West Nile virus detected in first Placer mosquitoes, but not yet Californians, this year

Placer is now the second county in the capital region with a confirmed detection of West Nile virus in mosquitoes.

A sample collected in the rural area west of Roseville, near Phillip Road, contained the first mosquitoes in the county to test positive for the disease, the Placer Mosquito and Vector Control District said in a news release Wednesday.

The announcement comes a week after the first positive test in a mosquito sample in Sacramento County. In the latest update Friday from the California Department of Public Health, the virus had been found in 128 mosquito samples statewide, up from 111 by the same point last summer. The number of dead birds with the virus sat at 17, a drop from 31 by the corresponding week last year, and no humans had yet tested positive for the disease in 2025.

Placer County vector control officials urged residents to wear insect repellent as a precaution against contracting West Nile, which is transmitted by mosquito bites and has no vaccine or cure for humans. Last year, California had 131 confirmed human cases of West Nile and 12 deaths due to the virus.

“With the ongoing warm temperatures this season, we anticipate we will see more West Nile virus activity after this initial detection,” Joel Buettner, the district manager for the Placer Mosquito and Vector Control District, said in a statement included in Wednesday’s news release.

“Our team is actively conducting surveillance and treatments to help reduce the risk of mosquito-borne disease transmission to our community,” he added.

Officials recommended that residents choose bug repellents endorsed by the Environmental Protection Agency and drain stagnant water to fend off the breeding of infected mosquitoes.

CDPH encourages residents to report dead birds by calling the department’s hotline at 877-968-2473. Residents can report issues on the district’s website, placermosquito.org.