Extreme Weather Events and Mosquito-Borne Illness: Temperatures as the Primary Driver of Human West Nile Virus in South Dakota, 2003-2017

After a massive West Nile virus (WNV) outbreak in South Dakota in 2003 (1040 cases), it seemed in some years that WNV might be on the brink of dying out in the state. In 2011, for example, the state only reported 2 cases. Yet in the warm 2012 there were 203 cases reported, and it became clear that human infections could be related to meteorological indices, especially recent temperatures. We examined human case data from 2003-2015 in a series of statistical models conditioned on remotely sensed meteorological data, and in 2016 created a series of weekly risk prediction documents for use by mosquito control and public health officials. Here we discuss the particular role of temperature in human WNV and examine the effects of record-breaking heat events in early 2016. Successes and failures of the modeling attempt are discussed, as well as any generalizable lessons learned. Early estimates for 2017 are also given.