News Release
Los Angeles County Public Health Logo

313 N. Figueroa Street, Room 806  |  Los Angeles, CA 90012  |  (213) 288-8144  |

twitter logo instagram logo facebook logo youtube logo Spotify logo

For Immediate Release:

August 10, 2018

Saint Louis Encephalitis Virus Found in Los Angeles County Mosquitoes

LOS ANGELES – The Los Angeles County West Vector Control District in collaboration with the Los Angeles County Department of Public Health have confirmed that a mosquito sample collected in Playa Vista is the first positive for the St. Louis Encephalitis virus (SLEV) in Los Angeles County for 2018. Residents should take steps to prevent mosquito bites and eliminate mosquito breeding sites on their properties.

SLEV is a native arbovirus in the same virus family as West Nile virus (Flaviviridae). SLEV is similar to West Nile virus (WNV) in that both viruses require birds as reservoirs to maintain the virus in nature. Environmental detections of SLEV have reduced significantly over the years since the introduction of West Nile virus. It is believed that WNV caused a cross-immunity in birds and the virtual disappearance of SLEV. SLEV first reappeared in Riverside County in 2015 and has also been found in Los Angeles, Riverside, Kern, San Bernardino, Orange County, and Ventura County in 2016 and 2017. Although no human SLEV cases have been confirmed since 1997 in Los Angeles County, human cases have occurred elsewhere in California.

WNV and SLEV are transmitted to people via the bite of an infected mosquito. Mosquitoes are infected when they feed on birds carrying the virus. Most individuals infected with WNV or SLEV will not experience any illness. Others will have flu-like symptoms, such as fever, headache and body aches.

In severe cases, SLEV and WNV can affect the central nervous system resulting in meningitis and/or encephalitis and can result in death and long-term disability. Persons over the age of 50 years or individuals with lowered immune systems are at greater risk of experiencing severe symptoms when infected. Anyone with symptoms should contact their health care provider. The best way to prevent getting infected is to prevent mosquito bites.

Decrease your risk of infection:

1. USE MOSQUITO REPELLENTS: Mosquito repellents containing DEET, picaridin, IR3535, and oil of lemon eucalyptus are the longest lasting and most effective. Repellents keep the mosquitoes from biting you.

2. DAWN AND DUSK: Mosquitoes that carry SLEV primarily bite in the early morning and evening so it is important to wear repellent at this time.

3. MOSQUITO PROOF YOUR HOME: Make sure that your doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.

4. DRAIN STANDING WATER: Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property, including flowerpots, old car tires, rain gutters and pet bowls. Ensure that swimming pools, spas, and ponds are properly maintained.

5. POOLS AND SPAS: Clean and maintain swimming pools, spas, and drain water from pool covers.

Dead birds should be reported to the California Department of Public Health at (877) 968-2473.

Please contact the Los Angeles County West Vector Control District at (310) 915-7370 to report mosquito problems, request mosquitofish, and report neglected pools or standing water where mosquitoes breed. Visit the Los Angeles County West Vector Control District at to obtain more information, submit service requests and see weekly updates on West Nile virus.

More information and resources can be found at: