Powassan virus (POWV) belongs to the group of flaviviruses, and is a rare but possibly fatal cause of tick-borne encephalitis (TBE) in the Northeastern United States (New York, Minnesota, Wisconsin, Michigan, Maine, Vermont, Connecticut, Massachusetts, and Pennsylvania), Canada (Ontario, Quebec, and New Brunswick provinces), and certain parts of Russia [1] [2] [3] [4]. The virus possesses two distinct lineages, both being transmitted from a stable animal reservoir consisting of rodents (eg. white-footed mice) and medium-sized mammals (eg. woodchucks, red squirrels groundhogs, skunks) onto the Ixodes ticks, one of the most important tick species related to human diseases [3] [5] [6]. Reports have shown that only 15 minutes are sufficient for the tick to transmit the virus to the host once it attaches to the skin [1] [4]. Wide-scale epidemiologic studies have established that many patients (due to undisclosed reasons) have an asymptomatic form of POWV infection, but in some patients, infection of the central nervous system (CNS), known as Powassan encephalitis, can develop [2] [4]. The period between the tick bite and the appearance of symptoms (known as the incubation period) typically lasts between 1-5 weeks and a prodromal period of 1-2 days, comprised of nonspecific respiratory and constitutional complaints (fever, malaise, headaches), is common [1] [2] [4]. Soon after, severe deterioration characterized by ataxia, weakness, hemiplegia, ophthalmoplegia, confusion, somnolence and a severely altered level of consciousness, as well as seizures and other focal neurological deficits, are observed in the case of Powassan encephalitis [1] [4] [6]. In addition, gastrointestinal irritation and skin rash may be seen [4]. The mortality rates of Powassan encephalitis range from 10-15% and residual neurological impairment (hemiplegia, paresis of the lower extremities, and deficits in memory and other cognitive skills) is noted in up to 50% of patients who survive the infection [2] [4] [6].

• Fever

  Abstract This article discusses two tick-borne illnesses: Powassan encephalitis, a rare cause of central nervous system infection caused by the Powassan virus, and Colorado tick fever, an acute febrile illness caused by the Colorado tick fever virus common [ncbi.nlm.nih.gov]

  […] nervous system infection caused by the Powassan virus, and Colorado tick fever, an acute febrile illness caused by the Colorado tick fever virus common to the Rocky Mountain region of North America [nebraska.pure.elsevier.com]

  Flaviviruses (Yellow Fever, Dengue, Dengue Hemorrhagic Fever, Japanese Encephalitis, West Nile Encephalitis, St. Louis Encephalitis, Tick-Borne Encephalitis). In: Mandell GL, Bennett JE, Dolin R, eds. [upmc-cbn.org]

  Symptoms manifest within 7–10 days and include fever, headache, partial paralysis, confusion, nausea and even coma. There is currently no established treatment.Half of all cases results in permanent neurological damage and 10-15% result in death. [en.wikipedia.org]

  Symptoms manifest within 7 10 days and include fever, headache, partial paralysis, confusion, nausea and even coma. [medicine.academic.ru]

• High Fever

  It may start (up to 3 weeks) after onset of the measles rash and present with high fever, convulsions, and coma. [medicine.academic.ru]

  I didn't remember much of the treatment due to the infection and high fevers I experienced. I do remember ice baths and a spinal tap or two. [inspire.com]

  Severe infections, however, occur with rapid onset and usually feature high fever, headache, and disorientation; they can include tremors, convulsions, paralysis, coma, and death. [mdedge.com]

  The 73-year-old woman grew weak and developed a high fever and meningitis before lapsing into delirium, becoming paralyzed and requiring a ventilator to breathe. She died about a month later. [pressherald.com]

  Clinical symptoms of Powassan virus begin with a high fever and progress to neurologic signs such as headache, vomiting, weakness, confusion, seizures and memory loss. [now.tufts.edu]

