Seroprevalence of Powassan Virus in Healthy Central and Northeastern Minnesota Blood Donors

Abstract

Powassan virus is the only member of the tickborne encephalitis arboviral family present in North America. It is a flavivirus transmitted by Ixodes scapularis, the deer tick, and can cause severe, potentially fatal meningoencephalitis. Powassan has emerged as a national public health concern in the last sixty years, and as a local concern in Minnesota in the last five years. Here we show that Powassan exposure in 2009 had a much larger geographic and demographic range than indicated by clinical reporting of human cases. Potential exposures were identified in samples from northeastern Minnesota, particularly from St. Louis County. However, we also observed a number of exposures in the non-endemic metro area and surrounding suburbs, despite being early in the season. This suggests that “cabin culture,” the traffic of southern Minnesotans to cabins in north-central and northeast Minnesota, plays a role in non-endemic exposure rates. No significant risk was associated with a particular age group, although 66.7% (4 of 6 donors) of recent exposures were in donors younger than 25 years. More work needs to be done to determine the count of true Powassan infections, but the trends identified in the study appear to suggest that Powassan is positioned to become a significant public health threat similar to West Nile. Identification of the extent, direction, and speed of the emergence of Powassan will provide the framework for continued surveillance, educational research development, and analysis of potential economic impact.