RCG One Health approach to tick-borne disease control through manipulation of reservoir host communities at landscape scale

The UK's Net Zero 2050 policy contains bold plans to plant millions of trees each year to expand landcover in woodlands and forests, not only helping to sequester carbon but also helping to lower local temperatures as the climate changes. While this is a valid ambition, such changes in land use may have implications for the spread of unwanted non-native species and disease. As such these plans must be evaluated to develop a robust strategy and avoid unintended consequences from our interventions to mitigate climate change and achieve a net zero society.

The grey squirrel is an invasive species in the UK, with detrimental impacts on the conservation of the native red squirrel and with bark stripping damage to trees and forests that is estimated to cost the UK economy £37 million per year. Grey squirrels, now distributed through most of Great Britain, are the dominant small mammal in many habitats and important hosts of ticks that feed on them. The ticks that feed on grey squirrels can pick up infections in the squirrel's blood and can transmit these infections to people bitten by infected ticks, notably Lyme disease. The number of people contracting Lyme disease is growing in all parts of the UK, with hotspots in Scotland, the southwest of England and southern England. Efforts to control grey squirrels are under way in many parts of the UK, to help the native red squirrel populations which are under threat by greys. This programme has wide public support and is trying to control grey squirrels humanely using contraceptives. Some experts have argued that the removal of grey squirrels by itself could result in a reduction in Lyme disease risk, but this has not yet been proven. This is because other wild animals can be fed upon by ticks, and it is not clear what will happen when grey squirrels are removed in terms of disease risk. Our project plans to answer this question by determining what happens when grey squirrel populations are being reduced, and how this affects ticks and diseases. We plan to look at novel ways of controlling or monitoring ticks by determining what attracts and repels them. We also plan to develop predictive models on what would happen as the UK becomes more covered in woodlands and forests in the future where climate is also changing, and what this would mean for grey squirrel populations, and the ticks and diseases they host. Finally we plan to engage with the public, particularly those trying to save the red squirrel, but also the wider public and their attitudes towards squirrels, ticks and infections such as Lyme disease to ensure we understand people's concerns and how best to deal with a changing environment and climate.

Research will help ensure there are no unintended consequences from policies aiming to reforest the UK, which may favour invasive species such as the grey squirrel and increase the spread of tick-borne diseases. Activities will answer whether reducing the population of grey squirrels has an impact on Lyme disease prevalence. As there are knowledge gaps on ecological relationships among hosts, ticks and pathogens, we will collect molecular microbiological information from tick blood meals and assess how the dynamics of host feeding change when grey squirrel populations are reduced. We plan an empirical study that collects squirrel and tick samples in squirrel populations undergoing culling or fertility control and undisturbed populations to assess prevalence of Borrelia burgdorferi. As part of our multidisciplinary approach, we will use a range of social science methods to produce a deeper understanding of public knowledge and attitudes around issues of reforesting and awareness about Lyme disease and ticks in the context of environmental and public health. We will target tick chemical and behavioural ecology using gas-chromatography linked single sensillum electrophysiology to identify squirrel odours that trigger tick responses. This will be followed by behavioural bioassays aiming to discover host masking odours. Data collected will be used to extend existing models developed to simulate the management of grey squirrels to incorporate dynamics of tick vectors and other host species involved in the spread of Lyme disease. Developing future scenarios incorporating strategies for future land use change, changes to distribution, abundance, and behaviour of animals, and information about public attitudes to control, we will use this model to explore potential risk of Lyme disease on public health. These outputs will be targeted to inform policy decision-making in regard to both potential wildlife management and land use strategy.