St. Louis Encephalitis
Fact Sheet

What is St. Louis Encephalitis?
St. Louis Encephalitis is a mosquito-borne viral disease that causes inflammation of the brain.

How is St. Louis Encephalitis spread?
Occasionally, the house mosquito, Culex pipiens, may acquire the SLE virus from infected birds. It then can be transmitted to humans through a mosquito bite. There is no person-to- person transmission nor any transmission to or through pets.

Who gets St. Louis Encephalitis?
While the virus can affect anyone, it has its greatest impact on the very young and the very old because their immune systems are either in a state of development or decline. SLE can occur five to 15 days after the bite of an infected mosquito.

What are the symptoms of St. Louis Encephalitis?
Most people who are infected with SLE have no symptoms or only mild non-specific flu-like illness. However, in some individuals, especially the elderly, SLE can cause serious illness that affects the central nervous system. Symptoms often include a rapid onset of headache, high fever, stiff neck, disorientation and tremor. Coma, convulsions and paralysis may also occur.

How does someone know if they have St. Louis Encephalitis?
The diagnosis of SLE or any encephalitis is made by a physician. There is a blood test that will confirm the diagnosis of SLE, but this is rarely performed since there is no specific treatment for the disease.

How common is St. Louis Encephalitis?
SLE is a rare disease in the United States. There have been no cases reported in New Jersey since 1975. Nationwide, an average of 193 SLE cases are reported each year. Most of these cases are reported from southern states.

What is the season for St. Louis Encephalitis?
SLE virus transmission to birds B and to man during epidemics B is most likely from late summer through early fall. Mosquito populations tend to reach their annual peak during this period. While it is impossible to reliably predict epidemic activity, transmission to birds seems to increase when long periods of drought are broken by subsequent heavy rains.

Is there a vaccine for St. Louis Encephalitis?

Can St. Louis Encephalitis be treated?
Most individuals with SLE recover spontaneously without hospitalization. However, those developing more serious symptoms (disorientation, tremors, coma, or seizures) require hospitalization for supportive therapy (IV fluids and nutrition).

How can I reduce my risk of being bitten by mosquitoes?
Practice the following precautions:

What should I know about the mosquito that transmits SLE?
Culex pipiens are common in urban and suburban areas breeding in bird baths, clogged gutters, storm sewers, ditches, and other pools of stagnant water. They are attracted to light and readily enter buildings.

How can I find out about the mosquito control in my town?
In New Jersey, county mosquito control agencies have primary responsibility for the surveillance and control of mosquitoes. In addition to completing your own elimination of breeding sources around your home, you can contact your mosquito control agency which can provide additional mosquito control information and inform you of the status of mosquito surveillance and control in your town.

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