Linking Environmental Drivers to Infectious Diseases: The European Environment and Epidemiology Network

Europe is increasingly at risk of the emergence of tropical diseases that are more commonly associated with warmer climates [1]. In 2010, Southeastern Europe witnessed an upsurge in West Nile fever cases that was strongly associated with excessive heat waves that had occurred in the preceding weeks [2]. France sustained its first autochthonous dengue transmission in the summer of 2010, and Madeira is currently experiencing the first persistent dengue transmission in Europe since 1920 [3]. In addition, the first outbreak of chikungunya outside the tropics occurred in 2007 in Italy, with subsequent autochthonous cases in France and Croatia in 2010 [4], and since 2009, Greece has experienced a resurgence of indigenous cases of Plasmodium vivax transmission in environmentally and climatically suitable areas [5]. Globalization and environmental change, social and demographic factors, and health system capacities are all significant drivers of infectious diseases [6]. International travel and trade can facilitate the dispersal of vectors and pathogens to new areas that are increasingly climatically and environmentally suitable. Environmental factors, such as agriculture, irrigation, and deforestation, are other important determinants of emerging infectious diseases. Urbanization and urban sprawl have encroached upon agricultural and seminatural areas in Europe, and the trend is expected to continue in many places. One consequence of habitat destruction is the displacement of wildlife, sometimes into urban or abandoned environments, which can in turn affect human exposures to infectious pathogens. In addition to the above, climate significantly influences the transmission of infectious diseases. Many zoonotic enteric pathogens, including salmonella, cryptosporidium, VTEC, and campylobacter, are known to exhibit seasonal patterns, while climatic conditions including temperature and rainfall influence the transmission of vector-borne diseases ranging from tick-borne encephalitis to dengue [7], [8]. Thus anthropogenic climate change, which has accelerated over the past decade, may lead to shifts in the distribution of infectious diseases [9]. Environmental drivers are often epidemic precursors of disease, meaning that monitoring changes in environmental conditions can guide the anticipation and forecasting of upsurges in infectious disease [10]. At an ecological level, the utility of predictive models has been documented for a number of case studies. For example: deer mice density has been used to predict hantavirus infections [11]; rainfall and temperature have been used as predictors of high-risk areas of plague and hantavirus pulmonary syndrome [12]; sea surface temperature, elevated rainfall, and vegetation index have been used to predict outbreaks of Rift Valley fever [13]; expansion of schistosomiasis in China has been linked to climate change scenarios [14]; climate change models have been used to predict Lyme disease risk and to forecast the emergence of tick-borne infectious disease [15]; and shifts in patterns of transmission of plague and tularemia have been assessed in relation to climate change [16]. A common message from these diverse studies is that merging environmental, remotely sensed, demographic, epidemiological, and other relevant data sets on the basis of common spatiotemporal features allows for the integrated analysis of complex interactions. In turn, identifying long-term trends will build the evidence base for strategic public health action, while identifying short-term events linked to environmental conditions can help improve and accelerate early warning and response capabilities. The European Centre for Disease Prevention and Control (ECDC) has recognised the strategic importance of such capabilities and has developed an information infrastructure coined the European Environment and Epidemiology (E3) Network, aimed at monitoring environmental conditions related to infectious disease threats [17]. The E3 Geoportal (http://E3geoportal.ecdc.europa.eu/), to be launched in 2013, will support data exchanges and sustained collaborations between EU Member States, researchers, and other interested collaborators (Figure 1). The E3 Network has been specifically designed with the intent of promoting European-wide research into environmental infectious disease epidemiology, leveraging existing European Community investments in this field, and facilitating the exchange of relevant data sets. In addition, the E3 Network also aims to provide technical support for the reporting, monitoring, analysis, and mapping of data and to enhance the analytical capacity of existing resources in Europe. Results could then be disseminated to policy makers, public health practitioners, European Union and international agencies, other governmental sectors, and nongovernmental organisations. Figure 1 Strategic focus of the E3 Network. For example, data from the E3 Network have recently been used to delineate areas suitable for malaria transmission in Greece during the resurgence of locally acquired Plamosdium vivax [5]. The objective was to define the environmental profile of areas with active transmission cycles between 2009 and 2012 and, based on this, to demarcate other regions at risk for malaria reemergence in Greece. A prediction model was developed with a number of environmental variables, including temperature (day- and nighttime Land Surface Temperature (LST)), vegetation seasonal variations (Normalized Difference Vegetation Index (NDVI)), altitude, land cover categories, and demographic indicators. These variables predicted suitability of areas for persistent malaria transmission characterized by low elevation, elevated temperatures, and intensive, year round irrigated agriculture with complex cultivation patterns (Figure 2). Such spatial analyses can help guide public health preparedness and response to infectious disease threats by directing surveillance and vector control activities. Figure 2 Areas predicted to be environmentally suitable for persistent malaria transmission in Greece, 2013.