Powassan Virus Disease


Powassan virus

Where Found

Powassan virus infections have been recognized in the United States, Canada and Russia. In the United States, cases have been reported primarily from northeastern states and the Great Lakes region.

Incubation Period

1–4 weeks

Signs and Symptoms

  • Fever, headache, vomiting, and generalized weakness
  • Usually progresses to meningo encephalitis. 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 the sensitivity is unknown and this method should not be used to rule out the diagnosis.


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


Centers for Disease Control and Prevention. West Nile virus and other nationally notifiable arboviral diseases—United States, 2016. MMWR 2018;67(1);13-17.

Centers for Disease Control and Prevention. Outbreak of Powassan encephalitis—Maine and Vermont, 1999–2001. MMWR 2001;50(35):761–764.

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.

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.