LaCrosse encephalitis: One of the main types of encephalitis caused by an arthropod-borne (carried by a mosquito, tick or another kind of arthropod) virus. The virus infects and inflames the brain. LAC encephalitis was first found in a 4-year-old in LaCrosse, Wisconsin in 1963. Since then, the virus has been identified in a number of Midwestern and Mid-Atlantic states. During an average year, about 75 cases of LAC encephalitis are reported to the CDC.
Most cases of LAC encephalitis occur in children under 16 years of age. LAC encephalitis initially presents as a nonspecific summertime illness with fever, headache, nausea, vomiting and lethargy. Severe disease occurs most commonly in children under the age of 16 and is characterized by seizures, coma, paralysis, and a variety of neurological sequelae after recovery. Death from LAC encephalitis occurs in less than 1% of cases.