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

Jiménez-Clavero, Miguel Á

How will these climate changes impact on emerging infectious diseases? The consequences of global warming are expected to be diverse and highly variable in different geographical locations. For example, as noted above, the effects of climate change in Europe will differ significantly between northern and southern latitudes, and these differences could even be greater at the local level, although they will not be easily distinguished from weather variations. These changes may affect disease emergence not only through direct effects on populations of vectors, reservoirs, and hosts, but also indirectly, through, for instance, induced changes in human activities. For instance, in a scenario like that depicted in the predictive climatic models above cited for southern Europe, lower rainfall, increased temperature, and reduced water availability will have important consequences not only on agricultural activities which, as already noted, have a major impact on infectious diseases, but for example on tourism, which is the main source of wealth in these regions. A significant decline in economic activity could lead to a decrease in population, food demand, and hence livestock. In this changing context, plenty of uncertainties, it is difficult to predict an overall trend: some infectious diseases will probably emerge, some existing ones will spread, and others may disappear. Even in specific cases a disease may be exacerbated transiently and disappear later. For example, the cease of agricultural production in irrigation areas, which can likely occur in a scenario of extreme drought, could lead at long-term to local extinction of mosquito-borne diseases, whose breeding habitat depends on the infrastructure dedicated to this type of agriculture. However, disuse and neglect could favor the accumulation of organic matter in certain points of these infrastructures, turning them into optimal habitats for breeding of vectors, something that the normal maintenance of the network usually avoids. This would likely lead to a transient increase in the incidence of certain diseases, although prolonged drought would eventually lead these vectors to extinction.