Powassan encephalitis

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Powassan encephalitis
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a,b) Noncontrast, sagittal T1-weighted magnetic resonance image of brain with suspected Powassan virus encephalitis

Powassan encephalitis, caused by the Powassan virus (POWV), a flavivirus also known as the deer tick virus, is a form of arbovirus infection that results from tick bites. It can occur as a co-infection with Lyme disease since both are transmitted to humans by the same species of tick.[1] There has been a surge in the number of cases and geographic range in the last decade. In the United States, cases have been recorded in the northeast.[2] The disease was first isolated from the brain of a boy who died of encephalitis in Powassan, Ontario, in 1958.[3] The disease is a zoonosis, an animal disease, usually found in rodents and ticks, with spillover transmission to humans. The virus is antigenically related to the Far Eastern tick-borne encephalitis viruses.[4]

Signs and symptoms

Symptoms manifest within 7–10 days and include fever, headache, partial paralysis, confusion, nausea and even coma.[citation needed]


The diagnosis of Powassan encephalitis is based on the following:[5]


There is currently no established treatment.[6]


Half of all cases results in permanent neurological damage and 10-15% result in death.[citation needed]


  1. Caulfield, AJ; Pritt, BS (December 2015). "Lyme Disease Coinfections in the United States". Clinics in Laboratory Medicine. 35 (4): 827–46. doi:10.1016/j.cll.2015.07.006. PMID 26593260.
  2. "Cumulative human disease cases reported to CDC ArboNET for 2015". United States Geological Survey. Archived from the original on 2016-12-15. Retrieved 2015-11-27.
  3. McLEAN, DM; DONOHUE, WL (1 May 1959). "Powassan virus: isolation of virus from a fatal case of encephalitis". Canadian Medical Association Journal. 80 (9): 708–11. PMC 1830849. PMID 13652010.
  4. CASALS, J (13 February 1960). "Antigenic relationship between Powassan and Russian spring-summer encephalitis viruses". Canadian Medical Association Journal. 82: 355–8. PMC 1937779. PMID 13808112.
  5. Kapoor, Andrew K.; Zash, Rebecca (2022). "Powassan Virus". StatPearls. StatPearls Publishing. Archived from the original on 27 January 2022. Retrieved 30 October 2022.
  6. Hinten SR, Beckett GA, Gensheimer KF, et al. (December 2008). "Increased recognition of Powassan encephalitis in the United States, 1999-2005". Vector Borne Zoonotic Dis. 8 (6): 733–40. doi:10.1089/vbz.2008.0022. PMID 18959500.

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