Masterarbeit

Can Climate and Land Cover Explain the Absence of Tick-Borne Encephalitis Virus in Some Parts of Eurasia?

Maike Stumpf (04/2020-09/2020)

Betreuer: Stephanie Thomas

Aim Tick-borne encephalitis is a wide-spread disease in Eurasia transmitted by various tick species. Not much is known about the virus causing it, especially the mechanisms behind its distribution mainly in central and eastern Eurasia, and its absence in western Europe and southern and northern Eurasia. The hypothesis in this study is that the absence of TBEV in these parts of Eurasia can be explained with climate and land cover, and that climate is the more important driver of the absence of TBEV. Methods In a detailed literature review the TBEV endemic regions of all Eurasian States were gathered. With that, a detailed and up to date presence and absence map of TBEV was created. 19 bioclimatic variables and land cover information were used as environmental data. Using Maxent two species distribution models were built, determining the ecological niche of the virus and the variables most important for its presence in some parts, and its absence in others. Results In both models, the variable ‘Annual Mean Temperature’ was the most important environmental factor explaining the presence and the absence of TBEV. An ‘Annual Mean Temperature’ around 2.5 °C is most favorable for the presence of TBEV, and -11 °C as well as 18 °C for its absence. Land cover did only have a minor influence on the presence of TBEV with ‘Closed to open mixed broadleaved and needleleaved forest’ being the land cover class with the highest probability of occurrence of TBEV. For TBEV absence, land cover plays a slightly bigger role, with ‘Closed to open broadleaved evergreen or semi-deciduous forest’ being the land cover class with highest probability of absence of TBEV. Main Conclusions The results suggest that climate is more important than land cover for the distribution of TBEV in Eurasia on a broad scale, and that both climate and land cover can explain the absence of TBEV in some parts of Eurasia.