Landscape, demographic and climatic associations with human West Nile virus occurrence regionally in 2012 in the United States of America

Abstract

Abstract. After several years of low West Nile virus (WNV) occurrence in the United States of America (USA), 2012 witnessed large outbreaks in several parts of the country. In order to understand the outbreak dynamics, spatial clustering and landscape, demographic and climatic associations with WNV occurrence were investigated at a regional level in the USA. Previous research has demonstrated that there are a handful of prominent WNV mosquito vectors with varying ecological requirements responsible for WNV transmission in the USA. Published range maps of these important vectors were georeferenced and used to define eight functional ecological regions in the coterminous USA. The number of human WNV cases and human populations by county were attained in order to calculate a WNV rate for each county in 2012. Additionally, a binary value (high/low) was calculated for each county based on whether the county WNV rate was above or below the rate for the region it fell in. Global Moran's I and Anselin Local Moran's I statistics of spatial association were used per region to examine and visualize clustering of the WNV rate and the high/low rating. Spatial data on landscape, demographic and climatic variables were compiled and derived from a variety of sources and then investigated in relation to human WNV using both Spearman rho correlation coefficients and Poisson regression models. Findings demonstrated significant spatial clustering of WNV and substantial inter-regional differences in relationships between WNV occurrence and landscape, demographic and climatically related variables. The regional associations were consistent with the ecologies of the dominant vectors for those regions. The large outbreak in the Southeast region was preceded by higher than normal winter and spring precipitation followed by dry and hot conditions in the summer.

The Recent Update of the Situation of West Nile Fever among Equids in Egypt after Three Decades of Missing Information

“…The virus is transmitted by mosquitoes as biological vectors, birds as a natural reservoir, and equines and humans representing dead-end hosts (Calistri et al, 2010;Benjelloun et al, 2017). The temperature plays an important role in speeding the cycle, the transmission period, as well as on the survival of mosquitoes (Elhaig et al, 2017;Selim et al, 2018); whenever the local ecological conditions are appropriate for viral amplification, humans and equines could easily be infected (Komar et al, 2001;DeGroote et al, 2014). Mosquitoes, especially Aedes, Ochlerotatus, and Culex species, transmit WNV, which rapidly spread throughout the US following its introduction in the late 1990s (CDC 2018).…”

Increased Human Incidence of West Nile Virus Disease near Rice Fields in California but Not in Southern United States

“…Urbanization has been associated with higher WNV seroprevalence in wild bird and mammal populations, 16,17 and higher human disease incidence on a county scale in the eastern and central regions of the US. [18][19][20][21] This is thought to be due to urbanization increasing larval habitat for container-breeding vectors of WNV including Culex pipiens and Culex quinquefasciatus. [22][23][24] In the western US, grassland and agricultural land covers have been associated with higher human WNV disease incidence.…”

Fine-scale wetland features mediate vector and climate-dependent macroscale patterns in human West Nile virus incidence

“…Although we did not detect this pattern, we cannot rule out the possibility that short-term wet periods occurred subsequent to drought in our study because we used a three-month resolution to define drought over 11 years (compared to bi-weekly water table depth changes over 3 years in Shaman et al 2005). However, results from western Colorado, New Jersey, and the southeastern United States indicate that dry climate conditions may be associated with higher human WNV incidence without subsequent precipitation (Shaman et al 2010;Johnson and Sukhdeo 2013;DeGroote et al 2014). These studies suggest that regional factors such as differences in wetland composition, or the predominant host and vector species could explain why post-drought re-inundation plays a role in the Shaman et al (2005) study in Florida, but not across our study area.…”