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First Discovery of St. Louis Encephalitis in Mosquitoes in Lancaster, CA

Lancaster, CA – The Antelope Valley Mosquito and Vector Control District (AVMVCD) has detected St. Louis encephalitis virus (SLEV) in a mosquito sample from 8th Street East and Avenue J-6. St. 

Louis encephalitis, similar to West Nile virus, is a viral infection spread to people through the bite of an infected mosquito. Initial symptoms of those who become ill include fever, headache, nausea, vomiting, and tiredness.

Severe neuro-invasive disease (often involving encephalitis, an inflammation of the brain) can occur more commonly in older adults. In rare cases, long-term disability or death can result. There are no vaccines to prevent SLEV nor medications to treat SLEV. Medical care after contracting an SLE virus infection is supportive and is based on symptoms. St. Louis encephalitis reemerged in the state of California in 2015 after being undetected for 12 years.

Photo : CDC

It has since been increasing throughout the state, and was detected in the Antelope Valley in Sentinel chickens during both the 2016 and 2017 mosquito season. This 2019 detection of SLEV is the first detection in a mosquito sample in the Antelope Valley. It is also the first detection in Los Angeles County as a whole for the 2019 mosquito season.

AVMVCD personnel have increased mosquito surveillance in the area and will continue to place traps in order to monitor the mosquito population.

There was also a mosquito sample that tested positive for West Nile virus (WNV) near 11th Street East and Avenue K-8. That brings the total to 6 WNV positives in the Antelope Valley this year. Although District Vector Control Technicians treat breeding sources daily for the purpose of mosquito control, the public also plays a critical role in helping to control the mosquito population. The District urges residents to do their part to protect themselves from mosquito bites by following these recommendations:  Wear EPA registered ingredients such as DEET, picaridin, oil of lemon eucalyptus, or IR3535 to exposed skin (as directed by the product label).  Wear long sleeve shirts, long pants, socks and shoes when mosquitoes are most active.  Be sure window and door screens are in good repair to prevent mosquitoes from entering your home.  Inspect yards for standing water sources and drain water that may have collected under potted plants, in bird baths, discarded tires, and any other items that could collect water.  Check your rain gutters and lawn drains to make sure they aren’t holding water and debris.  Ensure pools are cleaned and maintained or completely dry. To stay up-to-date on any mosquito related information check out our website at, Facebook page (, and follow us on Twitter and Instagram @AVMosquito. For any further questions or services please feel free to contact the Antelope Valley Mosquito & Vector Control District by phone (661-942-2917)

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