Saint Louis Encephalitis

A close-up, anterior view of a female Culex tarsalis mosquito, as it was about to begin feeding, after having landed on the skin of what would become its human host

Saint Louis encephalitis (SLE) is a viral disease spread to people by the bite of an infected mosquito. Most people infected with SLE virus 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. There are no vaccines to prevent nor medications to treat SLE. Care is based on symptoms. You can reduce your risk of infection with SLE virus by using insect repellent, wearing long-sleeved shirts and long pants, and taking steps to control mosquitoes indoors and outdoors.