St. Louis Encephalitis

St. Louis Encephalitis

Public Health Fact Sheet

What is St. Louis Encephalitis?
St. Louis Encephalitis, or SLE, is a serious viral disease that is transmitted to humans and animals through mosquito bites.

How is St. Louis Encephalitis spread?
The virus that causes SLE lives almost exclusively in the bloodstream of infected birds, and in the mosquitoes that bite those birds.  On rare occasions an infected bird will be bitten by a mosquito that bites both birds and people (and other animals), and in that rare situation, the virus can “spill over” into a person.  The risk of getting SLE, although small, rises during July through September.

How is SLE treated?
There is no specific treatment for SLE.   Medical care centers on treatment of symptoms and complications.

How is SLE prevented?
The best way to prevent SLE infection is to prevent mosquito bites as much as possible.  Use repellants.  Repellents containing 20-30% DEET work best.  Follow the label instructions carefully.  Do not use repellent on children younger than two years.  Limit outdoor activity in the evening when mosquitos are most active.  Maintain window and door screens. Eliminate all standing water that collects in birdbaths, boats, buckets, unused pools, roof gutters, etc.  Wear protective clothing such as long-sleeved shirts and pants.

Additional information is available on the CDC website at
Symptoms of St. Louis Encephalitis (SLE)

  • Abrupt onset of fever
  • Headache

  • Tiredness
  • Dizziness

February 2020