Ecological Niche of the 2003 West Nile Virus Epidemic in the Northern Great Plains of the United States

Abstract

BackgroundThe incidence of West Nile virus (WNv) has remained high in the northern Great Plains compared to the rest of the United States. However, the reasons for the sustained high risk of WNv transmission in this region have not been determined. To assess the environmental drivers of WNv in the northern Great Plains, we analyzed the county-level spatial pattern of human cases during the 2003 epidemic across a seven-state region.Methodology/Principal FindingsCounty-level data on WNv cases were examined using spatial cluster analysis, and were used to fit statistical models with weather, climate, and land use variables as predictors. In 2003 there was a single large cluster of elevated WNv risk encompassing North Dakota, South Dakota, and Nebraska along with portions of eastern Montana and Wyoming. The relative risk of WNv remained high within the boundaries of this cluster from 2004–2007. WNv incidence during the 2003 epidemic was found to have a stronger relationship with long-term climate patterns than with annual weather in either 2002 or 2003. WNv incidence increased with mean May–July temperature and had a unimodal relationship with total May–July precipitation. WNv incidence also increased with the percentage of irrigated cropland and with the percentage of the human population living in rural areas.Conclusions/SignificanceThe spatial pattern of WNv cases during the 2003 epidemic in the northern Great Plains was associated with both climatic gradients and land use patterns. These results were interpreted as evidence that environmental conditions across much of the northern Great Plains create a favorable ecological niche for Culex tarsalis, a particularly efficient vector of WNv. Further research is needed to determine the proximal causes of sustained WNv transmission and to enhance strategies for disease prevention.

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

“…The high WNV rates in the Northern Great Plains region likely dampened potential significant clusters from other regions as the Anselin Local Moran's I test considers the global population mean in its local calculations. States in the northern Great Plains have been shown to have high WNV rates with consistent spatial clustering, especially in eastern Colorado and throughout Nebraska, South Dakota and North Dakota (Wimberly et al, 2008;Sugumaran et al, 2009;DeGroote and Sugumaran, 2012). South Dakota, in the Northern Great Plains region, has had the highest average incidence of WNV neuroinvasive disease in the USA since 2004 (Wimberly et al, 2013).…”

“…In Iowa, inconsistent inter-annual climatic relationships were found in relation to WNV incidence (DeGroote et al, 2008). In the Great Plains region, it was suggested that a May-July precipitation of approximately 200 mm reflects optimum conditions for WNV amplification (Wimberly et al, 2008). In Mississippi, an inverse relationship between countylevel WNV risk and total annual rainfall during the previous year was demonstrated (Wang et al, 2010).…”

Regional Differences in the Association Between Land Cover and West Nile Virus Disease Incidence in Humans in the United States

“…16 We recognize that there are compositional differences in land cover and human population between counties, but our data and that of other researchers in the field indicate that aggregating these data at a county resolution is a viable method for these analyses. 3,9,[17][18][19] Human disease case data (2002-2008) with a county resolution, including meningitis/encephalitis, WN fever, and other clinical/unspecified cases as defined by the Centers for Disease Control and Prevention (CDC), 20 were collated from the US Geological Survey Disease Maps webpage. 21 Alaska and Hawaii were excluded because human WNV disease cases have not been reported from these states.…”

Effects of weather and landscape on the equine West Nile virus infection risk in Mississippi, USA

“…Wimberly et al (2008) found a quadratic relationship between the rate of human WNv diseases in 2003 and May-July precipitation of 2002 in the Great Plains in USA, with the 2003 rate of human WNv diseases decreasing when total May-July precipitation reached beyond 200 mm. In addition, the land use and land cover of a region are unlikely to change at a large spatial scale in the short term (e.g., 1-2 years) unless catastrophic disasters occur.…”