Symptoms of St. Louis Encephalitis

For Everyone

Key points

  • St. Louis encephalitis virus can result in febrile illness (fever) or neurologic disease, including meningitis or encephalitis.
  • If you think you or a family member might have St. Louis encephalitis, talk to your healthcare provider.
Woman with headache reads thermometer.

Symptoms

Most people infected with St. Louis encephalitis virus do not have symptoms. For people with symptoms, the time from mosquito bite to feeling sick (incubation period) ranges from 4 to 14 days.

Initial symptoms

Symptoms usually start abruptly, including:

  • Fever
  • Headache
  • Dizziness
  • Nausea
  • Generalized weakness

Symptoms typically get worse over a period of several days to a week. Some patients recover after this period.

Severe illness

Some people 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
  • Unsteadiness
  • Coma

Treatment

No medicines are available to treat St. Louis encephalitis. Rest, fluids, and over-the-counter pain medications may relieve some symptoms.

Outcomes and complications

St. Louis encephalitis can result in long-term disability. Among patients diagnosed with St. Louis encephalitis, 5 to 20% die. The risk of dying increases with age.

For Health Care Providers Clinical Signs and Symptoms of St. Louis Encephalitis

Risk factors

Illness is generally milder in children and young adults than in older adults.

Testing and diagnosis

If you think you or a family member might have St. Louis encephalitis, talk to your healthcare provider.

Healthcare providers diagnose St. Louis encephalitis 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 spread St. Louis encephalitis virus
  • Laboratory testing

Your healthcare provider can order tests to look for St. Louis encephalitis virus or other infections that can cause similar symptoms.

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Content Source:
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)