• Chills

  Other symptoms include chills, muscle aches and pains, headaches, and paralysis, Adalja says, noting that the disease can also cause encephalitis, which is an inflammation of the brain that can be deadly or lead to permanent disability, or meningitis, [yahoo.com]

  He went home from his job working for a plumber and napped for two hours, only to feel worse when he work up, with tremors, nausea and chills. A medical center gave him antibiotics because of his tick-bite history, Lane said. [capecodtimes.com]

  Fever, chills, aches, and fatigue are then the primary indicators, and not everyone who contracts Lyme may evidence these symptoms, particularly if they are hale, vigorous people who may tend not to show signs of illness, Mr. Telford said. [mvtimes.com]

• Rigor

  A 60-Year-Old Man with Fever, Rigors, and Sweats. New England Journal of Medicine 349 : 1168 – 1175. [cambridge.org]

• Constitutional Symptom

  The virus is transmitted by a tick bite, and constitutional symptoms followed by a range of neurological deficits, including altered consciousness, are typical features. [symptoma.com]

• Vomiting

  MalaCards based summary : Powassan Encephalitis, also known as powassan encephalitis virus infection, is related to encephalitis and lyme disease, and has symptoms including seizures, fever and vomiting. [malacards.org]

  Serum IgM PRNT 1:320 Steroids, IVIG Improved Patient 4 67 M DLBCL, in remission September 2014 Outdoors Y Y Vomiting, diarrhea Serum IgM PRNT 1:160 None Improved Patient 5 65 F Migraine headache June 2014 Tick bites Y N Vomiting Serum IgM PRNT 1:160 [academic.oup.com]

  Symptoms, including fever, headache, vomiting and memory loss, can start anytime from a week to a month after the tick bite. [necn.com]

  Symptoms include headache, fever, nausea, vomiting, stiff neck, and sleepiness, breathing distress, confusion, tremors, seizures, paralysis, and possible coma. Encephalitis and meningitis can occur – 10% of encephalitis cases result in death. [lymediseaseassociation.org]

  Signs and symptoms can include fever, headache, vomiting, weakness, confusion, seizures, and memory loss. Long-term neurologic problems may occur. Symptoms can begin anytime from one week to one month after the tick bite. [extension.umaine.edu]

• Nausea

  Symptoms manifest within 7–10 days and include fever, headache, partial paralysis, confusion, nausea and even coma. There is currently no established treatment.Half of all cases results in permanent neurological damage and 10-15% result in death. [en.wikipedia.org]

  The virus is antigenically related to the Far Eastern tick-borne encephalitis viruses. [4] Presentation Symptoms manifest within 7–10 days and include fever, headache, partial paralysis, confusion, nausea and even coma. [ipfs.io]

  Symptoms manifest within 7 10 days and include fever, headache, partial paralysis, confusion, nausea and even coma. [medicine.academic.ru]

  Symptoms include headache, fever, nausea, vomiting, stiff neck, and sleepiness, breathing distress, confusion, tremors, seizures, paralysis, and possible coma. Encephalitis and meningitis can occur – 10% of encephalitis cases result in death. [lymediseaseassociation.org]

• Hypertension

  […] bites Y N Vomiting Serum IgM PRNT 1:160 None Improved Patient 6 52 M None May 2014 Tick bites Y N None Serum IgM/IgG PRNT 1:160 b None Residual deficits Patient 7 49 M None May 2014 Tick bites Y N None Serum IgM PRNT Negative c None Death Patient 8 44 M Hypertension [academic.oup.com]

  Design/Methods: A case report of a 35-year-old woman who presented with worsening headaches, vomiting, hypertension, confusion, and fever. [neurology.org]

  Case 2 A 60-year old male who enjoys outdoor activity, with a history of colon cancer (treated with hemicolectomy and chemotherapy), diabetes mellitus and hypertension, presented to the emergency department with fevers, headaches and dizziness. [bmcresnotes.biomedcentral.com]

