Relationships Among Snow Depth, Snow Water Equivalent, Streamflow and Virus Activity in Two Colorado Subwatersheds, 2004 to 2016

Vesicular stomatitis (VS) is the most common vesicular disease affecting livestock (domestic horses, cattle, pigs) throughout the Americas. VS is a vector-borne disease with more than >1500 infected premises in the western US from 2004-2016. The ecology of the host-vector-virus-environment system is the subject of a large, collaborative USDA research effort. Initial findings indicate VS incidents were spatially distributed near the stream network and temporally related to streamflow conditions with all first incidents (n=35) occurring following peak annual streamflow. These spatial and temporal relationships showcase the importance of hydrological contributions to the emergence and distribution of VS and indicate that snow conditions may play an important role in VS emergence. Peters et al. (2017) report that VS infected premises can be evaluated based upon outbreak (2004, 2014) and expansion (2005, 2015) years. Here we evaluate the relationships between monthly snow depth, snow water equivalent, streamflow and the number of VSV infected equine premises in two watersheds (Big Thompson and Saint Vrain) with a high number VS infected premises. The water content of snowpack and snow depth within both watersheds the months prior to a VS outbreak were both lower (2004) and higher (2014) than years with no infected premises. Conversely, outbreak years had higher autumnal and late season monthly streamflow than years with few or no VS infected premises. The complex water management system of reservoirs and irrigation canals along the Front Range of Colorado and VS vectors may buffer the relationship between SWE, snow depth and virus transmission observed in other locations. More detailed analyses of water conveyance associated with VS infection is needed in these watersheds to evaluate the impacts of local water conditions on the vector-host relationship, particularly related to observed elevated autumnal and summer streamflow co-occurring during outbreak years. (KEYWORDS: vesicular stomatitis, snow water equivalent, host-vector-virus-environment system, water management, virus transmission)