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First human case of St. Louis encephalitis recorded in Kern County

California is experiencing high mosquito activity this year due to the winter storms, and Kern County mosquitos have tested positive for both West Nile and St. Louis encephalitis.
Posted: 6:14 PM, Jul 10, 2023
Updated: 2023-07-10 21:30:41-04
mosquitos (FILE)

BAKERSFIELD, Calif. (KERO) — According to Kern County Public Health, there have been 10 mosquito samples collected in the county this year that have tested positive for West Nile Virus, and 8 with St. Louis Encephalitis. Now, with the county's first confirmed case of SLE in a human, a health alert has been issued.

"Mosquitos can cause infections that can cause severe illness in people. They can cause death, so this is an unfortunate reminder that St. Louis encephalitis is here in our community," said Division Director of Health Services for the Kern County Public Health Department Kimberly Hernandez.

According to Hernandez, some symptoms that are associated with SLE are headaches, fever, fatigue, body aches, nausea, and in severe cases, swelling of the brain, although she adds that in most cases, the virus will not be severe and that there are ways to help prevent transmission by preventing mosquito bites.

"Avoiding standing water, reducing standing water, cleaning those areas where standing water might collect," said Hernandez. "Because, again, that's where mosquitos breed and where you tend to start the development of those infestations."

The Kern Mosquito and Vector Control District acknowledges that the heavy rain Kern County saw this past winter is playing a huge factor in the busy mosquito season, according to Mark Dery, the district's scientific program director.

"With all the water that we had it's provided ample breeding areas for mosquitos, and we are doing our best to cover it all, but we really need all residents of the area to make sure they are checking their backyards and front yards and dumping any water that they find," said Dery.

Dery says only one certain breed of mosquitos transmit the West Nile Virus and St. Louis encephalitis.

"It's not all mosquitos. It is the most abundant ones in our areas in the genus Culex," said Dery.

According to Hernandez, anyone diagnosed with SLE with severe symptoms could wind up hospitalized, because there is no vaccine available.

"There isn't a specific treatment for it either, so most of it, if you have to be hospitalized, is things like IV fluids, supportive care, and managing your symptoms," said Hernandez.


St. Louis encephalitis is not a new disease. According to the Centers for Disease Control and Prevention, episodic outbreaks of the virus have been recorded in U.S. cities since at least the 1930s.

The CDC says that 2022 saw the highest number of reported cases of SLE since 2003. In 2003, there were 49 reported cases. In 2022, there were 32.

From 2003 to 2022, the age group that saw the most SLE infections overall was those aged 70 and above, comprising a full quarter of reported cases.

During that same time period, a total of 283 cases were reported, with 190 people being hospitalized. 18 died of complications arising from SLE infection.

Arizona recorded the highest number of SLE infections between 2003 and 2022 overall with 85, followed by California with 43.