Saint Louis Encephalitis

Saint (St.) Louis Encephalitis virus (SLEV) is spread to people through the bite of infected mosquitoes. This virus is found in mosquitoes from Canada to Argentina although most human cases of disease have occurred in the United States. No cases have been reported in Connecticut. There is no vaccine to prevent transmission and no medicine to treat SLEV virus infection. The best way to prevent getting sick from SLEV is to prevent mosquito bites.

• CDC: About St. Louis Encephalitis
• Where Has St. Louis Encephalitis Been Found?

• Clinical Guidance
• National Surveillance Case Definition
• Connecticut Provider Reporting Information
• Connecticut Laboratory Reporting Information
• St. Louis Encephalitis testing at the State Public Health Laboratory
• State Public Health Laboratory Contacts – for additional information

The Connecticut Department of Public Health (DPH) added St. Louis Encephalitis to the reportable disease list in 2000. There have been no reported cases of SLE to the Connecticut Department of Public Health.

Connecticut Annual Infectious Diseases Statistics

• Connecticut Mosquito Management Program
• Workplace Safety - Mosquito-Borne Diseases

Updated 2/20/2026