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Fact Sheet:
La Crosse Encephalitis
CLINICAL FEATURES
- Frank encephalitis progressing to seizures, coma; majority of infections are subclinical
or result in mild illness
ETIOLOGIC AGENT
- La Crosse virus - California serogroup virus in the family
Bunyaviridae
INCIDENCE
- Approximately 70 cases reported per year
SEQUELAE
- Case-fatality ratio <1%
- Hospitalization for CNS infection
- Neurological sequelae that resolve within several years
COSTS
- Short-term hospitalization to long-term care exceeding
- $450,000
- Social costs from adverse effects on IQ and school performance
TRANSMISSION
- 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
RISK GROUPS
- 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
SURVEILLANCE
- Active case surveillance in collaboration with state and local health departments, and
mosquito control districts
TRENDS
- Traditional endemic foci in the great-Lakes states
- Increased case incidence in mid-Atlantic states
- Rural poor most affected
CHALLENGES
- Multiple environmental, biological and social factors contributing to disease occurrence
- Disease is considerably under-reported
- No vaccine available
OPPORTUNITIES
- Prevention through proactive surveillance of enzootic cycle and education of residents
in risk-reduction practices
RESEARCH PRIORITIES
- Develop standardized national surveillance
- Determine range and incidence of disease
- Develop community education programs
- Evaluate vector control strategies
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