Increased Relative Risk of Tick-Borne Encephalitis in Warmer Weather

Area of Science:

• Epidemiology
• Vector-borne diseases
• Environmental health

Background:

• Tick-borne encephalitis (TBE) is a significant neuroinfection transmitted by *Ixodes ricinus* ticks.
• TBE incidence is seasonal, correlating with tick activity, but the exact drivers of risk variation require further understanding.

Purpose of the Study:

• To investigate the relationship between questing tick activity and TBE case incidence.
• To identify factors influencing the discrepancy between peak tick activity and peak TBE risk.
• To develop improved TBE risk prediction models.

Main Methods:

• Comparison of TBE case data (2001-2006) with weekly monitoring of *I. ricinus* nymphal activity.
• Analysis of temporal correlations, including a 21-day time shift, between tick abundance and disease onset.
• Evaluation of meteorological data and its impact on TBE incidence and tick activity.

Main Results:

• TBE cases and questing nymph counts exhibited similar bimodal annual distributions.
• The ratio of TBE cases to nymphs was highest in summer-autumn, despite peak nymphal activity in spring-summer.
• Extreme weather events altered TBE incidence patterns, suggesting climate influence.
• Higher temperatures in summer-autumn likely increase virus replication in ticks, elevating TBE transmission risk.

Conclusions:

• Temperature significantly influences TBE risk by affecting virus replication within the tick vector.
• The discrepancy between peak tick activity and peak TBE risk is explained by temperature-dependent viral replication.
• Weather-based forecasts, incorporating ambient and average temperatures, can enhance real-time TBE risk prediction.