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Proc Biol Sci. 2017 Feb 8;284(1848). pii: 20162078. doi: 10.1098/rspb.2016.2078.

Drought and immunity determine the intensity of West Nile virus epidemics and climate change impacts.

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Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 1156 High St, Santa Cruz, CA 95064, USA
Research Applications Lab, National Center for Atmospheric Research, 3450 Mitchell Ln, Boulder, CO 80301, USA.
Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, USA.
Department of Earth System Science and Woods Institute for the Environment, Stanford University, Stanford, CA 94305, USA.
Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Wadsworth Center, New York State Department of Health, Slingerlands, NY 12159, USA.
School of Public Health, Department of Biomedical Sciences, SUNY, Albany, NY 12201, USA.
Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 1156 High St, Santa Cruz, CA 95064, USA


The effect of global climate change on infectious disease remains hotly debated because multiple extrinsic and intrinsic drivers interact to influence transmission dynamics in nonlinear ways. The dominant drivers of widespread pathogens, like West Nile virus, can be challenging to identify due to regional variability in vector and host ecology, with past studies producing disparate findings. Here, we used analyses at national and state scales to examine a suite of climatic and intrinsic drivers of continental-scale West Nile virus epidemics, including an empirically derived mechanistic relationship between temperature and transmission potential that accounts for spatial variability in vectors. We found that drought was the primary climatic driver of increased West Nile virus epidemics, rather than within-season or winter temperatures, or precipitation independently. Local-scale data from one region suggested drought increased epidemics via changes in mosquito infection prevalence rather than mosquito abundance. In addition, human acquired immunity following regional epidemics limited subsequent transmission in many states. We show that over the next 30 years, increased drought severity from climate change could triple West Nile virus cases, but only in regions with low human immunity. These results illustrate how changes in drought severity can alter the transmission dynamics of vector-borne diseases.


Culex; disease ecology; global warming; nonlinear temperature–disease relationship; vector-borne disease

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