Arboviral Encephalitis

CLINICAL FEATURES

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

AETIOLOGIC AGENT

  • 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

INCIDENCE

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

SEQUELAE

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

COSTS

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

TRANSMISSION

  • Chiefly mosquito-borne

RISK GROUPS

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

SURVEILLANCE

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

TRENDS

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

CHALLENGES

  • 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

OPPORTUNITIES

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

RESEARCH PRIORITIES

  • 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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