First West Nile virus cases confirmed in Los Angeles County for 2025

Four people have been hospitalized with West Nile virus infections in Los Angeles County, marking the first confirmed human cases of the mosquito-borne disease for the 2025 season, health officials announced.

The cases were reported from late July through late August and involve residents of the Antelope Valley, San Fernando Valley and central Los Angeles. All four individuals are recovering.

“The first human cases of West Nile virus are an important reminder that we all need to take steps to prevent mosquito bites and mosquito breeding,” said Dr. Muntu Davis, Los Angeles County health officer. “Mosquitos thrive in hot weather, increasing the risk of bites and mosquito-borne diseases.”

West Nile virus is transmitted through the bite of infected mosquitoes and can cause fever, headache, nausea and body aches. In severe cases, it may lead to meningitis, encephalitis, paralysis or death. Older adults and people with chronic health conditions are especially at risk for complications.

The Los Angeles County Department of Public Health reports an average of 56 West Nile Virus cases annually, though actual infections are likely much higher since many people experience mild or no symptoms and are never tested.

About 75% of reported cases involve severe disease, with a 10% fatality rate among those patients.

To reduce the risk of infection, officials urge residents to use EPA-approved insect repellent, wear long sleeves and pants when outdoors, and ensure window and door screens are intact. Standing water in items like flowerpots, buckets, pet bowls and gutters should be emptied regularly to prevent mosquito breeding.

“Detecting West Nile virus in our district is a reminder that this virus has been present in California — and right here in our community — for over 20 years,” said Brenna Bates-Grubb of the Antelope Valley Mosquito and Vector Control District. “It only takes a small amount of water for mosquitoes to breed.”

More information is available at publichealth.lacounty.gov.