St. Louis Encephalitis
St. Louis Encephalitis virus (SLEV) is a disease caused by a virus that is spread through mosquito bites. SLEV has been found from Canada to Argentina; however, the majority of human infections occur in the United States, particularly in the eastern and central states. In 2015, Maricopa County had its first SLEV outbreak that made 22 people sick. See current case counts in Maricopa County.
SLEV is spread primarily through mosquito bites. SLEV is spread to people primarily through the bite of infected Culex species mosquitoes. Culex mosquitoes are found in Maricopa County and other parts of Arizona and we do have mosquitoes infected with SLEV, although rare. These mosquitoes generally bite from evening to early morning so it is important to protect against mosquito bites whenever you are outside.
It takes 5-15 days for a person to develop symptoms after being bitten by a mosquito infected with SLEV.
Mild illness with fever in some people. Only 1 out of 100 people with SLEV will have symptoms. Individuals may develop sudden fever, headache, dizziness, nausea, and discomfort that lasts for several days to a week. The disease is generally milder in children than in older adults.
Severe symptoms in a few people. About 1 out of 150 people with SLEV will develop signs of neurologic illness, including stiff neck, confusion, dizziness, tremors, and unsteadiness, and in severe cases, coma may develop. Older individuals are more likely to develop encephalitis (swelling of the brain).
Individuals should see a healthcare provider if they develop the symptoms described above. The provider may order blood tests to look for SLEV or other similar viruses like WNV.
There are no specific treatment options. There is no specific medicine or vaccine available for SLEV infection. A doctor may recommend rest, fluids, and use of over-the-counter pain relievers can be used to reduce fever and relieve some symptoms.
Fight the Bite, Day and Night!
- Empty, drain or cover sources of standing water around your home to prevent mosquito breeding.
- When possible, wear long-sleeves, long pants, and socks when outdoors.
- When you go outdoors, use an EPA-registered insect repellent containing DEET.
- Insect repellents containing DEET are safe and effective during pregnancy.
- When using sunscreen, apply sunscreen first and then apply mosquito repellent.
- Do not apply repellent onto hands, eyes, mouth, and cuts or irritated skin.
- Dress your child in clothing that covers arms and legs.
- For children older than 2 months, use insect repellent on exposed skin. Adults should spray insect repellent on their hands and then apply to a child’s face.
- Cover crib, stroller, and baby carriers with mosquito netting.
- Products containing oil of lemon eucalyptus or para-menthane-diol should not be used on children younger than 3 years old.
Office of Epidemiology & Data Services
4041 N Central Avenue
Phoenix, AZ 85012
Phone 602-506-6767Fax 602-372-8935