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West Nile virus

Up Haemorrhagic fever Hendra virus Nipah West Nile virus


  • Flavivirus
  • Bird virus with mosquito vector (at least 49 species)
  • Closely related to St Louis encephalitis virus.
  • Also related to yellow fever and dengue viruses


  • Through most of North America
  • Africa
  • Southern Europe
  • Risk of severe encephalitis and of death higher in patients >60 years
  • Commonest transfusion related disease in USA

Clinical features

  • 80% asymptomatic
  • West Nile fever
    • primarily young adults
  • acute flaccid paralysis
    • middle aged patients (40-65)
    • similar clinical syndrome to acute poliomyelitis
    • respiratory failure in ~1/3. May be persistent
    • long term prognosis poor
  • encephalitis. May be severe
    • only ~30% discharged to independent living
    • >50% have neurological impairment at 1 year


  • no proven treatment
  • trials of ribavirin and specific immunoglobulin on-going



©Charles Gomersall, January, 2018 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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