LA CROSSE ENCEPHALITIS
La Crosse encephalitis is a mosquito-borne, viral disease with the potential of infecting the central nervous system in humans, usually children under 15. The disease is named for La Crosse, Wisconsin, where it was first identified in 1963.
La Crosse encephalitis virus (LCEV) is an arbovirus that causes La Crosse encephalitis (LCE). Other important encephalitis arboviruses include the eastern equine encephalitis virus, St. Louis encephalitis virus, West Nile virus, and western equine encephalitis virus.
LCE is seen primarily in upper Midwestern, mid-Atlantic, and Southeastern states. LCEV is passed from one woodland mammal to another by the bite of a treehole mosquito. This mosquito breeds in treeholes (the area between the two main trunks of trees with two or more trunks) when rainwater collects there. It also breeds in man-made containers such as old tires, buckets, toys, cans, or anything that can hold water. The treehole mosquito is also found in deciduous forests or shaded areas; they do not fly more than 200 yards from where they were born. Unlike most other mosquitoes, treehole mosquitoes bite during the day.
When a mosquito ingests blood from an infected mammal, the virus replicates in the mosquito and moves to other locations in the mosquito’s body, including the salivary glands. When the mosquito takes its next meal on an uninfected mammal, it deposits a small drop of saliva at the bite, which acts as an anticoagulant. The saliva contains the virus, which enters the mammal, replicates, and becomes a source of virus for other mosquitoes that come for a meal. Once infected, the mosquito is infected for life (Figure 22).