Mapping the risk of tick-borne encephalitis in Europe for informed vaccination decisions

Abstract

Tick-borne encephalitis is increasing across Europe, yet public awareness lags. Geo-visualizations leveraging openly available data empower travellers and health authorities in making informed (vaccination) choices. We urge improved surveillance and synchronization of data for easily accessible and understandable (geo) health information, to enhance early detection of infections.

The tick-borne encephalitis virus (TBEV), a virus of the Flaviviridae family that can affect the central nervous system of humans, is on the rise in many parts of Europe.¹ A vaccine that is 95% effective is available, yet one seldom thinks about needing to get vaccinated when visiting or travelling within Europe. We utilized openly available data to investigate if travel advices on the topic of tick-borne encephalitis (TBE) could benefit members of the general public so that they can make informed decisions about vaccinations, particularly if planning a visit to rural areas and the outdoors where they may come into contact with ticks or unpasteurized dairy products.

TBE is the second most common tick-transmitted disease in Europe and one of the most widespread tick-borne diseases in the Euro-Asia region.¹ TBE is endemic in 27 European countries,¹ spreading from Alsace-Lorraine (France) to Vladivostok (Russia), China, Japan and South Korea in the east, and from Scandinavia to Italy and Greece in the south.¹

Each year 12 000 human TBE cases are reported globally with 3500 cases reported annually in Europe² (Supplementary File 1). These numbers are likely an underestimate.¹ In Europe, TBE cases are irregularly distributed (Supplementary Files 1–3) as is shown in the TBEV risk map we created based on notification rates (Figure 1). Clear differences between countries can be seen with increased risks seen in Switzerland, Austria, Czechia, Northern Italy, Southern Germany, Estonia, Latvia, Lithuania, Poland, Slovakia, Slovenia and parts of Sweden.

Figure 1.

Map of TBEV public health risk based on notification rates (data sources^1–3). For Norway and Italy, TBE data were obtained from Chapter 14.¹ The map was created using Bayesian Kriging interpolation method in ArcGIS Pro.

The public health impact of a vector-borne infection such as TBE is partly dependent on travel movements of the population. After all, higher numbers of people visiting a high-endemic region amplifies the absolute number of infections.

During 2022, 39.4% of EU residents visited TBE risk areas (see Supplementary File 2 for case by country). The top five overnight trips of residents of Western European countries (Belgium, Germany, Ireland, France, Luxembourg, Netherlands and Austria) were to countries with TBE risk (e.g. Italy (NR = 0.01–90.4), Germany (NR = 0.1–9.7), Austria (NR = 0.1–3.6) and Croatia (NR = 3.61–6.78)). In the Netherlands, 57% of all TBE cases were acquired in Austria, Germany and Sweden.¹ Similarly in Spain, all cases were imported from Estonia and Austria⁴, and in Belgium, infections were acquired in Estonia, Germany, Austria, Scandinavia, Slovenia and Czechia.¹

Among the most effective mitigation measures against TBE are measures to avoid tick bytes altogether, such as wearing (impregnated) long trousers and sleeves, using tick repellents and inspecting the body for ticks after outdoor activities (and immediately removing them when needed). Yet, vaccinations to date remain the most effective measure to prevent TBE with 2 doses and 95% effectiveness with irregular vaccinations, reaching 99% effectiveness in populations regularly vaccinated.⁵ Although vaccinations are part of the national vaccination plan of Austria⁶ and Czechia, they are not commonly applied throughout Europe, with highly varying recommendations⁷ and vaccine uptake across Europe.⁸

In the vast majority of European countries, where vaccinations are not a standard measure, it is up to the individual to pro-actively seek health advice and determine whether a vaccination is called for, when travelling. The same goes for deciding to apply mitigation measures. To enable such efforts by the public, centralized, easily accessible and understandable information is needed, but is not always available.

Future work and recommendations

To allow for the public health domain to optimally benefit from available data, it is widely acknowledged that surveillance must be improved across countries (see Notifiable Disease Reporting for Europe in⁹) and that it must be ensured that data are easily accessible and structured in a way that allows for these data to be integrated into public health communications more efficiently. Ideally, such surveillance data should not be limited to human clinical cases but should also incorporate data on other reservoirs (e.g. wildlife, vectors, livestock, environment) to allow for early detection and the prediction of upsurges in infection rates.

Having such integrated data available will allow for travellers to determine if and what vaccines are needed (e.g.¹⁰) and for public health authorities to make better risk assessments and plan their (recommended) travel measures accordingly.^9,10 Insights gained from analyzing these data spatially, as demonstrated here (Figure 1) can be instrumental in communicating such health information to the public in an understandable and easily accessible manner. Key preconditions for this are that the outputs of the analyses are easily understood, and fit the users’ needs and use context. This involves, for example, design, but also data input and retrieval of the data. It is therefore crucial to involve stakeholders throughout the development and implementation of geo-visualizations and informational dashboards.

Finally, when looking beyond the borders of TBE, we are convinced that this combination of measures would benefit public health in more ways than one. Having improved surveillance, synchronized data, and easily accessible and understandable health information available can make an important contribution to early detection of new infections as well as upsurges of (re-)emerging infections across Europe and the globe.

Data

All data used for this analysis are available in the public domain. TBE data were available for various years and at a variety of geographic scales from.^1–3 The NUTS (nomenclature of territorial units for statistics) boundaries were obtained for scale 01 M and 20 M from Eurostat https://ec.europa.eu/eurostat/web/gisco/geodata/statistical-units/territorial-units-statistics. Country boundaries were obtained from GADM https://gadm.org/. All maps and spatial analyses were conducted in ArcGIS Pro v2.8.3.

Author contributions

N.B.J. and J.B. were involved in conceptualization, writing and editing of the manuscript. J.B. created the visualizations used in the manuscript.

Nienke Beerlage-de Jong (Conceptualization [equal], Writing—original draft [equal], Writing—review & editing [equal]) and Justine Blanford (Conceptualization [equal], Visualization [lead], Writing—original draft [equal], Writing—review & editing [equal]).

Funding

This work was supported by the University of Twente Climate Centre.

 

Conflict of interest: None declared.