title: Increased recognition of Powassan encephalitis in the United States, 1999-2005.
abstract: Powassan virus (POWV) disease is a rare human disease caused by a tick-borne encephalitis group flavivirus maintained in a transmission cycle between Ixodes cookei and other ixodid ticks and small and medium-sized mammals. During 1958-1998, only 27 POWV disease cases (mostly Powassan encephalitis) were reported from eastern Canada and the northeastern United States (average, 0.7 cases per year). During 1999-2005, nine cases (described herein) of serologically confirmed POWV disease were reported in the United States (average, 1.3 cases per year): four from Maine, two from New York, and one each from Michigan, Vermont, and Wisconsin. The Michigan and Wisconsin cases are the first ever reported from the north-central United States. Of these nine patients, 5 (56%) were men, the median age was 69 years (range: 25-91 years), and 6 (67%) had onset during May-July. All but one patient developed encephalitis with acute onset of profound muscle weakness, confusion, and other severe neurologic signs. In one case, no neurologic symptoms were present but the presence of pleocytosis, an elevated cerebrospinal fluid (CSF) protein concentration, and POWV-specific immunoglobulin M in CSF suggested neuroinvasion. All patients recovered from their acute disease, but most had long-term neurologic sequelae. Periresidential ecologic investigations were performed in three cases, including tests of local mammals and ticks for evidence of POWV infection. Woodchucks (Marmota monax), striped skunks (Mephitis mephitis), and a raccoon (Procyon lotor) collected at two of the Maine case-patients' residences had neutralizing antibody titers to POWV. I. cookei were found on woodchucks and skunks and questing in grassy areas of one of these residences; all were negative for POWV. Although POWV disease is rare, it is probably under-recognized, and it causes significant morbidity, and thus is an additional tick-borne emerging infectious disease entity. Because no vaccine or specific therapy is available, the basis of prevention is personal protection from ticks (or "tick hygiene") and reduced exposure to peridomestic wild mammals.
authors.affiliation: Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, U.S. Public Health Service, Department of Health and Human Services, Fort Collins, Colorado 80522, USA.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Hinten
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Beckett
authors.forename: Kathleen F
authors.initials: KF
authors.lastname: Gensheimer
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Pritchard
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Courtney
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Sears
authors.forename: John M
authors.initials: JM
authors.lastname: Woytowicz
authors.forename: David G
authors.initials: DG
authors.lastname: Preston
authors.forename: Robert P
authors.initials: RP
authors.lastname: Smith
authors.forename: Peter W
authors.initials: PW
authors.lastname: Rand
authors.forename: Eleanor H
authors.initials: EH
authors.lastname: Lacombe
authors.forename: Mary S
authors.initials: MS
authors.lastname: Holman
authors.forename: Charles B
authors.initials: CB
authors.lastname: Lubelczyk
authors.forename: Patsy Tassler
authors.initials: PT
authors.lastname: Kelso
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Beelen
authors.forename: Mary Grace
authors.initials: MG
authors.lastname: Stobierski
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Sotir
authors.forename: Susan
authors.initials: S
authors.lastname: Wong
authors.forename: Gregory
authors.initials: G
authors.lastname: Ebel
authors.forename: Olga
authors.initials: O
authors.lastname: Kosoy
authors.forename: Joseph
authors.initials: J
authors.lastname: Piesman
authors.forename: Grant L
authors.initials: GL
authors.lastname: Campbell
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Marfin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004675:Encephalitis, Tick-Borne / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D014481:United States / Q000453:epidemiology