Master Thesis

Comparing prevalence of Borrelia burgdorferi s.l. among Ixodes ricinus ticks in urban, suburban, and natural habitats across Europe: A meta-analysis

Christoffer Johansson (10/2022-04/2023)

Support: Stephanie Thomas, Magdalena Mair

Lyme disease, caused by bacteria in the Borrelia burgdorferi sensu lato group, is the most prevalent vector borne disease in the northern hemisphere, and the most prevalent tick borne disease in the whole world, with conservative estimates reporting 200 000 cases annually in Western Europe alone. In Europe, the disease is vectored mostly by the Ixodes ricinus tick, found throughout Europe. Whereas ticks have historically be found mostly in forested areas, they are nowadays also increasingly being found in urban green areas, raising concerns for human health. As urbanization continues globally, urban greening is being promoted for its many ecosystem services provided. However, the potential ecosystem disservices associated with urban greening, such as an increase in vector borne diseases, often get overlooked. This thesis examined if there is a difference in the prevalence of B. burgdorferi sensu lato. among I. ricinus ticks between urban, suburban and natural land cover classes across Europe, as well as if there is an effect of climate on said prevalence. To answer the research question, a systematic literature review was conducted, followed by a meta-analysis. Land cover classification was done using Google Earth satellite imagery, and the Köppen-Geiger climate classification was used for examining the effects of climate. The literature search identified previously obtained data on tick Borrelia prevalence from 18 papers, from 12 different European countries, in three different land cover classes and four climate classes. A significant interaction between land cover and climate class was found. However, the differences between the land cover classes within the climate classes were found to be nonsignificant in all cases. More research is needed into the potential effects of urbanization and urban greening on Borrelia prevalence, as well as more harmonized monitoring and reporting of Borrelia data in Europe.