Global patterns of aegyptism without arbovirus

The world’s most important mosquito vector of viruses, Aedes aegypti, is found around the world in tropical, subtropical and even some temperate locations. While climate change may limit populations of Ae. aegypti in some regions, increasing temperatures will likely expand its territory thus increasing risk of human exposure to arboviruses in places like Europe, Northern Australia and North America, among many others. Most studies of Ae. aegypti biology and virus transmission focus on locations with high endemicity or severe outbreaks of human amplified urban arboviruses, such as dengue, Zika, and chikungunya viruses, but rarely on areas at the margins of endemicity. The objective in this study is to explore previously published global patterns in the environmental suitability for Ae. aegypti and dengue virus to reveal deviations in the probability of the vector and human disease occurring. We developed a map showing one end of the gradient being higher suitability of Ae. aegypti with low suitability of dengue and the other end of the spectrum being equal and higher environmental suitability for both Ae. aegypti and dengue. The regions of the world with Ae. aegypti environmental suitability and no endemic dengue transmission exhibits a phenomenon we term ‘aegyptism without arbovirus’. We then tested what environmental and socioeconomic variables influence this deviation map revealing a significant association with human population density, suggesting that locations with lower human population density were more likely to have a higher probability of aegyptism without arbovirus. Characterizing regions of the world with established populations of Ae. aegypti but little to no autochthonous transmission of human-amplified arboviruses is an important step in understanding and achieving aegyptism without arbovirus.Author summary: The preeminent vector of arboviruses, Aedes aegypti, is distributed globally and capable of transmitting deadly pathogens to over half the world’s population. While most studies focus on areas where Ae. aegypti and human-amplified urban arboviruses such as dengue and Zika viruses are locally established, our study explores the margins of endemicity where Aedes aegypti can be found, but arboviral illness is rare. These areas where we find environmental suitability for the vector but an absence of established arboviral transmission we term ‘aegyptism without arbovirus’. This builds on the long-held observation of ‘anophelism without malaria’ in which some regions having Plasmodium-competent Anopheles spp. mosquitoes but not the associated human malaria. This study uses previously published maps to reveal locations with higher suitability of Ae. aegypti and low suitability of dengue. Additionally, we analyzed the resulting map of deviations between Ae. aegypti and dengue and found significant associations with human population density, Infant Mortality Rate, temperature, and precipitation. To the best of our knowledge, this is the first study to characterize places around the world that exhibit ‘aegyptism without arbovirus’ which is an important first step in our ongoing battle with human-amplified urban arboviruses.