Uusitalo et al.
Modelling habitat suitability for occurrence of human tick-borne encephalitis (TBE) cases in Finland
Ticks Tick Borne Dis. 2020, in press, doi.org/10.1016/j.ttbdis.2020.101457
Finland lies in the zone, where the tick species, Ixodes ricinus and I. persulcatus overlap and where both TBE virus subtypes, the European and the Siberian, are transmitted by ticks. The geographical distribution of TBE cases is currently mainly focused in the coastal and Southern Finland including the Åland Islands. In the past years, the distribution of TBE cases has expanded to Central, Eastern, and Northern Finland, excluding northernmost Finland. The annual number of TBE cases has almost quadrupled in 11 years from 2007 (n=20) to 2017 (n=72), and a total of 488 cases has been reported in this time span.
Environmental, bioclimatic variables, ecological, habitat suitability models, and anthropogenic data were analyzed to build up a TBE risk map for the future. The authors concluded from the data that the distribution of TBE is affected by precipitation in April and July, snow-covered land in November, ecological factors such as the white-tailed deer, European hare, raccoon dog density and human population density. In the authors´ forecast, the mean temperature of the warmest month and wettest quarter and temperature seasonality were the most bioclimatic factors for TBE distribution.
Compared to current climate conditions, there is a slightly wider geographical extent of TBE virus transmission risk to Northern Finland and a high risk for Southern Finland, while no increase in TBE risk is predicted for Central and Eastern Finland.