Powassan (POW) virus, a North American tick-borne
flavivirus related to the Eastern Hemisphere's tick-borne
encephalitis viruses, was first isolated from a patient with
encephalitis in 1958. From 1958-1998, 27 human POW encephalitis
cases were reported from Canada and the northeastern United
States. From September 1999-July 2001, four Maine and Vermont
residents with encephalitis were found to be infected.
There is no vaccine or specific therapy for