Powassan Virus Encephalitis, Minnesota, USA

Justin Birge

and Steven Sonnesyn

Author affiliations: Abbott Northwestern Hospital, Minneapolis, Minnesota, USA

Abstract

Powassan virus (POWV) is a rare tick-borne agent of encephalitis in North America. Historically, confirmed cases occurred mainly in the northeastern United States. Since 2008, confirmed cases in Minnesota and Wisconsin have increased. We report a fatal case of POWV encephalitis in Minnesota. POWV infection should be suspected in tick-exposed patients with viral encephalitis.

Case Report

A 67-year-old woman from Aitkin, Minnesota, USA, sought treatment at a local hospital on May 30, 2011, with a 3-day history of dizziness, fever of up to 103°F (39.4°C), chills, malaise, nausea, and occasional confusion with slurred speech. She had no respiratory or gastrointestinal symptoms and no history of ill contacts, travel, environmental exposures, or other recent illness. She had not been exposed to animals or vectors, other than those endemic to her area of residence, which included mosquitoes and deer ticks. She had removed many deer ticks after gardening or hiking in the woods. The patient’s past medical history was notable for colon cancer, which had been treated with a partial colectomy in October 2010 and chemotherapy through April 2011. She also had a history of hypertension, cutaneous lupus, and a remote cerebral aneurysm with surgical clipping. Medications she was taking were atenolol, hydroxychloroquine, and valsartan.
On admission, the woman was alert and reported mild neck tenderness. Her temperature was 100°F (37.8°C), blood pressure 138/77 mm Hg, pulse rate 83 beats/min, respiratory rate 22 breaths/min, and oxygen saturation 98% on room air. Results of neurologic, cardiac, and respiratory examinations were normal. Studies with normal test results included comprehensive metabolic panel, urinalysis, computed tomographic scan of the head, and chest radiograph. Results of serum screen for Borrelia burgdorferi antibodies (by ELISA) were negative. Leukocyte count was within reference range (10.8 × 10³/mm³), with neutrophil (polymorphonuclear leukocytes) predominance (80%). Her cerebrospinal fluid (CSF) showed 80 leukocytes (89% polymorphonuclear leukocytes), 5 erythrocytes, and 64 mg/dL of protein. The patient was given piperacillin/tazobactam and doxycycline.
The next day, she was less responsive and was transferred to Abbott Northwestern Hospital in Minneapolis. Shortly thereafter, she became unresponsive and labored breathing developed. Her temperature reached 102°F (38.9°C), and the following laboratory values were outside the reference range: leukocyte count (11.3 × 10³/mm³), sodium level (131 mmol/L), erythrocyte sedimentation rate (49 mm/h), and protein level (2.3 mg/dL). Neurology and infectious disease specialists suspected viral encephalitis. Magnetic resonance imaging (MRI) was deferred because of the unknown composition of the aneurysm clip, and the patient underwent a computed tomography angiogram of the head and neck. Infarction, vasculitis, meningeal enhancement, and structural abnormalities were not found. Twenty-four–hour electroencephalogram monitoring and administration of ceftriaxone (2 g intravenously [IV] every 24 h), acyclovir (500 mg IV every 8 h), and doxycycline (100 mg IV every 12 h) were initiated.
Overnight, the patient became apneic and required intubation. Examination revealed absent deep tendon reflexes, ocular deviation, positive Babinski response, and bilateral flaccid paralysis of the extremities. Pupillary light and corneal reflexes remained intact. No independent respirations were initiated. Complement levels were within reference range. No evidence of seizure was shown on electroencephalogram, although epileptiform discharges were seen. Given the severity of encephalopathy, prophylactic levetiracetam was initiated.