Abstract
Mosquito-borne West Nile virus (WNV) is the causative agent of West Nile disease in humans, horses, and some bird species. Since the initial introduction of WNV to the United States (US), approximately 30,000 horses have been impacted by West Nile neurologic disease and hundreds of additional horses are infected each year. Research describing the drivers of West Nile disease in horses is greatly needed to better anticipate the spatial and temporal extent of disease risk, improve disease surveillance, and alleviate future economic impacts to the equine industry and private horse owners. To help meet this need, we integrated techniques from spatiotemporal epidemiology, eco-phylogenetics, and distributional ecology to assess West Nile disease risk in horses throughout the contiguous US. Our integrated approach considered horse abundance and virus exposure, vector and host distributions, and a variety of extrinsic climatic, socio-economic, and environmental risk factors. Birds are WNV reservoir hosts, and therefore we quantified avian host community dynamics across the continental US to show intra-annual variability in host phylogenetic structure and demonstrate host phylodiversity as a mechanism for virus amplification in time and virus dilution in space. We identified drought as a potential amplifier of virus transmission and demonstrated the importance of accounting for spatial non-stationarity when quantifying interaction between disease risk and meteorological influences such as temperature and precipitation. Our results delineated the timing and location of several areas at high risk of West Nile disease and can be used to prioritize vaccination programs and optimize virus surveillance and monitoring.
Highlights
Mosquito-borne West Nile virus (WNV) is the causative agent of West Nile disease in humans, horses, and some bird species [1,2,3]
The WNV surveillance covariate was found to be an important predictor of West Nile disease (WND) risk with increased virus detection probability corresponding to increased disease risk (Table 1)
Since initial invasion by WNV in 1999, approximately 30,000 horses in the United States (US) have been affected by neurologic disease and hundreds more are infected by the virus each year
Summary
Mosquito-borne West Nile virus (WNV) is the causative agent of West Nile disease in humans, horses, and some bird species [1,2,3]. The virus is a member of the Flaviviridae family and belongs to the same sero-group as the arthropod-borne viruses (arboviruses). WNV is the most common cause of neuroinvasive arboviral disease in the contiguous US: the average human incidence was recently estimated by Curren et al [8]. To be 0.44 cases/100,000 persons and we [9] calculated estimates approximately 10% higher at 0.48 cases/100,000 after accounting for uneven reporting and environmental risk factors. Less is known about risk factors contributing to WNV infection of horses. In the years immediately following the 1999 US introduction of WNV, equine WNV vaccines were rapidly developed and licensed [10,11]: despite the initial post-invasion push to reduce what can be substantial economic impacts to horse owners, there has yet to be a large-scale, comprehensive analysis of equine West Nile disease (WND) in the US [12,13,14]
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