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1. What Is St. Louis encephalitis (SLE)?

St. Louis encephalitis (SLE) is an inflammation of the brain. This viral infection is transmitted only by the bite of infective mosquitoes. SLE is transmitted by mosquitoes from the culex genus whose feeding activity is most intense during cooler temperatures at dusk, night, and at dawn. Mosquitoes become infected by feeding on birds infected with the St. Louis encephalitis virus.

When the virus enters the blood stream, it may localize in the brain causing inflammation of the brain cells and surrounding membranes. The brain tissue swells and can cause destruction of nerve cells, bleeding within the brain, and brain damage.

To contract SLE, you have to be bitten by an infected mosquito. Although the percentage of people who are bitten by an infected mosquito and actually get SLE is low, proper precautions should still taken in areas where culex genus mosquitoes live. Increased awareness and prevention methods are key to helping keep the number of SLE cases to a minimum.

2. What is being done in Memphis to prevent SLE?

SLE appears in epidemic form at intervals of approximately 10 years. The last outbreak in Memphis occurred in 1975, with 62 reported cases and 12 fatalities. To date, no cases have been reported in Memphis and Shelby County in over 20 years.

Since 1968, the Memphis and Shelby County Health Department's Mosquito Control Program has been actively involved in SLE surveillance by measuring antibodies to the virus in the blood of wild birds and chickens. These animals serve as a reservoir for the St. Louis encephalitis virus. Positive antibody testing serves as an early warning signal.

Although mosquito control is an important means of decreasing transmission of SLE to humans, personal protective measures are also important. Individuals can help by flushing any standing water in birdbaths, small wading pools, and pets' water bowls, and by adding fresh water daily. This will decrease the potential for mosquito breeding sites.

Although the majority of the cases reported during the outbreak were older adults, young children should not be considered low-risk, since they are a target population by being outdoors frequently.

3. What are the signs and symptoms of SLE?

The incubation period of SLE is between four and 21 days, with most cases being asymptomatic. The signs and symptoms of St. Louis encephalitis may become more severe as the disease progresses. Common symptoms include:

• Sudden fever
• Drowsiness
• Headache
• Vomiting
• Sensitivity to light
• Stiff neck

Symptoms that are serious enough to cause emergency medical attention may also include loss of consciousness, poor responsiveness, coma, seizures, muscle weakness or paralysis, sudden severe dementia, and memory loss (either short term or long term).

Remember, not all people with SLE develop the same symptoms, if any.

4. What are the causes?

A virus carried by an infected mosquito from the culex genus family causes St. Louis encephalitis. To contract SLE, you have to be bitten by an infected mosquito.

5. What are the risk factors of SLE?

Only a rare few mosquito bites lead to SLE. But if you know you've been bitten and experience symptoms of sudden fever, neurological changes, or other symptoms of SLE, go to the emergency room immediately.

6. What is the screening / diagnosis process?

A lumbar puncture test and cerebrospinal fluid (CSF) examination are required to detect SLE. Blood may be present in the CSF. Viral cultures of CSF or blood that reveal any type of virus will confirm the diagnosis. Serology tests are often the choice of a health care provider to provide evidence of viral infection. EEG test results that are abnormal may also signal SLE.

Additionally, a cranial MRI or a CT scan of the head may be used to determine the presence or absence of internal bleeding or edema.

7. What are some of the complications associated with SLE?

If left untreated, permanent neurological impairments, which may include loss of memory, speech difficulty or loss, diminished vision, hearing, and muscle control, can occur in people who survive severe cases of encephalitis.

8. What are the treatment options?

The goals of treatment are to provide supportive care and relieve symptoms. Antibiotics and/or antiviral medications are the standard treatment along with other medications needed to relieve symptoms. Treatment with antibiotics for several weeks usually cures the infection and prevents complications. It's important to take the full course of medications; for treatment to be most successful, do not discontinue taking these medication prematurely.

If the disease has progressed to a later stage, hospitalization may be necessary in some cases. Rest, nutrition, and plenty of fluids allows the body to fight the infection. Emotional support may also be helpful. If brain function is severely affected, physical therapy and speech therapy may be necessary after the acute illness is controlled.

9. What are some preventative measures I can take to prevent SLE?

You can decrease your chances of contracting St. Louis encephalitis by following some simple precautions:

• Mosquito-proof your yard by flushing any standing water in birdbaths where mosquitoes breed, twice weekly.
• Empty water from small wading pools and store indoors.
• If you have an ornamental pool, you can stock the pool with mosquito fish or treat the water with a larval control product.
• Provide fresh clean water in pet's bowls daily.
• Remove old tires, cans, non-working appliances or containers that will hold water.
• Repair leaky plumbing.
• Clean out rain gutters.
• Ensure proper screening around door and windows of your home.
• When outside, especially during cooler temperatures at dusk, night, and at dawn, wear light-colored clothing, long-sleeved shirts, and long pants. Try to avoid walking through low bushes and tall grass where there may standing water.
• Use insect repellents during the peak feeding times. Use EPA-approved products containing DEET with approximately 30% active ingredient. Be sure to follow label instructions carefully. Do not apply directly on the skin of children under the age of five.

10. Where can I find additional information about SLE?

For information on mosquitoes, contact the Memphis and Shelby County Health Department's Vector Control Section at (901) 324-5547. For St. Louis encephalitis information, contact the Epidemiology Section at (901) 576-7717.