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First Detection of West Nile Virus for 2023


First Detection of West Nile Virus for 2023 – A dead bird tests positive in San Mateo County

Burlingame, CA - July 24, 2023 - The San Mateo County Mosquito and Vector Control District reports a dead American Crow collected from the Redwood Shores area of Redwood City has tested positive for West Nile virus (WNV). This is the first detection of WNV activity in San Mateo County in 2023.

Certain birds, including American crows, common ravens, and American robins, may carry WNV. When a mosquito bites an infected bird, the mosquito can become infected. Infected mosquitoes can then pass the virus on to people or other animals that they bite. West Nile virus does not spread through coughing, sneezing, or person-to-person contact. Reports of dead birds are often the first sign of WNV in an area. Residents can report dead birds by phone at 877-WNV-BIRD (877-968-2473) or online at

When a dead bird tests positive for WNV, District staff set mosquito traps in the neighborhoods near where the dead bird was found to determine whether mosquitoes carrying WNV are in the area. District staff routinely inspect and treat mosquito breeding sources throughout the County to reduce the number of biting mosquitoes that could become infected and transmit WNV.

Residents can protect themselves from mosquito bites by using a mosquito repellent with an EPA-registered ingredient like DEET or picaridin when outside, particularly during dusk and dawn when the mosquitoes that spread WNV are most active. Residents can protect their community by dumping all standing water that can contribute to mosquito development. Residents noticing biting mosquitoes should report mosquito activity by calling the District at 650-344-8592 or visiting

For more information about West Nile virus and District services, call 650-344-8592 or visit The San Mateo County Mosquito and Vector Control District’s programs and services are funded through property taxes and benefit assessments and are provided to all residents in San Mateo County at no additional charge.

Contact: Rachel Curtis-Robles, PhD, Public Health Education and Outreach Officer


Phone: 650-344-8592


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