St. Louis Encephalitis virus (SLEV) is a mosquito-borne virus that can cause inflammation of the brain, known as encephalitis. It primarily affects humans and horses, with symptoms ranging from mild flu-like signs to severe neurological issues. The virus is mainly transmitted through the bite of infected Culex mosquitoes. SLEV is prevalent in the Americas, particularly in the United States. While many infections are asymptomatic, severe cases can lead to complications such as seizures, coma, or even death. There is no specific treatment for SLEV, making prevention through mosquito control and personal protection essential.