LaDeau Shannon L, Calder Catherine A, Doran Patrick J, Marra Peter P
1Cary Institute of Ecosystem Studies, Millbrook, NY 12545 USA.
Smithsonian Migratory Bird Center, National Zoological Park, Washington, DC 20008 USA.
Ecol Res. 2011;26(5):909-916. doi: 10.1007/s11284-010-0725-z. Epub 2010 May 26.
West Nile virus (WNV) was first detected in the western hemisphere during the summer of 1999, reawakening US public awareness of the potential severity of vector-borne pathogens. Since its New World introduction, WNV has caused disease in human, avian, and mammalian communities across the continent. American crows () are a highly susceptible WNV host and when modeled appropriately, changes in crow abundances can serve as a proxy for the spatio-temporal presence of WNV. We use the dramatic declines in abundance of this avian host to examine spatio-temporal heterogeneity in WNV intensity across the northeastern US, where WNV was first detected. Using data from the Breeding Bird Survey, we identify significant declines in crow abundance after WNV emergence that are associated with lower forest cover, more urban land use, and warmer winter temperatures. Importantly, we document continued declines as WNV was present in an area over consecutive years. Our findings support the urban-pathogen link that human WNV incidence studies have shown. For each 1% increase in urban land cover we expect an additional 5% decline in the log crow abundance beyond the decline attributed to WNV in undeveloped areas. We also demonstrate a significant relationship between above-average winter temperatures and WNV-related declines in crow abundance. The mechanisms behind these patterns remain uncertain and hypotheses requiring further research are suggested. In particular, a strong positive relationship between urban land cover and winter temperatures may confound mechanistic understanding, especially when a temperature-sensitive vector is involved.
西尼罗河病毒（WNV）于1999年夏季首次在西半球被发现，这重新唤起了美国公众对媒介传播病原体潜在严重性的认识。自其传入新大陆以来，WNV已在整个大陆的人类、鸟类和哺乳动物群体中引发疾病。美洲乌鸦（）是WNV的高度易感宿主，在进行适当建模时，乌鸦数量的变化可作为WNV时空存在的替代指标。我们利用这种鸟类宿主数量的急剧下降，来研究美国东北部WNV强度的时空异质性，WNV最初就是在该地区被发现的。利用繁殖鸟类调查的数据，我们发现WNV出现后乌鸦数量显著下降，这与较低的森林覆盖率、更多的城市土地利用以及更温暖的冬季气温有关。重要的是，我们记录了随着WNV连续多年在一个地区存在，乌鸦数量持续下降的情况。我们的研究结果支持了人类WNV发病率研究所显示的城市与病原体之间的联系。城市土地覆盖率每增加1%，我们预计乌鸦数量的对数将比未开发地区因WNV导致的下降幅度再额外下降5%。我们还证明了冬季平均气温高于正常水平与WNV相关的乌鸦数量下降之间存在显著关系。这些模式背后的机制仍然不确定，并提出了需要进一步研究的假设。特别是，城市土地覆盖率与冬季气温之间的强正相关关系可能会混淆对机制的理解，尤其是当涉及到对温度敏感的媒介时。
