Can Powassan Virus Cause Encephalitis? A New York Case Report

Powassan virus encephalitis can cause severe brain inflammation
Symptoms include confusion, weakness, and altered mental status
Neurologic complications may persist despite supportive treatment

Powassan virus is a rare tick-borne flavivirus transmitted primarily by Ixodes ticks. While most infections are asymptomatic or cause only mild illness, some patients develop meningitis or encephalitis with serious neurologic complications.Because there is no approved antiviral treatment, early recognition and supportive care remain essential. Learn more about Powassan virus and how it is transmitted.

Clinical perspective: Although Powassan virus is an important tick-borne infection to recognize, I have not diagnosed a case in my outpatient Lyme disease practice. PPatients with Powassan encephalitis usually require hospitalization because of severe neurologic symptoms, and diagnosis is often made in the emergency department or inpatient setting.

The following case illustrates how severe Powassan encephalitis can present, even during the winter months.

In their article “Powassan Encephalitis: A Case Report from New York, USA”, Bazer and colleagues describe a man who was admitted to the hospital in December with altered mental status, dysarthria, and a left facial droop.¹

The patient also had multiple underlying medical conditions, including a prior right putamen infarct, hepatitis C, hypertension, and a history of substance abuse.

Because he reported several recent tick bites, clinicians considered a tick-borne infection as part of the diagnostic evaluation.

Powassan virus can cause severe neurologic disease

Most people infected with Powassan virus never develop symptoms. However, symptomatic infection can progress to meningitis or encephalitis, leading to confusion, altered consciousness, focal neurologic deficits, seizures, and other serious complications.

A 2023 systematic review of 84 published cases found that Powassan virus infection is associated with substantial neurologic morbidity. Persistent deficits included paralysis, cognitive impairment, speech disorders, cranial nerve involvement, and ataxia, particularly among patients with encephalitis.

Many patients require prolonged rehabilitation because recovery may take months, and some neurologic deficits can be permanent.

Published series report mortality rates ranging from approximately 10% to 20%, with older adults at the greatest risk of severe disease.

A lumbar puncture revealed cerebrospinal fluid pleocytosis and elevated protein levels. While awaiting diagnostic results, the patient was empirically treated with ceftriaxone and acyclovir for possible bacterial or viral meningitis.

His neurologic condition worsened, requiring intubation for airway protection. The hospitalization was further complicated by a recurrent stroke and the eventual need for a feeding tube.

READ: What Is the Powassan Virus?

Electrodiagnostic testing revealed nerve involvement

The patient also developed evidence of peripheral nerve injury. Electromyography (EMG) and nerve conduction studies (NCS) demonstrated generalized axonal loss with demyelinating polyradiculopathy.

Because of the demyelinating features, he received two courses of intravenous immune globulin (IVIG).

Powassan virus can occur outside the typical tick season

The authors emphasized that although Powassan virus transmission occurs most often during the summer and fall when Ixodes ticks are most active, clinicians should not exclude the diagnosis during other seasons if the clinical presentation and exposure history are suggestive.

Testing ultimately confirmed active Powassan virus infection in the cerebrospinal fluid, establishing the diagnosis of Powassan encephalitis. DDiagnosis typically relies on Powassan virus IgM antibody testing in serum or cerebrospinal fluid, with confirmatory testing performed through specialized public health laboratories.

At the time of discharge, the patient had persistent global aphasia. The case report did not determine whether the aphasia resulted primarily from Powassan encephalitis, the recurrent stroke, or both.

Supportive care remains the primary treatment

There is currently no specific antiviral treatment for Powassan virus infection. Antibiotics are not effective because Powassan virus is caused by a virus rather than bacteria. Management focuses on supportive care, which may include hospitalization, airway protection, seizure management, rehabilitation, and treatment of complications. Some patients receive corticosteroids or intravenous immune globulin (IVIG), but evidence supporting these therapies remains limited.

Frequently Asked Questions

Can Powassan virus cause encephalitis?

Yes. Although most infections are asymptomatic, Powassan virus can invade the central nervous system and cause meningitis or encephalitis, resulting in confusion, altered mental status, seizures, and focal neurologic deficits.

What are the symptoms of Powassan encephalitis?

Symptoms may include fever, headache, confusion, weakness, dysarthria, altered consciousness, seizures, focal neurologic deficits, and other signs of brain inflammation.

How is Powassan virus diagnosed?

Diagnosis is based on compatible clinical findings, a history of tick exposure, and laboratory testing. Cerebrospinal fluid analysis often shows pleocytosis and elevated protein, while specialized serologic or molecular testing confirms Powassan virus infection.

Can people recover from Powassan virus?

Many patients recover, but recovery may be slow. Some survivors experience persistent neurologic symptoms, including weakness, speech problems, cognitive impairment, or difficulty walking, while others regain much or all of their function with rehabilitation.

Clinical Takeaway

This case illustrates that Powassan virus should be considered in patients from tick-endemic regions who present with unexplained encephalitis, altered mental status, or focal neurologic deficits—even during the winter months if there is a history of tick exposure.

Although rare, Powassan encephalitis should be considered in patients with unexplained encephalitis and recent tick exposure, as early diagnosis can guide supportive management and rehabilitation planning.

Related Articles

What Is Powassan Virus?
Powassan Virus Infection Causes Polio-Like Illness
Fatal Powassan Virus Infection: A Case Report

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Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention