Linking the vectorial capacity of multiple vectors to observed patterns of West Nile virus transmission.
Abstract
Theoretical models suggest that increased vector species participation in pathogen transmission significantly increases the prevalence of vector and host infections. However, there has been a lack of empirical evidence to support this. We linked transmission potential of multiple vector species to observed patterns of enzootic pathogen transmission by conducting longitudinal field surveillance of West Nile virus (WNv) infections in Culex spp. mosquitoes and avian host communities in the southeast U.S. We then used a temperature-dependent vectorial capacity model as a predictor of WNv infections in mosquitoes and birds using general linear mixed effects models. Two WNv-competent Culex spp. mosquitoes were present in our study sites, Culex restuans Theobald during the spring and Culex quinquefasciatus Say during the summer. Empirical evidence of WNv transmission was limited exclusively to time periods when night time temperatures were suitable for accelerated within-vector viral replication, susceptible avian hosts (i.e. hatch year birds) were abundant and Cx. quinquefasciatus was the primary Culex spp. vector in the mosquito community. Contrary to theoretical predictions, increased presence of competent vector species through time did not significantly increase the prevalence of infections in the WNv enzootic system. Synthesis and applications. We extend a common theoretical model to both estimate the transmission potential of a mosquito community for West Nile virus (WNv) and quantify the relative contribution of two Culex mosquito species (Culex quinquefasciatus and Culex restuans) to observed patterns of WNv in the southeast U.S. Our findings suggest that to reduce the risk of human exposure to WNv in urban environments, vector control should focus on the primary WNv vector, Cx. quinquefasciatus. Additionally, vector control may be more effective if it coincides with the onset of the avian breeding season, when most WNv amplification occurs. Moreover, our results highlight relevant knowledge gaps pertaining to WNv transmission by secondary mosquito species that coexist either in time or space with Cx. quinquefasciatus. A better understanding of secondary WNv vector species is greatly needed in order to appropriately gauge their role in pathogen transmission dynamics.