Powassan Virus (POWV) is an arbovirus that may not be identified unless specific tests are performed.
Genus: Flavivirus
Vector: Ixodes ticks
Usual hosts: woodchucks, squirrels, chipmunks, groundhogs, white-footed mice
Distribution: northeastern United States, north central United States, Canada, Russia
Incubation period: 1 to 5 weeks
Clinical findings:
(1) fever
(2) myalgia with weakness
(3) encephalitis (decreased level of consciousness, memory loss, seizures, focal neurological findings)
(4) skin rash
(5) gastrointestinal symptoms (vomiting)
(6) sore throat
(7) acute flaccid paralysis
(8) severe neurological disease with death
Laboratory findings:
(1) CSF pleocytosis (up to 700 per µL)
(2) variable mild thrombocytopenia
The diagnosis is made based on:
(1) isolation of virus
(2) IgM antibodies on ELISA, confirmed by plaque neutralization test
(3) CSF IgM antibodies to Powassan antigen
(4) 4-fold rise in titer
(5) molecular method
