Updated: 6/6/2018

West Nile Virus

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Snapshot
  • A 60-year-old woman is brought into the emergency room for confusion and flaccid paralysis. Her family reveals that she recently made a trip to Asia and arrived home just a few days ago. On physical exam she is febrile and is not oriented to person, place, or time. She has hyperreflexia and flaccid paralysis of both legs. Cerebrospinal fluid analysis reveals elevated lymphocytes, normal protein, and normal glucose. Further analysis reveals immunoglobulin M to the suspected virus.  
Introduction
  • Classification
    • West Nile virus
      • an enveloped, positive single-stranded RNA virus
      • a flavivirus
    • transmission
      • mosquitoes
  • Epidemiology
    • demographics
      • more severe in the elderly
      • more common in the young
    • risk factors
      • mosquito bites
  • Pathogenesis
    • mosquito’s saliva transmits the virus to human blood
    • virus then replicates in dendritic cells and spreads via lymphatics and bloodstream
    • in some patients, the virus can invade the central nervous system and cause meningoencephalitis
      • paralysis occurs when neurons are damaged in the anterior horn of the spinal cord
  • Associated conditions
    • West Nile fever
    • meningoencephalitis
  • Prognosis
    • most infections are asymptomatic
    • when symptomatic, the disease may progress to meningitis or encephalitis in < 1% of those infected
Presentation
  • Symptoms
    • West Nile fever
      • headache
      • myalgias
      • nausea and vomiting
      • may develop a rash
    • meningoencephalitis
      • confusion
      • coma
      • acute headache
      • photophobia
      • nausea and vomiting
  • Physical exam
    • West Nile fever
      • non-pruritic papular rash
        • on trunk and extremities
      • lymphadenopathy
      • conjunctivitis
    • meningoencephalitis
      • acute flaccid paralysis
      • myoclonus
      • cerebellar ataxia
      • seizures
      • sensory is intact
Imaging
  • Magnetic resonance imaging (MRI)
    • indication
      • meningoencephalitis
    • findings
      • increased signal intensity in affected areas
Studies
  • Labs
    • immunoglobulin M (IgM) enzyme-linked immunosorbent assay
      • serum
      • cerebrospinal fluid
    • cerebrospinal fluid
      • normal glucose
      • ↑ or normal protein
      • ↑ lymphocytes
  • Making the diagnosis
    • based on clinical presentation and laboratory studies
Differential
  • Dengue fever
    • distinguishing factor
      • characterized by mucosal bleeding, hemorrhage, and abdominal pain
Treatment
  • Management approach
    • mainstay is supportive care
  • Conservative
    • supportive care
      • indication
        • all patients
      • modalities
        • fluids
        • pain management
        • mechanical ventilation
Complications
  • Rhabdomyolysis
  • Guillain-Barré syndrome

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