In North America, two important and persistent mosquito-borne pathogens, Eastern Equine Encephalitis virus (EEEV) and West Nile virus (WNV), inflict serious human and economic costs and may be driven by environmental factors like land-cover and weather conditions. More specifically, previous studies suggest that outbreaks may be linked to wetlands because they provision important habitat for vectors and susceptible hosts. However, wetlands are not homogeneous and can vary substantially in terms of their vegetation, connectivity, size, and hydrology-driven inundation patterns. Therefore, we investigate links between specific wetland characteristics, vector abundance, and vector WNV and EEEV infection. We also asses how these relationships change across spatial scales extending 50m–5000m from wetlands and at time periods ranging from 1–12 months prior to the transmission season. We accomplish this with Generalized Additive Models assessing monthly mosquito surveillance data from 2001–2014 at 97 Connecticut sites.
Our results indicate that several wetland characteristics have important influences on vector populations. In particular, wetland vegetative characteristics had strong associations with vector abundance and vector infection. This is likely because vegetation imposes important constraints on the suitability of wetland habitats for vector larval development and on where contact between vectors and susceptible avian hosts occurs. We also found that wetland inundation characteristics combined with extreme hydrological wetness conditions (both very dry and wet) at several different time points resulted in significant increases in both vector infection and vector abundance. Further, the strongest relationships were detected at broad scales, 1000m–5000m from wetland edges. Therefore, we conclude that wetland characteristics, particularly vegetation and inundation, likely mediate shifts in the composition of host and mosquito populations in broad areas around wetlands, resulting in the observed changes in vector populations. These results expand the broad-scale understanding of wetland effects on WNV and EEEV transmission and help to explain erratic and deadly patterns of outbreak.