A Culex quinquefasciatus mosquito. Photo by James Gathany, USCDCP on Pixnio

The Fresno County Department of Public Health last week announced the first detected presence of St. Louis Encephalitis Virus (SLEV) in 2024, found by the Fresno County Mosquito Control Districts.

The mosquito-borne disease typically causes few symptoms if any, but in rare cases can cause severe illness mirroring that of meningitis/encephalitis (brain infection) and can lead to inflammation of the brain.

The most common symptoms of the illness are flu-like symptoms including fever and headache for 5 to 15 days following infection.

“This finding serves as a reminder that everyone should take this disease seriously and should take every precaution to protect themselves and their families from mosquito bites,”  said Dr. Rais Vohra, Fresno County Department of Public Health interim health officer. “The risk of disease due to SLEV usually increases at this time of year and is highest throughout the summer and early fall.”

SLEV is spread to humans through the bite of an infected mosquito and cannot be transmitted from person to person.

Mosquitoes become infected with the virus after biting infected birds.

SLEV can be found in mosquitoes in Southern California and the Central Valley and is transmitted in a similar manner as the more common West Nile Virus.

The Fresno County Department of Public Health recommends individuals contact their local mosquito control district to report standing water, such as neglected swimming pools or puddles, or to report mosquito problems.

The department also encourages residents to practice the “Three Ds”:

Deter – Apply insect repellent containing DEET, picaridin, oil of lemon eucalyptus or IR 3535. Repellents prevent mosquitoes from biting, but should not be used on children under two months of age.

Dawn and Dusk – Mosquitoes are most active during these times. The department recommends residents wear proper clothing and use repellent while outside during these times. It is also recommended that residents ensure doors and windows have tight-fitting screens with no tears or holes to prevent mosquito infestation.

Drain – Drain standing water sources when possible. Mosquitoes lay their eggs in standing water; residents can help curb mosquito infestation by emptying flowerpots, old car tires, buckets and other containers.

Residents are also encouraged to report dead birds to the California West Nile website or by calling toll-free 1-877-WNV-BIRD (968-2473).

Fresno County residents can also find their local mosquito abatement district here.