Abstract
Understanding the conditions underlying the proliferation of infectious diseases is crucial for mitigating future outbreaks. Since its arrival in North America in 1999, West Nile virus (WNV) has led to population-wide declines of bird species, morbidity and mortality of humans, and expenditures of millions of dollars on treatment and control. To understand the environmental conditions that best explain and predict WNV prevalence, we employed recently developed spatial modeling techniques in a recognized WNV hotspot, Orange County, California. Our models explained 85–95% of the variation of WNV prevalence in mosquito vectors, and WNV presence in secondary human hosts. Prevalence in both vectors and humans was best explained by economic variables, specifically per capita income, and by anthropogenic characteristics of the environment, particularly human population and neglected swimming pool density. While previous studies have shown associations between anthropogenic change and pathogen presence, results show that poorer economic conditions may act as a direct surrogate for environmental characteristics related to WNV prevalence. Low-income areas may be associated with higher prevalence for a number of reasons, including variations in property upkeep, microhabitat conditions conducive to viral amplification in both vectors and hosts, host community composition, and human behavioral responses related to differences in education or political participation. Results emphasize the importance and utility of including economic variables in mapping spatial risk assessments of disease.
Highlights
Understanding the environmental conditions that lead to infectious disease outbreaks, though challenging, is often crucial for management and control [1]
In attempting to predict test data not used in model construction, we were able to explain a maximum of 56% of the variation in West Nile virus (WNV) prevalence in 2008, 6% in 2004, and 34% in 2005
Economic variables explained the largest amount of variation in WNV prevalence in vector populations (Figure 1)
Summary
Understanding the environmental conditions that lead to infectious disease outbreaks, though challenging, is often crucial for management and control [1]. WNV has infected numerous vector and host species [2,3,4], leading to continentalwide declines in bird populations [5,6], an estimated 3 million infections [7] and thousands of deaths in human hosts, and the expenditure of millions of dollars on control and vaccination efforts [8]. These efforts have focused on disease ‘‘hotspots’’, where WNV-infected vectors (mosquitoes), primary hosts (birds), and secondary mammalian hosts (including humans) co-occur in close proximity. The seemingly unpredictable nature of localized outbreaks and the fact that high WNV incidence has been reported from across a broad range of ecological conditions [12,13,14,15] has made forecasting WNV hotspots virtually impossible [16,17]
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