Does urbanisation and urban heat impact parasite burden and disease risk from the invasive grey squirrel in the UK?

As urban centres expand globally, wild animal populations become exposed to a range of new anthropogenic stressors including pollution which may reduce immunocompetence and increase disease susceptibility. Urban areas are also often the epicentre for the introduction of invasive host species that can carry zoonotic diseases. For example, in the UK ticks found in the invasive grey squirrel (Sciurus carolinensis) can carry Borrelia bacteria which cause Lyme disease.

Invasive species can increase zoonotic disease risk by increasing the abundance of existing pathogens and parasites as well as introducing new ones into the environment and facilitating transmission. However, the relationship between urban-related stress on the immunocompetence of invasive host species and zoonotic disease risk is still not fully understood.

This interdisciplinary project will address this knowledge gap studying populations across the urban-rural gradient in the UK to quantify how urban stress affects grey squirrel immunocompetence, tick ectoparasite burden, and ultimately Lyme disease risk. Bringing together an array of approaches and data we aim to describe how urbanisation impacts host-parasite dynamics and develop a predictive model to map and forecast disease risk.

The student will specifically address four goals/proposed thesis chapters: 1. Characterise the prevalence of Borrelia-carrying ticks in grey squirrels living across an urbanization gradient.

2. Identify the environmental, ecological and urban-specific drivers of the spatial distribution of infected hosts and ectoparasites. 3. Quantify the levels of stress and immunocompetence in grey squirrels living across the urbanization gradient. 4. Model and map grey squirrel infection risk across urban landscapes.

1c. What novel concepts, approaches, or methodology will the project develop? What are important challenges and limitations? (Avoid jargon or specialist knowledge; must keep under 250 words) Novelty in this project comes from -

Study design: studying populations along an urbanisation gradient, rather than comparing rural vs urban populations, offers the opportunity to unveil factors influencing parasite-host dynamics at a finer resolution and non-linear relationships and thresholds. Working across a gradient could be a challenge for data collection but we already have a large existing tissue biobank of grey squirrel samples and work closely with teams doing squirrel management (culling) across the UK.

Data integration: this project will bring together spatial environmental data with individual-level host level data on health, immunity, and parasite/disease load. Environmental data will be obtained from available sources (e.g., Landsat, UK AIR, Met Office, the London Atmospheric Emissions Inventory). Post-mortem examinations will allow the collection of data regarding exposure to urban-related pollutants, parasite, and disease load as well as blood/tissue collection for health, stress, and immunity assays. Expertise with the data and approaches in the supervisory team will facilitate this integration.

Modelling: We propose to develop a new spatially explicit model of disease risk that describes how changes in urbanization relate to host condition and ectoparasite/disease prevalence. This model will be used to map and predict Lyme disease risk across an urbanization gradient. We will also explore the development of an urbanisation index that could be used beyond this system and the implementation of a user-friendly interface mapping risk to support prevention and public awareness.

The challenges associated with potential biases in sampling and spatial autocorrelation will be reduced by the institutional and supervisory expertise in these topics.