Broad-scale climate drivers of a vector-borne disease expansion from Mexico into the United States

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Heather M. Savoy, USDA-ARS Jornada Experimental Range & Jornada Basin LTER, NM, Debra Peters, USDA ARS Jornada Experimental Range and Jornada Basin LTER Program, Las Cruces, NM, Amy R. Hudson, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ and Luis Rodriguez, ARS, USDA, Orient Point, NY

Background/Question/Methods
Vesicular Stomatitis (VS) is a vector-borne vesicular disease with livestock and wildlife hosts that causes trade-disrupting outbreaks in the western US on a quasi-decadal cycle. Previous phylogenetic analyses linked VS outbreaks in the US to viral lineages in endemic regions of southern Mexico. This study investigates the role of broad-scale climate drivers in the timing of the northward expansion across the Mexico-US border. The study area includes the US states of Texas, New Mexico, and Arizona plus their neighboring Mexican states. We used two approaches to elucidate the spatially-explicit relationship between the incursion of VS into the US and different climate variables: (1) historical records (75+ years) of VS outbreaks in the US and Mexico were compiled from literature and compared to climate data, and (2) monthly climate in the year preceding VS incursion into the US was compared between entry and non-entry years on a 0.5 degree grid. Significant climate patterns were then compared to climate indices driven by key teleconnections: the El Nino-Southern Oscillation (ENSO), the Pacific Decadal Oscillation, and the Atlantic Multidecadal Oscillation. These climate indices have all been identified previously as drivers of temperature, precipitation, and drought, and may provide seasonal-to-annual predictive power for incursion events.
Results/Conclusions
Climate patterns in northern Mexico preceding VS incursions into the US include higher precipitation in the previous fall and warmer temperatures in the spring. These climate patterns differ in their relationship with climate teleconnections where spring maximum temperatures are cooler (warmer) during El Nino (La Nina) events. Based on climate data from 1940-1999, predictions of annual VS entry risk align with the timing and inter-outbreak frequency of observed VS outbreaks in the US in the 2000s. Identifying the role of broad-scale climate in driving VS northward expansion compared with multi-year gaps between incursions in the US will allow prediction of future outbreaks in the US under a changing climate and can be used to guide outbreak mitigation efforts.