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Fact Sheet: Arboviral Encephalitis


  • Aseptic meningitis or encephalitis. Many cases have only fever with headache
  • Can progress to focal paralysis, intractable seizures, coma and death


  • Several alpha-, flavi- and bunya- viruses; chiefly, St. Louis encephalitis (SLE), western equine encephalitis (WEE), Venezuelan equine encephalitis (VEE), eastern equine encephalitis (EEE), La Crosse virus and other California serogroup viruses


  • Varies with occurrence and intensity of epidemic transmission; usually 150-3,000 cases/year


  • Neurologic sequelae in 30% of EEE cases; 10% of SLE cases
  • Case fatality rate of 30% in EEE cases; 5% of SLE cases


  • $150 million - includes estimated cost of vector control and surveillance activities


  • Chiefly mosquito-borne


  • SLE - elderly; low income areas
  • La Crosse encephalitis - children
  • WEE - rural residents of the West


  • Active surveillance in collaboration with state and local health departments, and mosquito control districts


  • Changes in lifestyle, emphasizing outdoor activity and "natural" residential locations increase risk of exposure


  • Infrequent but unpredictable epidemics
  • Surveillance methods not adequately sensitive or not utilized
  • Develop more effective surveillance, prevention and control strategies
  • Control methods impractical
  • Control methods not fully evaluated
  • Prevention tools limited
  • No human vaccines available
  • Treatment not always effective
  • Knowledge of geographic distribution incomplete


  • Evaluate natural cycle indices of virus activity and develop surveillance systems that predict epidemic transmission
  • Develop and evaluate public health education and intervention strategies


  • Develop predictive, standardized national surveillance system
  • Improve techniques to survey natural transmission cycles
  • Improve laboratory diagnostic assays
  • Evaluate vector control modalities
  • Evaluate infection prevention approaches
  • Improved diagnostic tests
  • Develop and evaluate vaccines


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This page last reviewed February 9, 2009

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National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
Division of Vector-Borne Diseases (DVBD)
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Fort Collins, Colorado 80522

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