Strain-dependent assessment of Powassan virus transmission to deer ticks.

1.Powassan virus (POWV) is an emergent tick-borne encephalitis virus of Lyme disease endemic sites in North America. Due to range expansion and local intensification of deer tick vector (Ixodes scapularis) populations in the northeastern and upper midwestern U.S., encephalitis cases are increasingly being reported. A better understanding of the transmission cycle of POWV may allow for predicting the eventual public health burden. Recent phylogeographic analyses of POWV have identified geographical structuring, with well-defined northeastern and midwestern clades of the deer tick virus subtype (lineage II); sublineages exist within each clade. It may be that the local sublineages differ in their capacity to be transmitted by the deer tick vector. Accordingly, we determined whether there are strain-dependent differences in transmission. Five recent, low passage POWV isolates were used to measure aspects of vector competence, using viremic and artificial infection methods. Infection rates in experimental ticks remained consistent between all five isolates tested, resulting in 12-20% infection rate and no clear differences in viral load. We conclude that there is a genotype independent ability of POWV to infect deer ticks, and that differences in transmission efficiency are not likely to serve as the basis for regional differences in apparent public health burden.