Updated: 8/20/2022

West Nile Virus

Review Topic
  • A 34-year-old man presents to a local urgent care after returning from a trip to Africa. He has endured multiple mosquito bites throughout his 2-week safari trip. He states that, like several members of his tour group, he has had a 3-day history of fever, non-itchy rash, and myalgias. One tour group member, however, developed seizures and confusion. This patient is scared that he may also develop severe symptoms like seizures. On physical exam, he has conjunctival injection and a papular rash on his trunk and legs. Given his age and current symptoms, his physician reassures him that it is highly unlikely but to watch out for any signs of meningoencephalitis.
  • Classification
    • West Nile virus
      • an enveloped positive single-stranded RNA flavivirus
    • transmission
      • Culex 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
  • 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
  • Magnetic resonance imaging (MRI)
    • indication
      • meningoencephalitis
    • findings
      • increased signal intensity in affected areas
  • 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
  • Dengue fever
    • distinguishing factor
      • characterized by mucosal bleeding, hemorrhage, and abdominal pain
  • Management approach
    • mainstay is supportive care
  • Conservative
    • supportive care
      • indication
        • all patients
      • modalities
        • fluids
        • pain management
        • mechanical ventilation
  • Rhabdomyolysis
  • Guillain-Barré syndrome

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