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 di stribution of dengue transmission throughout the world using an expres sion of vectorial capacity modified to reflect the role of temperature on development and survival of the vector and virus. We rearranged th e traditional vectorial capacity expression (the mean number of potent ially 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 b iting rate. Before making projections for warming scenarios of current climate plus 2 or 4 degrees C, we validate our technique by successfu lly comparing model projections and the observed spatial, temporal, an d altitudinal distribution of dengue using current climate in five cit ies that are endemic or have had epidemics in the past. Our results in dicate that the current warming projection of the International Counci l of Scientific Unions and the Intergovernmental Panel on Climate Chan ge of 2 degrees C by the end of the next century can be expected to re sult 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 i n temperature-related transmission intensity can be expected to lower the average ages of primary and secondary infections and thereby signi ficantly increase the proportion of secondary infections occurring amo ng infants and adolescents, the ages especially susceptible to dengue hemorrhagic fever and shock syndrome.