The first case ever reported was in the early 1960’s in a Houston County, MN resident. The child died in a La Crosse, Wisconsin hospital, and the disease was subsequently named after this city.
La Crosse encephalitis is found in southeastern Minnesota, especially in counties along the Mississippi River. A 2012 Stearns County case represented the farthest north and west that La Crosse encephalitis virus has been reported to date in the United States.
The disease, which primarily affects children, is spread through the bite of infected Aedes triseriatus (Eastern Tree Hole) mosquitoes. Exposure to infected mosquitoes usually occurs in wooded or shaded areas, especially where water-holding containers (such as buckets, cans, or tires) provide good breeding habitat for the mosquito.
Similar to other arboviruses, most La Crosse encephalitis cases occur later in the summer (July through September) when infected vector populations are at their highest level.
In 2015, 1 case of La Crosse encephalitis was reported in Minnesota. The single case was a 44 year-old male, which is much older than the median case age from 1985-2015. Since 1985, 139 cases have been reported from 22 Minnesota counties, primarily in the southeastern part of the state.