The Fresno County Department of Public Health (FCDPH) has confirmed its first positive case and death from St. Louis encephalitis (SLE) in Fresno County in 2022. This is one of several human cases of SLE detected in California this season.
SLE is a mosquito-borne disease caused by the St. Louis encephalitis virus (SLEV) and can produce inflammation of the brain. People contract SLE from the bite of an infected Culex mosquito. The mosquito becomes infected with the virus after biting a bird infected with SLEV. SLEV is not transmitted person to person.
Historically, SLEV has been found in the southern and Central Valley regions of California. However, since the introduction of West Nile Virus (WNV) into California in 2003, SLEV has been less commonly detected.
Symptoms usually start abruptly, with fever, headache, dizziness, nausea, and generalized weakness which typically get worse over a period of several days to a week. Some patients recover after this period. Most infections are mild or with no symptoms, however, others may develop signs of central nervous system infections, including stiff neck, confusion, disorientation, dizziness, tremors, and unsteadiness. Coma can develop in severe cases. There are no vaccines to prevent or medicines to treat SLE.