High habitat richness limits the risk of tick-borne encephalitis in Europe: a multi-scale study

The natural transmission cycle of tick-borne encephalitis (TBE) virus is enhanced by complex interactions between ticks and key hosts strongly connected to habitat characteristics. The diversity of wildlife host species and their relative abundance is known to affect transmission of tick-borne diseases (such as, for example, Lyme disease). In the current context of global biodiversity loss, we explored the relationship between the habitat richness index (HRI) and the pattern of human TBE cases in Europe to assess the role of HRI in disease risk mitigation. Methods: We assessed human TBE case distribution across 879 European regions using official epidemiological data reported to the European Surveillance System (TESSy) between 2017 and 2021 from 15 countries. We statistically explored the relationship between TBE presence and a novel variable - the habitat richness index (HRI) - describing the diversity of European ecosystem types. We also validated our findings at local scale using data collected between 2017 and 2021 in 227 municipalities located in Trento and Belluno provinces, two known TBE foci in northern Italy. Findings: Our results showed a significant parabolic effect of HRI on the probability of presence of human TBE cases in the European regions included in our dataset, and a significant, negative effect of HRI on the local presence of TBE in northern Italy. At both spatial scales, TBE risk decreases in areas with higher values of HRI. Interpretation: To our knowledge, no efforts have yet been made to explore the relationship between habitat richness and TBE risk, both in local and in large scale geographical contexts, probably due to the scarcity of high-resolution, large-scale data about the abundance or density of critical host species, such as rodents and ungulates. To overcome this lack o f data, in this study we considered habitat richness as proxy of vertebrate host biodiversity to disentangle its role in driving TBE European occurrence at different spatial scales. The results suggest that biodiversity loss could considerably enhance disease risk for both humans and wildlife, which may influence biodiversity conservation policies within a One Health context approach.