Abstract
The northern Great Plains (NGP) of the United States has been a hotspot of West Nile virus (WNV) incidence since 2002. Mosquito ecology and the transmission of vector-borne disease are influenced by multiple environmental factors, and climatic variability is an important driver of inter-annual variation in WNV transmission risk. This study applied multiple environmental predictors including land surface temperature (LST), the normalized difference vegetation index (NDVI) and actual evapotranspiration (ETa) derived from Moderate-Resolution Imaging Spectroradiometer (MODIS) products to establish prediction models for WNV risk in the NGP. These environmental metrics are sensitive to seasonal and inter-annual fluctuations in temperature and precipitation, and are hypothesized to influence mosquito population dynamics and WNV transmission. Non-linear generalized additive models (GAMs) were used to evaluate the influences of deviations of cumulative LST, NDVI, and ETa on inter-annual variations of WNV incidence from 2004–2010. The models were sensitive to the timing of spring green up (measured with NDVI), temperature variability in early spring and summer (measured with LST), and moisture availability from late spring through early summer (measured with ETa), highlighting seasonal changes in the influences of climatic fluctuations on WNV transmission. Predictions based on these variables indicated a low WNV risk across the NGP in 2011, which is concordant with the low case reports in this year. Environmental monitoring using remote-sensed data can contribute to surveillance of WNV risk and prediction of future WNV outbreaks in space and time.
Highlights
West Nile virus (WNV) first appeared in the northeastern United States in 1999, and spread westward and southward after 2002 [1]
Relative spatial patterns of WNV risk in the northern Great Plains (NGP) have remained relatively stable over time, there has been considerable interannual variability in human WNV incidence, with disease outbreaks often occurring in different locations in different years [6]
Environmental Predictors We examined three environmental variables as predictors of WNV risk: land surface temperature (LST), the normalized difference vegetation index (NDVI) and actual evapotranspiration (ETa), all of which were derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing products
Summary
West Nile virus (WNV) first appeared in the northeastern United States in 1999, and spread westward and southward after 2002 [1]. WNV has been reported in every state in the conterminous U.S and become one of the most important vector-borne diseases due to its high human morbidity and impacts on avian populations [2,3]. In the northern Great Plains (NGP), WNV caused a significant outbreak in 2003, and since that time the region has remained a major hotspot for human disease [4,5]. Climatic variability is known to have strong influences on the dynamics of virus circulation, vector abundance, and avian communities, and may explain historical fluctuations of WNV risk in the NGP [7,8,9]. Understanding the climatic determinants of WNV disease can provide a basis for forecasting future disease risk based on lagged responses to antecedent environmental conditions
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