St. Louis Encephalitis

Vector-Borne Disease
Public Health

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What you need to know

​​​​About St. Louis Encephalitis

St. Louis encephalitis virus (SLE) is an illness spread by the bite of an infected Culex mosquito. In Nebraska, Culex tarsalis is the primary vector mosquito. SLE can cause serious illness and death in people who are bitten by an infected mosquito. Anyone can get it, those who spend more time outdoors at dusk and dawn are at a higher risk of being bitten.

Culex mosquitoes are most active in Nebraska from May to October. They breed most often in areas of standing water. To reduce breeding in your yard, empty all standing water and remove containers, leaves and yard debris.

How is St. Louis Encephalitis spread to humans?

A mosquito becomes infected by feeding on a bird that has SLE. Once the mosquito has the virus it feeds on other birds, mammals or humans and transfers the virus. The majority of cases have historically been reported from areas in the eastern and central U.S. It is rarely reported in Nebraska but surveillance in Nebraska has showed that it is still circulating in mosquitoes in some areas of the state.

Because it is difficult to tell how many mosquitoes may be infected with a virus, it is important to prevent exposure to mosquitoes at all times.

Visit our Mosquito-borne Disease Prevention page​ to learn more about how you can prevent SLE.

Signs & Symptoms of St. Louis Encephalitis

Most people infected with St. Louis Encephalitis do not develop symptoms. For people with symptoms, the time from infected mosquito bite to feeling sick ranges from 4 to 14 days. 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 stiff neck, confusion, disorientation, dizziness, tremors, and unsteadiness. Coma can develop in severe cases.

The disease is generally milder in children and young adults than in older adults. Among patients diagnosed with SLE, 5 to 20% die. The risk of dying increases with age.

Mild signs and symptoms

  • Fever
  • Headache
  • Dizziness
  • Nausea
  • Fatigue

Severe signs and symptoms

  • Inflammation of the brain (encephalitis)
  • Confusion or disorientation
  • Occasional convulsions
  • Neck stiffness
  • Coma
  • Paralysis

St. Louis Encephalitis Treatment

There is no specific vaccine or treatment for St. Louis Encephalitis infection. Over-the-counter pain relievers can be used to reduce fever and 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.

If you think you or a family member might have St. Louis Encephalitis infection, talk with your health care provider.

For more information on St. Louis Encephalitis, contact your local health dep​artment or call the DHHS Office of Epidemiology at (402) 471-2937.

Additional Resources