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Delineating West Nile virus transmission cycles at various scales: the nearest neighbor distance-time model.
Introduction
Background West Nile Virus (WNV) is a vector-borne infectious disease spreading rapidly throughout the United States and exacting a high toll in terms of human and animal lives. It is transmitted to humans and other mammals by mosquitoes which acquire the virus by feeding on infected birds (CDC 1999; Rappole et al. 2000; CDC 2002; MDH 2003). Most people infected with WNV are asymptomatic or experience only a flu-like illness. In others, the virus causes West Nile fever (CDC 1999) and in some of these cases, the infected people develop West Nile encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord), both of which can be fatal (CDC 1999; Hayes et al. 2005; Grinev et al. 2006; Hayes 2007). The geographic distribution of WNV has expanded since its discovery in Uganda in 1937 and now includes all continents save for Australia and Antarctica (Hayes 2007). In the United States, the virus first appeared in the Bronx borough of New York in 1999 (CDC 1999) and since then, it has spread rapidly west and south, causing seasonal epidemics. It is challenging to predict and explain the spread of WNV because it propagates via complex interrelationships between human, avian, and mosquito habitat systems, which can luther be influenced by environmental, built-environment, and anthropogenic risk factors (Brownstein et al. 2002; Ruiz et al. 2004; Gibbs et al. 2006). This complexity has prompted both prospective and retrospective techniques to identify WNV exposure areas (Brownstein et al. 2002; Mostashari et al. 2003b; Theophilides et al. 2003; Ruiz et al. 2004; Bowman et al. 2005; Eidson et al. 2005; Cooke et al. 2006; Corrigan et al. 2006; Diuk-Wasser et al. 2006; Gibbs et al. 2006; Johnson et al. 2006; Tachiiri et al. 2006; Theophilides et al. 2006; David et al. 2007; Lian et al. 2007). The prospective techniques are mainly early warning approaches based on information on a single component of the WNV transmission cycle, i.e., either infected birds or human cases. In the retrospective group, the most common approach to delineate WNV exposure areas is the use of mathematical or statistical models, relating the incidence cases of either infected dead birds or human cases to a range of risk factors. Even though...See the full content of this document
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