• Diplopia

  Patient 8 A 44-year-old man from New Hampshire presented with 3 days of headache, fatigue, diplopia, and a diffuse rash over his trunk and extremities (Table 1 ). [academic.oup.com]

• Headache

  Symptoms manifest within 7–10 days and include fever, headache, partial paralysis, confusion, nausea and even coma. There is currently no established treatment.Half of all cases results in permanent neurological damage and 10-15% result in death. [en.wikipedia.org]

  Survivors of POW: 50% have permanent neurologic problems – Headaches, muscle wasting, memory problems Supportive treatment is the only available treatment. [lymediseaseassociation.org]

  According to the Centers for Disease Control and Prevention, mild cases of arboviral encephalitis may present with only a slight fever and/or headache and body aches. [mdedge.com]

  The period between the tick bite and the appearance of symptoms (known as the incubation period) typically lasts between 1-5 weeks and a prodromal period of 1-2 days, comprised of nonspecific respiratory and constitutional complaints (fever, malaise, headaches [symptoma.com]

  The infection has symptom headache, has symptom fever, has symptom vomiting, has symptom stiff neck, has symptom sleepiness, has symptom breathing distress, has symptom tremors, has symptom confusion, has symptom seizures, has symptom paralysis, and has [malacards.org]

• Confusion

  Symptoms manifest within 7–10 days and include fever, headache, partial paralysis, confusion, nausea and even coma. There is currently no established treatment.Half of all cases results in permanent neurological damage and 10-15% result in death. [en.wikipedia.org]

  All but one patient developed encephalitis with acute onset of profound muscle weakness, confusion, and other severe neurologic signs. [ncbi.nlm.nih.gov]

  Soon after, severe deterioration characterized by ataxia, weakness, hemiplegia, ophthalmoplegia, confusion, somnolence and a severely altered level of consciousness, as well as seizures and other focal neurological deficits, are observed in the case of [symptoma.com]

  The infection has symptom headache, has symptom fever, has symptom vomiting, has symptom stiff neck, has symptom sleepiness, has symptom breathing distress, has symptom tremors, has symptom confusion, has symptom seizures, has symptom paralysis, and has [malacards.org]

• Seizure

  RESULTS: Case 1 was a 78 year old man who was presented with altered mental status and a 30 second generalized tonic-clonic seizure. He had no prior history of seizures. [neurology.org]

  MalaCards based summary : Powassan Encephalitis, also known as powassan encephalitis virus infection, is related to encephalitis and lyme disease, and has symptoms including seizures, fever and vomiting. [malacards.org]

  After the infant was treated for the seizures, he was released from the hospital, only to develop other complications 1 month later. [contagionlive.com]

  Soon after, severe deterioration characterized by ataxia, weakness, hemiplegia, ophthalmoplegia, confusion, somnolence and a severely altered level of consciousness, as well as seizures and other focal neurological deficits, are observed in the case of [symptoma.com]

  A 5-month-old infant living in eastern Connecticut was admitted to a hospital in November 2016 for evaluation and management of seizures that occurred a few days after onset of fever and vomiting. [ahcmedia.com]

• Altered Mental Status

  Symptomatic patients present 1 week to 1 month after infection with general symptoms of encephalitis, which include fever, headache, altered mental status, and seizures. [upmc-cbn.org]

  RESULTS: Case 1 was a 78 year old man who was presented with altered mental status and a 30 second generalized tonic-clonic seizure. He had no prior history of seizures. [neurology.org]

  Initial symptoms consist of fever and headache and, ominously, altered mental status. One-half have gastrointestinal symptoms and one-third have rash. Encephalitis, in some cases, may be delayed. [ahcmedia.com]

  If not treated, symptoms could extend to meningoencephalitis, which may include: seizures, aphasia, cranial nerve palsies, paresis and altered mental status. [en.wikipedia.org]

