Population genetic data suggest a role for mosquito-mediated dispersal of West Nile virus across the western United States

Abstract

After introduction, West Nile virus (WNV) spread rapidly across the western United States between the years 2001 and 2004. This westward movement is thought to have been mediated by random dispersive movements of resident birds. Little attention has been placed on the role of mosquito vectors in virus dispersal across North America. The mosquito vector largely responsible for WNV amplification and transmission of WNV in the western USA is Culex tarsalis. Here we present population genetic data that suggest a potential role for C. tarsalis in the dispersal of WNV across the western USA. Population genetic structure across the species range of C. tarsalis in the USA was characterized in 16 states using 12 microsatellite loci. STRUCTURE and GENELAND analyses indicated the presence of three broad population clusters. Barriers to gene flow were resolved near the Sonoran desert in southern Arizona and between the eastern Rocky Mountains and High Plains plateau. Small genetic distances among populations within clusters indicated that gene flow was not obstructed over large portions of the West Coast and within the Great Plains region. Overall, gene flow in C. tarsalis appears to be extensive, potentially mediated by movement of mosquitoes among neighboring populations and hindered in geographically limited parts of its range. The pattern of genetic clustering in C. tarsalis is congruent with the pattern of invasion of West Nile virus (WNV) across the western United States, raising the possibility that movement of this important vector may be involved in viral dispersal.

Distribution and Phylogenetic Comparisons of a Novel Mosquito Flavivirus Sequence Present in Culex tarsalis Mosquitoes from Western Canada with Viruses Isolated in California and Colorado

“…tarsalis populations in North America. 24,25 This finding could explain why similar CLBOV genotypes have been identified in Manitoba and Colorado. Detailed genetic studies of CLBOVs from geographically isolated Cx.…”

Local host specialization, host-switching, and dispersal shape the regional distributions of avian haemosporidian parasites

“…Nevertheless, more studies are needed to identify vectors and reveal their contribution to host-parasite associations. Indeed, vector movement has been linked to pathogen spread in other systems (42), and such movement, along with changes in vectorhost associations (43), might facilitate parasite host-switching and dispersal. Interestingly, regional studies of ectoparasites of small mammals have shown that flea assemblages can differ more with increasing distance between sampling locations and with increasing differences between local habitat and climate characteristics, even on the same host species (44,45), perhaps because fleas are more exposed to the environment than haemosporidian parasites.…”

Exploratory Analysis of Dengue Fever Niche Variables within the Río Magdalena Watershed

“…The watershed is in close proximity to the equator, indicating a warmer climate, and well within the currently-documented latitude range of the Aedes aegypti mosquito [8]. The elevation of the watershed's mountain boundaries should naturally isolate the Aedes aegypti vector from external areas, providing a study area with limited external influence [41,42]. Due to its location on the western side of South America, it is also influenced by El Niño/La Niña seasonal variations.…”