St. Louis Encephalitis (SLEV) Confirmed in Yuba/ Sutter Area


Marysville, Ca.

The Sutter-Yuba Mosquito & Vector Control District reports it has received confirmation of the first positive mosquito for St. Louis encephalitis (SLEV) in our district. Mosquito samples recently collected in Plumas Lake, in Yuba County have tested positive for SLEV. The District is expanding both its surveillance system and mosquito control efforts in order to reduce the risk of infection.

SLEV is transmitted to humans through the bite of an infected Culex mosquito, the same mosquito that transmits West Nile virus. Like West Nile virus, SLEV is not transmitted person to person. SLEV has been found historically in many regions of California, such as the Central Valley and southern California, but has never been detected in our area before.

Most people bitten by a SLEV-infected mosquito will have few to no symptoms. Others will develop mild flu-like symptoms, including fever and headache from 5 to 15 days after being infected. Severe SLEV can result in serious symptoms that affect the central nervous system including stiff neck, disorientation, dizziness and tremors. Elderly people and those with weakened immune systems are more at risk for developing severe symptoms of the disease. For more about Saint Louis encephalitis virus, visit

It is very important to make sure to take simple precautions that reduce the risk of mosquito bites and becoming infected with mosquito-borne disease like West Nile virus and SLEV.
The 4 “D”s are an easy way to remember how to prevent mosquito bites:
D – DEET – use DEET, picaridin, oil of lemon eucalyptus or IR3535. These are the EPA approved mosquito repellents to prevent bites. Always follow package instructions for appropriate age and directions for use.
D – Dawn and Dusk – avoid going outdoors at dawn and dusk when the mosquitoes that carry WNV are most active. Wear long sleeves and pants if you have to be outdoors when mosquitoes are present.
D – Doors and windows – make sure that the screens on your doors and windows are not broken or torn.
D – Drain all standing water around the outside of your house – buckets, jar lids, tires and flower pot trays are some common places.


An aerial mosquito control application has been used for agricultural areas west of Yuba City on the evening of Tuesday, August 8, 2017. Spraying will be performed starting at sunset and lasting 2 to 3 hours. All treatments are dependent on appropriate weather conditions. Aircraft applications will be made with a yellow and blue stripe Air Tractor flying at approximately 300 feet in elevation. The spray program will be discontinued in the fall when there is a significant drop in the mosquito population and disease activity.

Over the mosquito season, the District will be using a combination of insecticides including Pyrethrins, Pyrethroids and Naled. Although these materials pose a low risk to human health, some people may prefer to avoid or minimize exposure by staying indoors, keeping their windows closed and turning off their window –mounted air conditioners, evaporative coolers and whole house fans when spraying is taking place in the immediate area. You can obtain additional information about spray operations by calling the District office at 674-5456 ext. 0 between the hours of 7 AM to 3:30 PM, Monday thru Friday.

West Nile virus is transmitted to humans through the bite of an infected mosquito. Residents are strongly encouraged to limit outdoor activities during peak mosquito feeding times at dawn and dusk. When outside and mosquitoes are biting, wear long sleeves and long pants and apply a mosquito repellent. Keep mosquitoes outside of your home by making sure that door and window screens are in good repair.

The spraying covering Plumas Lake and Olivehurst have been ongoing for the last 4 weeks.

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