West Nile virus (WNV) is a mosquito-borne virus that spreads to people through the bite of an infected female mosquito. Mosquitoes become infected when they feed on infected birds. It can make people, horses, and birds sick and even cause death.

There is no cure and no vaccine for people but there is a vaccine for horses. Fortunately, most people infected with WNV do not feel sick. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. The best way to prevent WNV is to protect yourself from mosquito bites.

How are we responding to the risk of West Nile virus transmission to people?

Placer Mosquito’s staff is working to prevent or stop the spread of West Nile virus in Placer County. Our surveillance program monitors mosquitoes throughout the county for disease and reports the detections here. We educate residents on how they can help limit West Nile virus and we make treatments to target both larval and adult mosquitoes. We rely on Placer County residents to report dead bird sightings through the California Department of Public Health’s West Nile Virus Call Center online at westnile.ca.gov or by calling 1-877-WNV-BIRD to help us monitor dead birds for West Nile virus.

Current West Nile Virus Activity

July 11, 2024 – The Placer Mosquito and Vector Control District confirmed the first mosquito sample to test positive for West Nile virus in the county for 2024. The mosquitoes were collected in Sheridan, a rural area in northwest Placer County.

California West Nile Virus Reporting