4 cases of Powassan virus encephalitis


Powassan virus (POWV) can cause a rare but potentially life-threatening disease including encephalitis. In this case review, the authors describe 4 patients with Powassan virus encephalitis, who were all treated at a hospital in North Dakota. The patients resided in North Dakota and Wisconsin.

Powassan virus (POWV) can cause severe disease, including infection of the brain (encephalitis) or infection of the membranes around the brain and spinal cord (meningitis). Symptoms may include confusion, loss of coordination, difficulty speaking, and seizures. An estimated 1 out of 10 people with POWV encephalitis or POWV meningitis will die from the disease, according to the CDC.¹

The study entitled “Powassan virus infection: case series and literature review from a single institution,” by Raval and colleagues, highlights the increased spread of this tick-borne infection, particularly in the central north United States, and the need for clinicians to be aware of its varied clinical presentations.²

18-year-old male with single seizure

The young man presented to the hospital with a 2-day history of headaches and a single episode of seizure.

“He was at work, cutting trees, and was suspended from a harness, where he suddenly experienced clenching of his right upper extremity.”

CT scan was unremarkable. Treatment was not prescribed, since the man experienced only an isolated seizure.

“He subsequently developed right-sided weakness, worsening headaches, and somnolence and was subsequently transferred to our facility to receive a higher level of care,” the authors wrote.

Despite treatment, the young man’s headaches continued to worsen. At this point, he reported to the clinicians that he previously had a tick bite. He was then prescribed antibiotics including ceftriaxone, vancomycin, ampicillin, acyclovir and doxycycline.

Testing for the more common tick-borne infections, such as Lyme disease and anaplasmosis, was negative. However, the man had a positive serum analysis for Powassan virus immunoglobulin M.

“During his follow-up visit, he did not report any focal neurological deficits, seizures, or headaches.”

READ MORE: What is Powassan Virus?

60-year-old male with brain hemorrhage

The patient was admitted to the emergency department with fevers, headaches and dizziness. However, his examination was unremarkable and he was discharged.

On the way home, “he lost consciousness and was found obtunded and unresponsive,” according to the authors.

The man was intubated and transferred to the ICU.  A CT scan of the brain revealed intraparenchymal hemorrhage with a subdural hematoma.

After 7 days, the patient was stabilized and extubated. Although the man did not have focal neurological deficits, he did exhibit altered mental status, memory loss and anhedonia with depression.

The man later tested positive for Powassan virus and was treated symptomatically.

“His neurological function recovered with return of his baseline functional status on further follow-up,” the authors wrote.

61-year-old male with altered mental status

A 61-year-old man, from northwestern Minnesota, presented to the hospital with progressive headaches, body aches, high-grade fever, and altered mental status.

He enjoyed outdoor activities and reported having frequent tick bites.

The patient was initially treated with ceftriaxone, vancomycin and doxycycline. But testing for Lyme disease, anaplasmosis and ehrlichiosis were negative.

The man’s condition deteriorated and he was intubated and placed on a ventilator.

“Antibiotics were changed to vancomycin, acyclovir, piperacillin/tazobactam and micafungin,” the authors wrote.

His CSF analysis was positive by PCR and the man was diagnosed with Powassan virus encephalitis.

The “patient stayed in rehabilitation facility for over a month and eventually showed gradual improvement and was discharged home,” according to the authors.

69-year-old male with difficulty walking

A 69-year-old man with a history of tick bites was admitted to the emergency room with progressive weakness, headaches and fevers.

“He was diagnosed with a urinary tract infection and was treated with ciprofloxacin,” according to the authors.

However, his symptoms worsened. He continued having fevers, weakness and difficulty walking and reportedly had uncontrollable movements of his limbs.

An infectious work-up was negative, which included testing for tick-borne diseases. But he was empirically treated with IV doxycycline and gradually improved, regaining his strength.

Three weeks after he was admitted to the hospital, he tested positive for Powassan virus.

“He continued to improve neurologically,” the authors wrote. However, 4 months after his hospitalization, “he continued to have quadriceps muscle weakness and requires use of arm to get up from chair and with restriction of range of motion of lower limb at knee joint due to his weakness.”

Authors conclude:

“This study serves to highlight the increased detection of Powassan virus infection in the central north United States.”

“There is a need for clinician vigilance and public attention due to its increasing detection, westward progression and varied clinical presentations.”


  1. Centers for Disease Control and Prevention. https://www.cdc.gov/powassan/symptoms
  2. Raval M, Singhal M, Guerrero D, Alonto A. Powassan virus infection: case series and literature review from a single institution. BMC Res Notes. 2012 Oct 30;5:594. doi: 10.1186/1756-0500-5-594. PMID: 23111001; PMCID: PMC3506459.

No Replies to "4 cases of Powassan virus encephalitis"

    Join the Lyme Conversation
    (Note: comments are moderated. You will see your comment after it has been reviewed.)

    Some html is OK