Animal viral diseases and global change: bluetongue and West Nile fever as paradigms

Jiménez-Clavero, Miguel Á

Global warming is the rise in average surface temperature of the earth observed in the last decades (+0.6 • C in the last half century; IPPC, 2007) . This observation applies also specifically to Europe (EEA, 2012) and North America (Karoly et al., 2003) , territories particularly concerned to WNV and BT virus (BTV) emergences, as it will be discussed later. The increase has accelerated in recent years and is expected to go faster, so that in the twenty-first century the average surface temperature of the earth is expected to rise in a range between +1.6 and +6 • C, depending on the different scenarios considered (IPPC, 2007) . Although still a contentious issue, most scientists now accept that human activity has contributed to the observed global warming (Oreskes, 2004) , mostly through emissions of greenhouse gases produced by industrial activity and consumption of fossil fuels for transport, energy production, etc. (IPPC, 2007) . The impact of global warming on the environment is the subject of numerous recent studies, based on predictive modeling scenarios depending on the level of emissions. It is not the purpose of this article to review these models, which are described extensively elsewhere (IPPC, 2001 (IPPC, , 2007 , but to highlight some future climate trends, mainly in Europe, the scenario for some recent unusual observations regarding arboviral diseases (Purse et al., 2008; Wilson and Mellor, 2009; Zientara et al., 2009; Calistri et al., 2010; MacLachlan and Guthrie, 2010; Sotelo et al., 2011a) . For this, I will rely on data from the European project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects; Christensen, 2005) . Table 2 summarizes the most marked trends for Europe in the next 100 years according to this study. In addition to an increase in mean annual air temperature, predicted to be between 1.4 and 4.5 • C, depending on the areas (the highest rise is expected to occur in the Iberian Peninsula), the study suggests there will be more droughts, more wildfires, heat waves will be more frequent, and all this will be particularly noticeable in southern Europe. Winters will become milder, and this will occur more rapidly in northern latitudes. As a result, frost will decrease, and minimum temperatures will rise. These circumstances favor living cycles of certain arthropod vectors, which in these conditions will be able to overwinter more easily in latitudes and areas beyond their current geographic ranges. Other remarkable trends include rising temperatures and unusually hot summers, but also greater interannual variability, particularly in central Europe, which will make adaptations more difficult. Waves of extreme temperatures (both cold and heat) will become more frequent. With regard to rainfall, the tendency is to increase in northern Europe and decrease in the South. Therefore, increasingly severe droughts are expected in southern Europe, with a considerable impact on agriculture and water resources. However, torrential rains, especially in summer, will become more common throughout Europe, causing flooding to occur more frequently. Snow will become rarer. River flows will decrease in the South, and increase in northern Europe. Extreme wind events (hurricanes, cyclones) will also be more frequent.