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