EO in Epidemio

Tick borne Encephalitis

Tick borne Encephalitis

Fact sheet

Ticks are currently considered to be second only to mosquitoes as vectors of human infectious diseases in the world. (Source: WHO 2014)
Approximately 10000–12000 clinical cases of tick-borne encephalitis are reported each year, but this figure is believed to be significantly lower than the actual total. Most infections with the virus result from tick bites acquired during outdoor activities in forested areas. (Source: WHO 2014)
As the incidence of tick-borne illnesses increases, the geographic areas in which they are found expand, and in some cases there is no possibility to help and recover infected humans completely. Therefore it becomes increasingly important to develop warning systems, map risk areas and install approached to reduce infection risks.

Number of confirmed TBE cases, EU/EEA 2014 based on national country reports. (Source: European Center for Desease prevention and control. Annual epidemiological report 2015. TBE. Stockholm: ECDC; 2016).

Ticks tend to be more active during warmer months, though this varies by geographic region and climate. Areas with woods, bushes, high grass, or leaf litter are likely to have more ticks.
Ground temperature and humidity over time are also of great importance for the live cycle of ticks.
As environmental data can be obtained from satellites it is possible to evaluate relevant parameters of vector distribution by analysing satellite data and correlating satellite derived information with ground measurements. The main benefit will be an increasing spatial and increasing temporal availability of relevant satellite data.

Map examples

With satellite information it might be possible to provide regular updated maps of tick infested areas with potential risks for tick transmitted diseases. The main benefit will be an increasing spatial coverage of environmental predictors for infection risks. Time series will also increase the temporal resolution of future risk mapping updates. During user meetings the following Earth Observation variables were identified for the service development for TBE:

Habitat structure and distribution information such as land use / land cover maps and forest density information will be used for extracting specific habitats that represent best conditions tick occurrences, a key indicator for impacts with TBE pathogens. Habitat structure and distribution provides valuable information on the connectivity of pathogen clusters and human interaction intensities within different habitats.

Land Use / Land Cover: Maps about the current status of specific Land Use Land Cover (LULC) classes and habitat types are required to correlate hot spots of habitat characteristics of ticks and infection hot spots with patterns of potential human interaction.

Tree Cover Density: Current maps describing the vegetation structure add further information on the habitat delimitation of ticks. The tree cover density dataset maps the level of tree cover density in a range from 0-100%.

LULC maps will be used to derive tick habitats resp. land cover types that ticks prefer. The figure below shows a first local scale LULC test mapping for the TBE test site Berlin, derived from Landsat-8 satellite images from 2015.

LULC (local scale):

LULC map 2015 Berlin, Germany

LULC (National scale):

Land Cover for Germany based on the ESA CCI Land Cover Product. Further details on the nomenclature are provided in the legend description.

Tree cover density for Germany based on the Copernicus High Resolution Layer of Forests.

 

Land Surface Temperature:

Land Surface Temperature: Surface temperature is one of the most probable indicators for the prevalence and in particular activity of ticks, the vector of TBE. LST data are used for the extraction of activity layers and tick activity alert maps for tick activity for the reference years 2000 -2016 based on temperature thresholds using MODIS time series.

Ticks become active just if a certain temperature was reached for several days. LST time series will be used for mapping the seasonality and inter-annual changes from 2000 to 2016 and the seasonality in selected years using MODIS time series. Comparisons of climate station data with satellite-based LST data will be used to evaluate LST data for the tick activity estimation. The example shows the 15 year average land surface temperature for the month of April. The red coloured regions show the areas with an increased probability for tick activity. Daily LST observations are used to map the spatial and temporal activity pattern of ticks.

Inter-annual mean land surface temperature productderrived from MODIS daytime and nighttime observations.

Results

 

Tick occurrence risk mapping

The resulting tick occurrence risk map provides an overview of the main distribution of probable tick occurrence in Germany within a three-class classification system. According to the geo-factors land cover, tree density and elevation the main ecological regions with preferred habitat conditions for increased tick occurrences. The three classes were selected in order to have a fast and efficient understanding of the main risk areas. This means that the high risk class covers in particular the forested areas including open woodlands and grasslands. This is visible for the high and low mountain ranges, e.g. Thuringian Forest and Harz Mountains, but also und the Alpine regions in southern Germany as well as the Schwarzwald Mountain ranges and the Pine forests in Western Pommerania.

The medium risk areas are mainly distributed within the large scale agricultural areas of Germany including low vegetation cover areas. The low risk areas are dominated by high urban densitiy areas, non-vegetated areas and water bodies.

Tick occurrence risk map for Germany.

Tick activity risk mapping

The tick activity risk maps were derived on a monthly basis to provide a general image of the spatial distribution of periods with tick activity by applying the temperature threshold for tick activity on inter-annually and monthly aggregated LST time series. The monthly tick activity maps aim at providing the general temporal patterns of probable tick movement on a monthly basis in Germany. The general tick activity maps provide the basis for a further implementation of a tick activity alerting by using satellite-based LST observations.

The maps show no tick activity for in the winter months from November to December. The zones of early spring tick activity starts in the Lowe Rhine valley according to the south-east temperature gradient in Germany. From April onwards ticks are active in all lower elevations in Germany. The low mountain ranges show in average no tick activity in April. The summer months are characterized with tick activity in all districts in Germany since temperatures lower than 8°C are not observed in the inter-annual mean. For the fall season the tick activity declines in the eastern part of Germany. The south-western and western parts of Germany show increases average temperatures. In particular the high density urban areas are in average over the 8 °C threshold and mapped as areas with probable tick activity.

Inter-annual monthly tick activity maps (LST threshold of 8°C). The maps indicate the monthly tick activity patterns based on MODIS LST observations and geo-spatial modeling techniques.

Interactive Map for tick risk in Germany

Detailed explorations of the tick occurrence risk and activity can be done within the interactive web map

Link to the Web Map: WebGIS