A spatio-temporal modeling framework to assess the probability of human tick-borne encephalitis (TBE) infections across Europe

Background: Tick-borne encephalitis (TBE) is a viral disease of the central nervous system caused by the tick-borne encephalitis virus (TBEV). Despite the availability of a vaccine, TBE incidence is increasing with new foci of virus circulation. Within this context, modeling the occurrence of human TBE cases at the finest scale is essential to support targeted public health interventions. In response, this study presents a novel spatio-temporal modelling framework that provides annual predictions of human TBE presence in Europe. Methods: We used a boosted regression tree model trained on TBE data provided by the European Surveillance System (TESSy, ECDC) during the period 2017-2022. To account for the natural hazard of viral circulation, we included variables related to temperature, precipitation, land cover, and tick host presence. We also used proxies for human outdoor activity in forests and population density to account for human exposure to tick bites. Results:Our results highlight a statistically significant rising trend in the probability of human TBEV infections in north-western and south-western Europe. Such areas are characterised by the presence of key tick host species, forested areas, intense human recreational activity in forests, steep drops in late summer temperatures and high precipitation amounts during the driest months. The model showed good predictive performance, with a mean AUC of 0.85 at the regional level, and a mean AUC of 0.82 at the municipal level. Discussion: With ongoing climate changes, the burden of human TBEV infections on European public health is likely to increase. Hence, the development of a modeling framework that estimates the probability of human TBEV infections at the finest scale represents a step forward towards comprehensive TBE risk estimation. Our model will aid in identifying areas suitable for targeted TBEV detection surveys and support public health authorities in planning surveillance and prevention efforts.