Skip directly to search Skip directly to A to Z list Skip directly to page options Skip directly to site content

Volume 19, Number 4—April 2013


Powassan Virus Encephalitis, Minnesota, USA

Cite This Article


Highlight and copy the desired format.

EID Neitzel DF, Lynfield R, Smith K. Powassan Virus Encephalitis, Minnesota, USA. Emerg Infect Dis. 2013;19(4):686.
AMA Neitzel DF, Lynfield R, Smith K. Powassan Virus Encephalitis, Minnesota, USA. Emerging Infectious Diseases. 2013;19(4):686. doi:10.3201/eid1904.121651.
APA Neitzel, D. F., Lynfield, R., & Smith, K. (2013). Powassan Virus Encephalitis, Minnesota, USA. Emerging Infectious Diseases, 19(4), 686.

To the Editor: Birge and Sonnesyn report the first death of a Minnesota resident caused by Powassan virus (POWV) (1). However, they provide an inaccurate description of several critical diagnostic and surveillance issues concerning POWV.

The 17 POWV infections detected in Minnesota residents from 2008 through 2011 (6 cases were identified through 2010, not 8 as reported by Birge and Sonnesyn) (Minnesota Department of Health [MDH], unpub. data) were found through enhanced surveillance. Health alerts to Minnesota medical providers described POWV as a possible etiologic agent for viral meningitis and encephalitis. Providers consulted with MDH on suspected cases and submitted serum and cerebrospinal fluid specimens to MDH. MDH conducted serologic testing for endemic arboviruses (including POWV) and reverse transcription PCR (RT-PCR) for flaviviruses and POWV. MDH would not have detected any POWV infections without enhanced surveillance. Limited field studies also identified POWV-infected ticks in 4 Minnesota counties (not 2 as reported [1]) (MDH, unpub. data).

Commercial laboratories do not provide testing for POWV, and only a few state health department laboratories and the Centers for Disease Control and Prevention offer testing. Serologic testing (enzyme immunoassay with plaque-reduction neutralization testing confirmation) is preferred (2) because POWV RT-PCRs are not validated, and the short viremic periods of flaviviruses limit their usefulness (3).

Few POWV infections are identified by lineage (prototype vs. deer tick virus); Minnesota’s first case in 2008 was identified as a deer tick virus infection, but the lineage was unknown for the other 16 cases. However, many case-patients had likely exposure to Ixodes scapularis ticks (blacklegged ticks), the tick species associated with deer tick virus transmission, and viruses from all POWV-positive tick pools were confirmed as deer tick virus by sequencing. The distribution of the 2 lineages in North America is poorly understood, and most cases likely go undetected without specific POWV surveillance efforts.

David F. NeitzelComments to Author , Ruth Lynfield, and Kirk Smith

Author affiliations: Minnesota Department of Health, St. Paul, Minnesota, USA


  1. Birge J, Sonnesyn S. Powassan virus encephalitis, Minnesota, USA. Emerg Infect Dis. 2012;18:166971. DOIPubMed
  2. Hinten SR, Beckett GA, Gensheimer KF, Pritchard E, Courtney TM, Sears SD, Increased recognition of Powassan encephalitis in the United States, 1999–2005. Vector Borne Zoonotic Dis. 2008;8:73340 . DOIPubMed
  3. Lanciotti RS. Molecular amplification assays for the detection of flaviviruses. Adv Virus Res. 2003;61:6799. DOIPubMed
Cite This Article

DOI: 10.3201/eid1904.121651

Related Links

Table of Contents – Volume 19, Number 4—April 2013


Please use the form below to submit correspondence to the authors or contact them at the following address:

David F. Neitzel, Minnesota Department of Health, Infectious Disease Epidemiology, 625 Robert St N, PO Box 64975, St. Paul, MN 55164, USA

character(s) remaining.

Comment submitted successfully, thank you for your feedback.