Powassan Encephalitis: A Case Report from New York, USA

Background Powassan is a positive-sense, single-stranded, enveloped RNA virus that is a tick-borne Flavivirus, transmitted by Ixodes species, with groundhogs being the usual mammalian host. The virus is endemic to North America, with peak transmission during the summer and fall. The incubation period is 7–34 days, followed by a prodrome of flu-like symptoms. Although most infected individuals are asymptomatic, the virus can penetrate the CNS to produce a viral encephalitis. The key to the diagnosis is a positive serology. Results The patient is a 62-year-old male with a past history of a right putamen infarct, hepatitis C, hypertension, and substance abuse who presented due to acute onset altered mental status, dysarthria, and left-sided facial droop. He had several tick bites around the time of presentation in December. He was empirically treated for possible meningitis, as CSF revealed WBC 370 (80% mononuclear cells); RBC 10, protein 152 mg/dL, and glucose 59 mg/dL. An MRI scan of the brain showed a subacute left putamen stroke. MRAs of the head and neck were unremarkable. A Mayo Clinic Encephalopathy Panel was unremarkable; however, a New York State Arbovirus panel revealed Powassan IgM ELISA as well as Powassan Polyvalent microsphere immunofluorescence assay reactivity. His hospital course was complicated by critical illness myopathy and respiratory failure requiring tracheostomy. Conclusion The Powassan virus is a known etiology for encephalitis in North America. Although the peak incidence of transmission is in the summer and fall, this does not exclude transmission during other seasons. Due to the increasing prevalence of Powassan virus in Lyme-endemic areas particularly in the Midwest and Northeast, United States, patients with an unexplained altered mental status in these regions should be screened for Powassan virus, regardless of the time of year.


Background
Powassan is a positive-sense [1], single-stranded, enveloped RNA virus that is a tick-borne Flavivirus, transmitted by Ixodes species, with groundhogs and other small-to medium-sized forest rodents being the usual mammalian host [2][3][4]. is virus is endemic to North America, with peak transmission during the summer and fall, when the Ixodes tick is most active [4,5]. However, as temperatures continue to rise in endemic areas, it is anticipated that the rates of Powassan infection will also rise in other seasons, including the winter [6]. e incubation period is 7-34 days, followed by a prodrome of flu-like symptoms, consistently associated with headache and fever, lasting 1-3 days on average [7]. Despite the virus being highly neurotropic, the majority of patients who are infected with Powassan are asymptomatic [2]. When patients are symptomatic from Powassan virus, they will present with encephalitis and altered sensorium [2,4].
Routine laboratory studies are typically unremarkable; the cerebrospinal fluid will show a pleocytosis, which can be lymphocytic or polymononuclear predominant [2,8].
ere is insufficient data for standardized treatment, as the treatment is largely supportive. However, case reports suggest the usage of intravenous immunoglobulin and steroids [2,3].
Roughly, 50% of patients will have long term neurological sequelae of Powassan virus, such as recurrent headaches, cognitive disruption, and focal neurological deficits [5,9]. It is estimated that the 10% of patients with Powassan will expire from the disease [5,9].

Case Presentation
e patient is a 62-year-old male with a past medical history of a right putamen infarct, hepatitis C, hypertension, and substance abuse who initially presented due to altered mental status, dysarthria, and a left facial droop. He had several tick bites around the time of presentation in December.
His hospitalization course was complicated by a recurrent stroke; his repeat MRI brain 2 weeks after presentation revealed a small foci of acute infarct involving cerebellum, left basal ganglia, and splenium of corpus callosum ( Figure 2 Unfortunately, the patient required artificial airway and feeding access due to respiratory failure. At the time of discharge, notable neurological symptoms included global aphasia.

Discussion
Powassan virus is a known etiology for encephalitis in North America. Although the peak incidence of transmission of the virus is in the summer and fall when the Ixodes species is most active, this does not exclude transmission in other seasons [5]. As wintertime temperatures continue to rise in endemic areas, it can be anticipated that there will be greater tick activity and exposures in the winter [6]. is suggests that the infection rate will also rise, increasing the number of patients with Powassan virus.
Our patient's diagnosis demonstrates the importance of obtaining a thorough tick exposure history. Due to the increasing prevalence of Powassan virus in Lyme-endemic areas (particularly in the Midwest and Northeast, United States), some experts have suggested screening for Powassan virus in patients with unclear CNS phenomena in Lymeendemic areas, as the disease is underrecognized [5,10]. is further highlights the need for increased awareness and surveillance of Powassan infections [6].

Conclusion
is case highlights the importance of obtaining Powassan serology in a patient with an unexplained altered mental status. It also demonstrates the importance of testing for the  Data Availability e data for this article were gathered from the patient's medical record.

Consent
Informed consent was obtained from the patient's healthcare proxy, as the patient could not provide. An informed consent document was signed.

Conflicts of Interest
e authors declare that they have no conflicts of interest.