Towards New Horizons: Climate Trends in Europe Increase the Environmental Suitability for Permanent Populations of Hyalomma marginatum (Ixodidae)

Abstract

Ticks and tick-borne pathogens are changing their current distribution, presumably due to the impact of the climate trends. On a large scale, these trends are changing the environmental suitability of Hyalomma marginatum, the main vector of several pathogens affecting human health. We generated annual models of environmental suitability for the tick in the period 1970-2018, using harmonic regression-derived data of the daily maximum and minimum temperature, soil moisture and water vapor deficit. The results demonstrate an expansion of the suitable area in Mediterranean countries, southeast central Europe and south of the Balkans. Also, the models allowed us to interpret the impact of the ecological variables on these changes. We deduced that (i) maximum temperature was significant for all of the biogeographical categories, (ii) soil humidity has an influence in the Mediterranean climate areas, and (iii) the minimum temperature and deficit water vapor did not influence the environmental suitability of the species. The conclusions clearly show that climate change could create new areas in Europe with suitable climates for H. marginatum, while keeping its "historical" distribution in the Mediterranean. Therefore, it is necessary to further explore possible risk areas for H. marginatum and its associated pathogens.

Keywords: Europe; Hyalomma marginatum; climate trends; environmental suitability.

Figure 1

Spatial changes of environmental suitability for Hyalomma marginatum in five time slices covering periods of 10 consecutive years. (a) 1970–1979, (b) 1980–1989, (c) 1990–1999, (d) 2000–2009, (e) 2010–2018.

Figure 1

Spatial changes of environmental suitability for Hyalomma marginatum in five time slices covering periods of 10 consecutive years. (a) 1970–1979, (b) 1980–1989, (c) 1990–1999, (d) 2000–2009, (e) 2010–2018.

Figure 2

The slope of the changes of environmental suitability for Hyalomma marginatum in the target territory in the period 1970–2018. A positive slope is not correlated with a suitable environmental for the tick (see Figure 1 for this data), but rather, only the strength of changes of the environmental variables in the period of reference. These changes are shown in (b) with explicit reference to the biogeographic divisions in (a).

Figure 3

Environmental variables with statistical significance in the changes of environmental suitability for Hyalomma marginatum in the period 1970–2018, obtained from a multiple regression among the slope of changes of suitability (dependent variable) and several environmental variables (explanatory variables). The results were calculated separately for each of various selected biogeographic areas, which cover more than 80% of the territory. Two heat maps are associated with the tables in which the “p” values for each variable are included: cells in red represent highly significant variables. The abbreviations of the variables are: SoilQ10, SoilQ90, and Soil (percentiles 10 and 90 of the soil moisture and the total annual soil moisture, respectively); VPDTotal (sum of the annual values of daily water vapor deficit), VPDQ10 and VPDQ90 (percentiles 10 and 90 of the of the daily water vapor deficit) in figure (a); and TMAX_10 (annual sum of the daily maximum temperature values exceeding of 10 °C), TMAX_Q10 and TMAX_Q90 (percentiles 10 and 90 of the of the daily maximum temperature values), TMAX_d10 (number of days in a year in which maximum temperature exceeded 10 °C); TMIN_10 (annual sum of the daily minimum temperature values exceeding of 10 °C), TMIN_Q10 and TMIN_Q90 (percentiles 10 and 90 of the of the daily minimum temperature values), TMIN_d10 (number of days in a year in which minimum temperature exceeded 10 °C) in figure (b).

Figure 4

Changes in the sum of daily annual maximum temperature and of solid moisture for selected biogeographical regions. The X axis represents the sum of maximum temperature in degrees Celsius; the Y axis indicates the sum of soil relative humidity in kPa.