Targeted monitoring informed by mapping the ongoing spread of tick-borne encephalitis virus, the Netherlands

BACKGROUND Tick-borne encephalitis virus (TBEV) was detected in the Netherlands in 2015. Current monitoring through serology in deer, tick collection and reported human cases, may underestimate areas of virus circulation. Including estimates of suitability of the habitat for TBEV can guide risk-based monitoring. AIM We aimed to improve the accuracy of the TBEV distribution map by adding estimates of TBEV habitat suitability to guide targeted tick monitoring in newly identified risk regions. METHODS Habitat suitability for TBEV was assessed by calculating the basic reproduction number (R 0 ) for 1 km 2 grid cells aggregating various data sources for tick hosts such as mice or voles, tick abundance and TBEV transmission. The importance of different tick hosts was determined in scenario analyses. The baseline scenario was validated against data on seropositive roe deer and TBEV-positive ticks and rodents. RESULTS The suitability (R 0 ≥ 1) was associated with tick habitat suitability and the abundance of competent host species. Variation in competent host densities had a greater effect on R 0 estimates than incompetent hosts. Monitoring data corresponded well with model-predicted high-risk areas and confirmed further spread of TBEV. CONCLUSION The TBEV suitability map is a useful tool for targeted sentinel surveillance by identifying new risk areas, informing local municipal health services of endemic areas for potential human exposure. Our results support targeted efforts for awareness, preparedness and outbreak response, even in regions where TBEV has not yet been detected. Integrating One Health monitoring with spatial modelling can strengthen preparedness in emerging TBEV regions.