Potential changes in the distribution of dengue transmission under climate warming

The purpose of the present paper is to document an initial attempt to quantify the influence of warming temperatures on the intensity and distribution of dengue transmission throughout the world using an expression of vectorial capacity modified to reflect the role of temperature on development and survival of the vector and virus. We rearranged the traditional vectorial capacity expression (the mean number of potentially infective contacts made by a mosquito population per infectious person per unit time) to develop an equation for the critical density threshold, an estimate of the number of adult female vectors required to just maintain the virus in a susceptible human population. In this expression, temperature influences adult survival, the lengths of the gonotrophic cycle and the extrinsic incubation period of the virus in the vector, and vector size, a factor that indirectly influences the biting rate. Before making projections for warming scenarios of current climate plus 2 or 4 degrees C, we validate our technique by successfully comparing model projections and the observed spatial, temporal, and altitudinal distribution of dengue using current climate in five cities that are endemic or have had epidemics in the past. Our results indicate that the current warming projection of the International Council of Scientific Unions and the Intergovernmental Panel on Climate Change of 2 degrees C by the end of the next century can be expected to result in a potential increase in the latitudinal and altitudinal range of dengue; the potential duration of the transmission season will also increase in temperate locations as well. We discuss how an increase in temperature-related transmission intensity can be expected to lower the average ages of primary and secondary infections and thereby significantly increase the proportion of secondary infections occurring among infants and adolescents, the ages especially susceptible to dengue hemorrhagic fever and shock syndrome.