A Reevaluation of the Role ofAedes albopictusin Dengue Transmission

Vector-borne pathogen transmission cycles are complex. Understanding the factors that drive the major events of transmission— introduction, emergence, persistence, and expansion—is a sought-after goal. Dengue is a major public health concern and is spreading rapidly through tropical, subtropical, and even (transiently) temperate areas [1].Estimates indicate that almost 100 million cases of dengue occur annually [2]. Pathogen introductions fail more often than they succeed. In 2014, for example, the Florida Department of Health Arbovirus Surveillance program reported 80 cases of dengue diagnosed in returned travelers. Despite this number, there were only 6 cases of local transmission, the timing of which suggests, at minimum, 3 small chains of transmission [3]. Additionally, there were almost 1000 cases of chikungunya virus infection diagnosed in returning travelers in the continental United States and only 11 cases of autochthonous transmission in Florida (again, likely involving several very small chains of transmission) [3]. So what confounds large-scale emergence of these pathogens? And once a pathogen has emerged, what will drive the level towhich it persists? Further still, what factors will lead to expansion, either spatially, as a pathogen moves to new areas, or temporally, as the transmission season lengthens? There are some obvious answers, including increased global travel, urbanization and habitat encroachment (for zoonoses), population susceptibility profiles, and availability of requisite vectors and climate change [1]. When assessed on a global scale, these factors may be enough to evaluate correlative relationships among variables and transmission outcomes and to predict large-scale transmission patterns, but with low precision or limited geospatial scale [4, 5]. However, understanding these transmission patterns may be more complex. Much attention has been given to the differences among and within dengue virus (DENV) serotypes with respect to vector competence. This is the intrinsic ability of a mosquito vector to support replication of a virus, leading to a disseminated infection of the salivary glands, whereby virus is expectorated upon blood feeding, culminating in a transmission event [6]. And while there are historical studies regarding DENV infection in humans [7, 8], there is less contemporary focus on the infectivity of humans to mosquitoes [9]. In this issue of The Journal of Infectious Diseases, Whitehorn et al present the first direct comparison of Aedes aegypti and Aedes albopictus acquisition potential by the simultaneous feeding on viremic individuals, with implications for the important transmission events listed above.