Kommer antal anmälda TBE-fall att öka om årstiderna blir varmare?

Abstract

Background Studies have shown that the global temperature is increasing due to emission of greenhouse gases. Europe is the continent where the temperature is increasing the most. The ticks’ survival and reproduction benefits from a warmer climate. Due to increased global temperature, there is a risk that tick-borne diseases like TBE will continue to increase. Research question Is there any relation between reported TBE-cases and warmer temperatures during winter, spring, summer and autumn in Västra Götaland? Materials and methods Temperatures during each season that are fundamental for Ixodes ricinus and the TBE-virus were used to construct temperature intervals for the different seasons. Nine municipalities in region Västra Götaland were included in the study, based on having a weather station in the municipality or nearby where temperature data could be obtained, and having at least 20 cases of TBE between 2005 and 2024 assumed to result from tick exposure in the municipality. The average number of days that the temperature lay within each interval was calculated for the nine municipalities. Number of TBE cases were then compared with the number of days for each temperature intervals for the year the case was reported and the year before with Spearman’s rank correlation. Results A significant increase in reported TBE-cases was seen when there was a previous winter with days with temperatures between 0 °C and below 5 °C (Spearman’s rho: 0,55; p=0,013). Many days during a previous autumn with temperatures at least +10°C was related to increased reported TBE-cases the year after (Spearmans rho: 0,526; p=0,017). Fewer reported TBE-cases were seen when many days during the previous summer had a temperature below +10 °C (Spearman’s rho: -0,72; p=<0,001). Conclusion There is a correlation between temperatures during several seasons preceding reported TBE-cases. Since the global temperature is increasing there is a risk that the numbers of reported TBE-cases will continue to increase.