We expect that 1-2 counties will report human cases during the week beginning September 9th. At this point, our recommendation is to ensure data quality, both of human cases and mosquito infection data. According to historical data, about 10% of cases have yet to be transmitted by this point in the year, but many of those were in the late WNV year 2012. In some years, transmission has already essentially ceased by this point. We are waiting for the first cold snap to put out mosquito populations down for the winter, and some northern counties in nearby states have already seen weather cold enough to stop their WNV cycles.
Projected Cases for 2018
This week's estimate of total cases for 2018 is 123 cases, up just two cases from the 121 cases predicted last week. Nearly all of the year's cases have occurred by this point, so our estimates are extremely stable at this point. It is difficult to predict where and when the remaining transmission will occur, except to say that they are going to be relatively rare. The rest of the season will be characterized by cooler temperatures leading into Fall, which will put WNV down until 2019.
South Dakota State University has partnered with the South Dakota Department of Health to implement a program of West Nile virus (WNV) research that will support public health decision makers at the state level and mosquito control programs at the local level. Major activities include mosquito surveillance and testing for WNV, monitoring environmental risk factors using data from earth observing satellites, and using this information to predict the risk of WNV to humans across the state. This work is supported in part by a grant from the NASA Applied Sciences Public Health and Air Quality Program (NNX15AF74G).