St. Louis Encephalitis

Saint Louis encephalitis virus is transmitted to humans from the bite of an infected Culex species mosquito. It is a flavivirus, a single-stranded positive-sense RNA virus, which is closely related to the Japanese encephalitis, Powassan, and West Nile virus. Most cases occur in the eastern and central United States during the summer and early fall. Most cases are asymptomatic or present with flu-like symptoms such as fatigue, headaches, nausea, vomiting, and body aches. Most patients will spontaneously recover without progression to encephalitis. Severe, invasive disease resulting in encephalitis is unusual and is more common in older adults. Encephalitis or inflammation of the brain and meninges presents as dizziness, agitation, confusion, tremors, or coma following the flu-like prodrome. For patients with encephalitis, the overall case fatality rate is 5% to 15%. There is no specific treatment for St. Louis encephalitis beyond supportive care. Antivirals have not been shown to alter symptoms. There is no vaccine available, so the focus is on the prevention of mosquito bites.