) (2.2%), Babesia from clade X (0.2%), R. helvetica (0.04%), and S. ixodetis (0.4%) and the latter was discovered for the first time in Great Britain 2) tick densities are higher in mature natural woodlands (pine and birch) than unwooded land, but tick densities and Lyme disease hazard can be mitigated through deer management (fencing and/or culling) 3) deer carry ticks of all life stages year-round and 4) local people are highly aware of ticks and associated risks as well as the environmental factors that influence ticks, but do not always use protective measures before going outdoors. Their opinions on tick mitigation measures are influenced by the general land use debate in Scotland on woodland expansion and deer management.
• The findings are detailed and discussed in four main chapters. Together, they aim to contribute to our understanding of the effect of woodland expansion on Lyme disease risk from both an ecological and a social perspective and thus helps to understand present and future risks from ticks and what mitigation measures can be adopted against these risks, while considering local perceptions on ticks and Lyme disease risk.
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Examiner: Ghazoul, Jaboury
Examiner : Gilbert, Lucy
Examiner : Metzger, Marc J.
Examiner : Birtles, Richard
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ETH Zurich
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Subject
ticks; disease ecology; Lyme disease; reforestation; Scotland
Organisational unit
03723 - Ghazoul, Jaboury / Ghazoul, Jaboury