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Fact Sheet: La Crosse Encephalitis


  • Frank encephalitis progressing to seizures, coma; majority of infections are subclinical or result in mild illness


  • La Crosse virus - California serogroup virus in the family Bunyaviridae


  • Approximately 70 cases reported per year


  • Case-fatality ratio <1%
  • Hospitalization for CNS infection
  • Neurological sequelae that resolve within several years


  • Short-term hospitalization to long-term care exceeding
  • $450,000
  • Social costs from adverse effects on IQ and school performance


  • Virus cycles in woodland habitats between the treehole mosquito (Aedes triseriatus) and vertebrate hosts (chipmunks, squirrels)
  • Virus survives winter in mosquito
  • Vector uses artificial containers (tires, buckets, etc.) in addition to treeholes


  • Children <16 years old: biological risk factor
  • Residence in woodland habitats environmental risk factor
  • Containers at residence environmental risk factor
  • Outdoor activities: behavioral risk factor


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


  • Traditional endemic foci in the great-Lakes states
  • Increased case incidence in mid-Atlantic states
  • Rural poor most affected


  • Multiple environmental, biological and social factors contributing to disease occurrence
  • Disease is considerably under-reported
  • No vaccine available


  • Prevention through proactive surveillance of enzootic cycle and education of residents in risk-reduction practices


  • Develop standardized national surveillance
  • Determine range and incidence of disease
  • Develop community education programs
  • Evaluate vector control strategies


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This page last reviewed November 7, 2005

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