Powassan Virus Disease


Powassan virus

Where Found

Most cases have occurred primarily in northeastern states and the Great Lakes region. Less frequently, cases have been identified in Mid-Atlantic States.

Incubation Period

1–4 weeks

Signs and Symptoms

  • Fever, headache, vomiting, and generalized weakness
  • Usually progresses to meningoencephalitis. May include meningeal signs, altered mental status, seizures, aphasia, paresis, movement disorders, or cranial nerve palsies.

General Laboratory Findings

CSF findings include lymphocytic pleocytosis (neutrophils can predominate early), normal or mildly elevated protein, and normal glucose.

Laboratory Diagnosis

  • Primarily through testing available at CDC and selected state health departments; limited commercial testing.
  • Measurement of virus-specific IgM antibodies in serum or CSF. Cross-reaction with other flaviviruses (e.g., West Nile, dengue, or St. Louis encephalitis viruses) can occur; plaque reduction neutralization tests should be performed to confirm the diagnosis.
  • RT-PCR may detect viral RNA in acute CSF specimens or tissues, but this method should not be used to rule out the diagnosis, as antibodies are often present at the onset of neuroinvasive signs and symptoms. RT-PCR might be more appropriate for very acute samples or samples obtained from patients who are immunocompromised.


No specific antiviral treatment for Powassan virus disease is available. Patients with suspected Powassan virus disease should receive supportive care as appropriate.


Ebel GD. Update on Powassan virus: emergence of a North American tick-borne flavivirus. Annu Rev Entomol. 2010;55:95–110.

El Khoury MY, Camargo JF, White, JL, et al. Potential role of deer tick virus in Powassan encephalitis cases in Lyme disease-endemic areas of New York, USA. Emerg Infect Dis. 2013;19:1926–1933.

Hermance ME, Thangamani S. Powassan virus: an emerging arbovirus of public health concern in North America. Vector Borne Zoonotic Dis. 2017;17:453–462.

Hinten SR, Beckett GA, Gensheimer KF, et al. Increased recognition of Powassan encephalitis in the United States, 1999–2005. Vector Borne Zoonotic Dis. 2008;8(6):733–740.

Johnson DK, Staples JE, Sotir MJ, et al. Tickborne Powassan virus infections among Wisconsin residents. Wis Med J. 2010;109(2):91-7.

Krow-Lucal ER, Lindsey NP, Fischer M, Hills SL. Powassan virus disease in the United States, 2006-2016. Vector Borne Zoonotic Dis. 2018;18:286-90.

Piantadosi A, Rubin DB, McQuillen DP, et al. Emerging cases of Powassan virus encephalitis in New England: Clinical presentation, imaging, and review of the literature. Clin Infect Dis. 2016;62:707–713.

Taylor L, Condon T, Destrampe EM, et al. Powassan virus infection likely acquired through blood transfusion presenting as encephalitis in a kidney transplant recipient. Clin Infect Dis. 2021;72(6):1051-54.

Tutolo JW, Staples JE, Sosa L, et al. Notes from the field: Powassan virus disease in an infant—Connecticut, 2016. MMWR Morb Mortal Wkly Rep. 2017;66:408-9.