Linking Bird and Mosquito Data to Assess Spatiotemporal West Nile Virus Risk in Humans.

West Nile virus (WNV; family Flaviviridae) causes a disease in humans that may develop into a deadly neuroinvasive disease. In North America, several peridomestic bird species can develop sufficient viremia to infect blood-feeding mosquito vectors without succumbing to the virus. Mosquito species from the genus Culex, Aedes and Ochlerotatus display variable host preferences, ranging between birds and mammals, including humans, and may bridge transmission among avian hosts and contribute to spill-over transmission to humans. In this study, we aimed to test the effect of density of three mosquito species and two avian species on WNV mosquito infection rates and investigated the link between spatiotemporal clusters of high mosquito infection rates and clusters of human WNV cases. We based our study around the city of Ottawa, Canada, between the year 2007 and 2014. We found a large effect size of density of two mosquito species on mosquito infection rates. We also found spatiotemporal overlap between a cluster of high mosquito infection rates and a cluster of human WNV cases. Our study is innovative because it suggests a role of avian and mosquito densities on mosquito infection rates and, in turn, on hotspots of human WNV cases.

Influence of Demography, Land Use, and Urban Form on West Nile Virus Risk and Human West Nile Virus Incidence in Ottawa, Canada.

Human infection by West Nile virus (WNV; family Flaviviridae), in some cases, develops into a deadly neuroinvasive disease. WNV risk is thought to be influenced by factors affecting the density of species that promote replication and transmission of the virus, namely peridomestic bird and mosquito species. Factors influencing contact between peridomestic bird and mosquito species and contact between infected mosquitoes and vulnerable human populations may also be important in determining WNV risk in an area. Several urban form and demographic factors, such as population density and the proportion of aged housing units, have been linked with increased WNV risk. Other factors, such as proportion of old-growth forest and wetlands, have been linked to decreased WNV risk. In this study, we aimed to test the effect of several demographic, land use, and urban form variables on WNV risk within neighborhoods of the city of Ottawa, Canada, based on the spatiotemporal clustering of infected mosquitoes and human WNV cases. We found a large positive effect of population density and proportion of aged housing units on WNV risk, using both entomological and epidemiological data. Interestingly, we found a large negative effect of proportion of natural areas in our epidemiological analysis, but not in our entomological analysis. Although our epidemiological data set was relatively small, these results suggest entomological surveillance results should be interpreted alongside other factors when investigating risk to humans. Our study is also one of the few to suggest an effect of demography, land use, and urban form on WNV risk in a Canadian urban center, using both entomological and epidemiological data.