For the first time in 37 years, Wisconsin health officials have reported a confirmed human St. Louis Encephalitis (SLE) case. The patient is a resident of Dane County. The last case in Wisconsin was reported in 1981.

Wisconsin map/National Atlas of the United States
Wisconsin map/National Atlas of the United States

St. Louis Encephalitis virus (SLEV) is transmitted from birds to man and other mammals by infected mosquitoes (mainly some Culex species). SLE is found throughout the United States, but most often along the Gulf of Mexico, especially Florida.

Most persons infected with SLEV have no apparent illness. Initial symptoms of those who become ill include fever, headache, nausea, vomiting, and tiredness. Severe neuroinvasive disease (often involving encephalitis, an inflammation of the brain) occurs more commonly in older adults. In rare cases, long-term disability or death can result.

SLEV is not transmitted person-to-person. SLEV is rare in Wisconsin, with only six human cases reported between 1964 and 2018 and no major outbreaks ever reported in the state.

There is no specific treatment for SLEV other than to treat symptoms.