Abstract
The numbers of reported human tick-borne encephalitis (TBE) cases in Europe have increased in several endemic regions (including Finland) in recent decades, indicative of an increasing threat to public health. As such, it is important to identify the regions at risk and the most influential factors associated with TBE distributions, particularly in understudied regions. This study aimed to identify the risk areas of TBE transmission in two different datasets based on human TBE disease cases from 2007 to 2011 (n = 86) and 2012–2017 (n = 244). We also examined which factors best explain the presence of human TBE cases. We used ensemble modelling to determine the relationship of TBE occurrence with environmental, ecological, and anthropogenic factors in Finland. Geospatial data including these variables were acquired from several open data sources and satellite and aerial imagery and, were processed in GIS software. Biomod2, an ensemble platform designed for species distribution modelling, was used to generate ensemble models in R. The proportion of built-up areas, field, forest, and snow-covered land in November, people working in the primary sector, human population density, mean precipitation in April and July, and densities of European hares, white-tailed deer, and raccoon dogs best estimated distribution of human TBE disease cases in the two datasets. Random forest and generalized boosted regression models performed with a very good to excellent predictive power (ROC = 0.89–0.96) in both time periods. Based on the predictive maps, high-risk areas for TBE transmission were located in the coastal regions in Southern and Western Finland (including the Åland Islands), several municipalities in Central and Eastern Finland, and coastal municipalities in Southern Lapland. To explore potential changes in TBE distributions in future climate, we used bioclimatic factors with current and future climate forecast data to reveal possible future hotspot areas. Based on the future forecasts, a slightly wider geographical extent of TBE risk was introduced in the Åland Islands and Southern, Western and Northern Finland, even though the risk itself was not increased. Our results are the first steps towards TBE-risk area mapping in current and future climate in Finland.
Highlights
High-latitude regions (> 60°) in the Northern Hemisphere are undergoing rapid changes associated with climate warming
Our study suggests that the distribution of tick-borne encephalitis (TBE) is affected by environmental factors such as mean precipitation in April and July, proportion of snow-covered land in November, forest, and field; ecological factors such as white-tailed deer, European hare, and raccoon dog density; and anthropogenic factors including proportion of built-up areas, human population density, and people working in the primary sector
Our results confirm the influence of game animal densities and anthropogenic and environmental factors on distribution of human TBE disease cases in Finland
Summary
High-latitude regions (> 60°) in the Northern Hemisphere are undergoing rapid changes associated with climate warming. As a result of these climatic changes, distribution of invasive species is expanding to new regions and environmental conditions have become more suitable for the circulation of several vectorborne viruses (Koch et al, 2017; Hobbs, 2000; Jore et al, 2014; Sutherst et al, 2000). Ensemble modelling and geographical information systems (GIS) have been used to understand the connections between vectors, their habitats, and vector-borne diseases (Honig et al, 2019; Stefanoff et al, 2018; Gama et al, 2017; Sun et al, 2017; Deka and Morshed, 2018). GIS and ensemble modelling approaches used for identification of influential environmental factors and estimation of vector-borne disease risks can improve knowledge on disease prevention
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