St. Louis Encephalitis Virus

Some people may develop mild symptoms, including fever, headache, or nausea up to two weeks after being bitten.

Rarely, SLEV can cause more serious symptoms that affect the brain or central nervous system. These symptoms include stiff neck, confusion, and dizziness. Paralysis, coma, and sometimes death can result. Older adults, people with diabetes, and people with weakened immune systems are more likely to get very sick from SLEV.

• Apply EPA-registered insect repellent containing DEET, picaridin, IR3535, or oil of lemon eucalyptus on clothes and exposed skin before spending time outside. EPA-registered repellent is safe to use as directed and works to keep mosquitoes from biting you.
• Wear long sleeves and pants while outside when mosquitoes are active.
• Make sure doors and windows have tight-fitting screens to keep mosquitoes out of your home. If screens have tears or holes, fix or replace the screens to keep mosquitoes out.
• Mosquitoes that spread SLEV lay their eggs on standing water. You can prevent mosquitoes from breeding around your home by finding and removing sources of standing water in containers such as flower pots, tires, buckets, bird baths, and children's toys.
• Contact your local vector control agency if you notice more mosquitoes around your home than usual.

• CDPH SLEV webpage
• U.S. Centers for Disease Control and Prevention St. Louis Encephalitis webpage