An assessment of the distribution and spread of the tick Hyalomma marginatum in the western Palearctic under different climate scenarios.

We applied a process-driven model to evaluate the impact of climate scenarios for the years 2020, 2050, and 2080 on the life cycle of Hyalomma marginatum ticks in the western Palearctic. The net growth rate of the tick populations increased in every scenario tested compared to the current climate baseline. These results support the expectations of increased tick survival and increased population turnover in future climate scenarios. We included a basic evaluation of host movement based on rules connected to altitude, slope, size of the near patches, and inter-patch distances in the real landscape over the target area. Data on landscape were obtained from medium-resolution MODIS satellite imagery, which allowed us to test the potential spread of the populations. Such a model of host dispersal linked to the process-driven life cycle model demonstrated that eastern (Turkey, Russia, and Balkans) populations of H. marginatum currently are well separated and have little mixing with western (Italy, Spain, and northern Africa) populations. The northern limit is marked by the cold areas in the Balkans, Alps, and Pyrenees. Under the warmer conditions predicted by the climate scenarios, the exchange of ticks throughout new areas, previously free of the vector, is expected to increase, mainly in the Balkans and southern Russia, over the limit of the mountain ranges. Therefore, the northern limit of the tick range would increase. Additional studies are necessary to understand the implications of host changes in range and abundance for H. marginatum and Crimean-Congo hemorrhagic fever virus.