St. Louis Encephalitis

St. Louis Encephalitis virus (SLEV) is a disease caused by a virus that is spread through mosquito bites.  SLEV has been found from Canada to Argentina; however, the majority of human infections occur in the United States, particularly in the eastern and central states. In 2015, Maricopa County had its first SLEV outbreak that made 22 people sick. See current case counts in Maricopa County.

  1. Transmission
  2. Signs & Symptoms
  3. Treatment
  4. Prevention

SLEV is spread primarily through mosquito bites. SLEV is spread to people primarily through the bite of infected Culex species mosquitoes. Culex mosquitoes are found in Maricopa County and other parts of Arizona and we do have mosquitoes infected with SLEV, although rare. These mosquitoes generally bite from evening to early morning so it is important to protect against mosquito bites whenever you are outside.