St. Louis Encephalitis
by Amy Scholten, MPH
St. Louis encephalitis is an infection from a mosquito. It can range from mild to life-threatening.
St. Louis encephalitis is caused by a virus. It is spread to humans from the bite of an infected mosquito. The virus is not spread from person to person.
Things that may raise the risk of St. Louis encephalitis are:
St. Louis encephalitis can cause a wide range of symptoms. However, sometimes there are no symptoms. The disease can be mild, severe, or even fatal.
Symptoms may be:
The doctor will ask about your symptoms and health history. A physical exam will be done. Blood tests are usually used to diagnose the virus.
There is no specific treatment for St. Louis encephalitis. Treatment depends on how severe the disease is. The goal is to manage symptoms and problems. Depending on the symptoms, options may be:
To reduce the risk of St. Louis encephalitis:
Centers for Disease Control and Prevention
National Institute of Allergy and Infectious Diseases
Alberta Ministry of Health
Curren EJ, Lindsey NP, et al. St. Louis encephalitis virus disease in the United States, 2003-2017. Am J Trop Med Hyg. 2018;99(4):1074-1079.
Measurement of St. Louis encephalitis virus antibody. EBSCO DynaMed website. Available at: https://www.dynamed.com/lab-monograph/measurement-of-st-louis-encephalitis-virus-antibody. Accessed April 2, 2021.
Mosquito avoidance. EBSCO DynaMed website. Available at: https://www.dynamed.com/prevention/mosquito-avoidance. Accessed April 2, 2021.
Saint Louis encephalitis fact sheet. Centers for Disease Control and Prevention website. Available at:
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Accessed April 2, 2021.
Last reviewed December 2020 by EBSCO Medical Review Board David L. Horn, MD, FACP
Last Updated: 4/2/2021
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