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St. Louis encephalitis is a viral disease spread by infected mosquitoes. This disease can affect the central nervous system, causing severe complications and even death.

The Central Nervous System

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St. Louis encephalitis is caused by a virus with the same name. Mosquitoes are infected with this virus when they feed on birds. Infected mosquitoes can transmit the virus to humans and animals. St. Louis encephalitis is not spread from person to person.

Risk factors that increase your chance of getting St. Louis encephalitis include:

• Increased age
• Living in or visiting the southern, central, or western United States, especially during the summer and fall

St. Louis encephalitis can result in a wide range of symptoms or produce no symptoms at all. The disease can be mild, severe, or even fatal.

Symptoms usually appear 5-15 days after the bite of an infected mosquito and may include:

• Headache
• Fever
• Neck stiffness
• Rash
• Joint pain
• Stupor
• Disorientation
• Coma
• Tremors
• Convulsions (especially in infants)
• Paralysis

Your doctor will ask about your symptoms and medical history. A physical exam will be done. Blood tests will also be done to identify the virus.

There is no specific treatment for St. Louis encephalitis. Treatment will focus on managing your symptoms and complications, such as through supporting breathing and providing fluids.

There is no vaccine against St. Louis encephalitis. Prevention of this disease centers around controlling mosquitoes and avoiding mosquito bites. Steps you can take to avoid mosquitoes include:

• Stay inside between dusk and dark. This is when mosquitoes are most active.
• Wear long pants and long-sleeved shirts when outside.
• Spray exposed skin with an insect repellent that contains up to 35% diethyltoluamide (DEET).