Key points
- St. Louis encephalitis virus can result in febrile illness or neurologic disease, including meningitis or encephalitis.
- If you think you or a family member might have St. Louis encephalitis, talk with your health care provider.
- There is no specific treatment for St. Louis encephalitis.
- Rest, fluids, and pain medications may relieve symptoms.
Symptoms
Most people infected with St. Louis encephalitis virus do not have symptoms. For people with symptoms, the time from infected mosquito bite to feeling sick (incubation period) ranges from 4 to 14 days. The disease is generally milder in children and young adults than in older adults.
- Symptoms usually start abruptly, with fever, headache, dizziness, nausea, and generalized weakness.
- They typically get worse over a period of several days to a week.
- Some patients recover after this period.
- Others develop signs of central nervous system infections, including inflammation of the brain (encephalitis) or the membranes around the brain and spinal cord (meningitis).
- Symptoms can include stiff neck, confusion, disorientation, dizziness, tremors, and unsteadiness.
- Coma can develop in severe cases.
- Among patients diagnosed with St. Louis encephalitis, 5 to 20% die.
- The risk of dying increases with age.
Diagnosis
If you think you or a family member might have St. Louis encephalitis, talk with your healthcare provider.
- Healthcare providers diagnose St. Louis encephalitis virus infection based on:
- Signs and symptoms.
- History of living in or traveling to an area where St. Louis encephalitis virus is known to circulate.
- History of possible exposure to the mosquitoes that can carry St. Louis encephalitis virus.
- Laboratory testing of blood or spinal fluid.
- Your healthcare provider can order tests to look for St. Louis encephalitis virus infection and other infections that can cause similar symptoms.
To learn more about testing, visit our Healthcare Providers page.
Treatment
- There are no vaccines to prevent or medications to treat St. Louis encephalitis. Antibiotics are not effective against viruses, including St. Louis encephalitis virus.
- Rest, fluids, and over-the-counter pain medications may relieve some symptoms.
- In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.
To learn more about treatment, visit our Healthcare Providers page.