LaCrosse Encephalitis Facts & Information:

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