Review Topic
  • A 79-year-old man is brought to the emergency room after a trip to Texas in the summer. He was visiting extended family there where he sustained multiple mosquito bites. He reports having an intense headache and stiff neck. However, he does not exhibit signs of photophobia. He is not oriented to time or place and found to have a high-grade fever. There is no rash seen on examination. Laboratory evaluation reveals hyponatremia. (St. Louis encephalitis)
  • Introduction
    • flaviviruses
      • enveloped, linear, single-stranded, positive-sense virus RNA with icosahedral capsid
      • viruses
        • hepatitis C virus (HCV)
        • yellow fever virus
        • dengue virus
        • West Nile virus
        • Zika virus
        • St. Louis encephalitis virus
    • transmission
      • most are arboviruses and transmitted via mosquitos with the exception of HCV
      • HCV is transmitted via blood

Hepatitis C Virus
Yellow Fever Virus
Dengue Virus
West Nile Virus
Zika Virus St. Louis Encephalitis Virus
Clinical syndrome
  • Hepatitis
  • Hemorrhagic fever with hepatitis
  • Dengue hemorrhagic fever
  • Dengue shock syndrome
  • West Nile fever
  • Meningoencephalitis
  • Zika virus infection
  • Congenital microcephaly
  • St. Louis encephalitis
Differentiating factors
  • Jaundice
  • Right upper quadrant pain
  • Jaundice
  • Hemorrhage (epistaxis and mucosal bleeding)
  • Blanching erythematous maculopapular rash
  • Hemorrhage (tourniquet sign)
  • Non-pruritic papular rash
  • Acute flaccid paralysis with myoclonus
  • Pruritic rash
  • Microcephaly with intracranial calcifications
  • Flu-like illness without a rash
  • No photophobia
St. Louis Encephalitis
  • St Louis encephalitis virus
    • demographics
      • male > female
      • most cases in the eastern and central United States
    • risk factors
      • exposure to endemic areas
      • older age
    • transmission
      • via mosquitos from birds to humans
      • finches and sparrows are hosts
  • Presentation
    • flu-like illness
      • malaise, fever, cough, and sore throat
    • meningoencephalitis
      • does not present with photophobia
      • headaches, fever, nuchal rigidity, and confusion
    • seizures
    • SIADH
  • Studies
    • detection of antibodies to the arbovirus
    • detection of nucleic acid amplification from body fluids (CSF or blood)
    • CSF fluid
      • pleocytosis with a predominance of mononuclear cells
      • normal glucose
    • hyponatremia
  • Treatment
    • supportive care

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