Rare Human Cases Of Mosquito-Borne Encephalitis Virus On Rise In CA

LONG BEACH, CA — The first documented human case of St. Louis Encephalitis virus in Long Beach since 1984 was discovered on Friday, according to health officials.

As of Nov. 9, this is the 14th case of St. Louis Encephalitis discovered in the state this year, according to the California West Nile Virus Website. There have been about five times as many infected mosquitoes found statewide this year than in all of 2022. Starting last year, the Golden State saw a dramatic spike in human cases of the virus, according to health officials. In 2022, California had 16 human cases compared to the five previous years when the state averaged less than five human cases a year.

The spike in human cases comes as the state endures skyrocketing mosquito populations. This year, there have already been more than 700 infected mosquitoes found compared to 152 in all of 2022, according to statewide health officials.

“The first confirmation of (St. Louis Encephalitis virus) in Long Beach should serve as a reminder that we need to protect ourselves against mosquitoes,” said Health Officer, Dr. Anissa Davis. “The Health Department encourages everyone to continue reporting issues regarding mosquito control in their area.”

Mosquito-borne diseases have been on the rise as the mosquito population exploded this season. Los Angeles County reported two locally transmitted cases of dengue fever less than a month ago. One of those cases was recorded in Long Beach.

According to the California Department of Public Health, human cases of St. Louis Encephalitis virus are not common in the Golden State and fewer than 10 cases have been reported per year in 1990. Mosquitoes infected with St. Louis Encephalitis virus are most commonly found in the Central Valley and some areas of Southern California, CDPH said.

According to Long Beach health officials, the risk of local exposure remains low and officials are taking extra steps to prevent any further spread of the virus that causes St. Louis Encephalitis virus. The person who has been infected was hospitalized but is now recovering at home and no other suspected cases have been identified.

Encephalitis is spread to people by the bites of culex mosquitoes and is in the same virus family as the West Nile virus with similar symptoms. The virus is not spread from person to person and most infected people will not experience symptoms.

Most people who experience symptoms typically have mild fevers, headaches or nausea. Severe cases of SLEV can affect the brain and nervous system, causing stiff neck, confusion, dizziness and sometimes death.

There are currently no vaccines or medicines that treat or prevent encephalitis, but healthcare providers recommend recovery treatments such as staying hydrated, resting and taking medication for pain and fever.

"We are working diligently with healthcare providers to educate the community to prevent more cases of (St. Louis Encephalitis virus),” said Mayor Rex Richardson. “Mosquito control is a shared responsibility and residents must take an active role in reducing the threat of mosquito-borne illnesses in their neighborhoods.”

Mosquitoes that transmit the virus are most active at dusk and dawn, health officials said. Residents were encouraged to eliminate any standing water in or around their homes to prevent the breeding of additional infected mosquitoes.