Frequently Asked Questions
- What is St. Louis encephalitis?
- How do people get infected with St. Louis encephalitis?
- Where and when have most cases of St. Louis encephalitis disease occurred?
- Who is at risk for infection with St. Louis encephalitis?
- How soon do people get sick after getting bitten by an infected mosquito?
- What are the symptoms of St. Louis encephalitis disease?
- How is St. Louis encephalitis disease diagnosed?
- What is the treatment for St. Louis encephalitis disease?
- How can people reduce the chance of getting infected with St. Louis encephalitis?
- What should I do if I think a family member might have St. Louis encephalitis?
St. Louis encephalitis is a rare disease that is caused by a virus spread by infected mosquitoes. St. Louis encephalitis virus (SLEV) is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis).
SLEV is transmitted by the bite of an infected mosquito. SLEV is not transmitted directly from person to person.
Cases have been reported throughout the country, but periodic outbreaks and epidemics have primarily occurred in the Mississippi Valley and along the Gulf Coast. In temperate areas of the United States, SLEV disease cases occur primarily in the late summer or early fall. In southern states, cases can occur year round.
Anyone bitten by a mosquito in an area where the virus is circulating can get infected with SLEV. The risk is highest for persons who engage in outdoor work and recreational activities and those living in low-income areas. Elderly persons are at increased risk of severe disease if they are infected.
It takes 5 to 15 days after the bite of an infected mosquito to develop symptoms of SLEV disease.
Most people who are infected with SLEV have no symptoms or only mild non-specific flu-like illness. However, in some individuals, especially the elderly, SLEV can cause serious illness that affects the central nervous system. Symptoms often include fever, headache, stiff neck, disorientation, and altered level of consciousness. Coma, convulsions, and paralysis may also occur.
Diagnosis is based on tests of blood or spinal fluid. These tests typically look for antibodies that the body makes against the viral infection.
There is no specific treatment for SLEV disease. Antibiotics are not effective against viruses. Severe illnesses are treated by supportive therapy which may include hospitalization, respiratory support, IV fluids, and prevention of other infections.
Prevent mosquito bites. There is no vaccine or preventive drug.
- Use insect repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on exposed skin and/or clothing. The repellent/insecticide permethrin can be used on clothing to protect through several washes. Always follow the directions on the package.
- Wear long sleeves and pants when weather permits.
- Have secure, intact screens on windows and doors to keep mosquitoes out.
- Eliminate mosquito breeding sites by emptying standing water from flower pots, buckets, barrels, and other containers. Drill holes in tire swings so water drains out. Empty children’s wading pools and store on their side after use.
If you or anyone in your household has symptoms that are causing you concern, consult a healthcare provider for proper diagnosis.
- Page last reviewed: May 31, 2018
- Page last updated: January 13, 2010
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