Clinical Signs and Symptoms of Powassan Virus Disease

Clinical presentation

Powassan virus disease should be considered in any person with an acute febrile or neurologic illness who has had recent exposure to ticks (primarily Ixodes scapularis, Ix. cookei, or Ix. marxi) in endemic areas. Other causes of encephalitis and aseptic meningitis should also be considered, as appropriate (e.g., herpes simplex viruses, enteroviruses, West Nile virus, St. Louis encephalitis virus, La Crosse virus, eastern equine encephalitis virus).

Powassan virus can rarely be transmitted through blood transfusion.

Signs and symptoms

Powassan virus infection can be asymptomatic or cause a non-specific febrile illness. Neuroinvasive disease can present as aseptic meningitis or encephalitis which can be severe. The incubation period for Powassan virus disease ranges from 1–5 weeks.

• Initial symptoms can include fever, headache, vomiting, and generalized weakness.
• The disease can progress to encephalitis, meningoencephalitis, or aseptic meningitis.
• Symptoms of encephalitis may include altered mental status, seizures, speech problems (aphasia, dysarthria), paresis or paralysis, movement disorders, and cranial nerve palsies.

Clinical assessment

Cerebrospinal fluid (CSF) findings include lymphocytic pleocytosis in the majority of patients with Powassan virus meningitis or encephalitis; neutrophils can predominate early in the disease. CSF protein is generally normal or mildly elevated, while glucose concentration is normal.

Electroencephalography (EEG) in patients with Powassan virus encephalitis reveals generalized slow wave activity, and results can resemble those seen in herpes simplex virus encephalitis. Magnetic resonance imaging (MRI) of the brain in patients with Powassan virus encephalitis can show hyperintensities in the superficial and deep white matter.

Outcomes

Approximately 10% of Powassan virus neuroinvasive disease cases are fatal and about half of survivors have long-lasting neurologic deficits, such as headaches, muscle weakness, focal paralysis, or cognitive difficulties.