• Dizziness

  POWV infection can lead to encephalitis and varied neurologic presentations including headache, dizziness, hemiplegia, intraparenchymal hemorrhage and seizures. However, there are no known reports of status epilepticus secondary to POWV infection. [neurology.org]

  Patients with symptoms of encephalitis accompanied by a fever, and dizziness who live in tick infested areas should be tested for POW. Are there any tick vaccines? Currently there are no available tick vaccines in the US. [prahs.com]

  “But if there are neurological symptoms—weakness, dizziness, seizures—then it’s important to get to the doctor.” [time.com]

  The spectrum of infection varies from nonspecific prodrome of upper respiratory symptoms leading to varied neurological involvement such as headache, dizziness, weakness, and hemiplegia[ 8 ]. [bmcresnotes.biomedcentral.com]

  The journal of Clinical Infectious Diseases previously has reported that two Massachusetts men — one 82, the other 49 — died in 2015 and 2014 after contracting Powassan and demonstrating symptoms including dizziness, nausea, fever and headache. [capecodtimes.com]

Powassan encephalitis is a very rare cause of this type of infection and the clinical presentation is indistinguishable from other causes of viral encephalitis. However, its distinct geographical and epidemiological features are quite useful in including POWV in the differential diagnosis of encephalitis. For this reason, a detailed patient history is perhaps the essential part of the diagnostic workup. Firstly, Powassan encephalitis has a seasonal appearance, meaning that most cases are diagnosed from May through September [4] [6]. Secondly, a positive travel history to the endemic areas of the United States, Canada, or Russia (or if patients are residents of those areas) could significantly aid in suspecting Powassan virus as the causative agent. And thirdly, reports of a recent tick bite must direct the attention toward tick-borne encephalitis viruses (TEBV). Thus, a thorough physical examination is also a vital component of the workup, as it might reveal the site of the tick bite. Lumbar puncture examination is a must in the evaluation of the central nervous system (CNS) infections. Elevated protein levels are infrequently observed, but either lymphocytic or polymorphonuclear pleocytosis (between 200-700 WBCs/µL) is always seen in Powassan encephalitis [4] [6]. A definite diagnosis, however, can be made through the enzyme-linked immunoassay (ELISA) testing that detects specific immunoglobulin-M (IgM) antibodies to the Powassan virus in the cerebrospinal fluid (CSF), but these tests are only available in specialized laboratories and tertiary care centers [1] [2] [4] [6]. Imaging studies might also be of use in Powassan encephalitis, as magnetic resonance imaging (MRI) reveals can ischemic or demyelinating lesions in the basal ganglia, thalamus and the brainstem on T2/FLAIR images [4] [6].

• Cerebrospinal Fluid Abnormality

  Moderate pleocytosis and increased albumin can be found in the cerebrospinal fluid; abnormalities in the thalamus, cerebellum, and brainstem in MRI may be shown as well. [columbia-lyme.org]

1. Birge J, Sonnesyn S. Powassan Virus Encephalitis, Minnesota, USA. Emerg Infect Dis. 2012;18(10):1669-1671.
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;5:594.
3. Anderson JF, Armstrong PM. Prevalence and Genetic Characterization of Powassan Virus Strains Infecting Ixodes scapularis in Connecticut. Am J Trop Med Hyg. 2012;87(4):754-759.
4. Piantadosi A, Rubin DB, McQuillen DP, et al. Emerging Cases of Powassan Virus Encephalitis in New England: Clinical Presentation, Imaging, and Review of the Literature. Clin Infect Dis. 2016;62(6):707-713.
5. Tavakoli NP, Wang H, Dupuis M, et al. Fatal Case of Deer Tick Virus Encephalitis. N Engl J Med. 2009;360(20):2099-2107.
6. Mandell GL, Bennett JE, Dolin R. Mandel, Douglas and Bennett's Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, Pennsylvania: Churchill Livingstone; 2015.