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Current West Nile Virus Information for San Mateo County

San Mateo County Mosquito and Vector Control District was notified by San Mateo County Health of a possible case of West Nile virus (WNV) in September 2021. Upon notification, the District collected adult mosquitoes for WNV testing by deploying mosquito traps in a targeted area of the County. Mosquitoes were tested for WNV, and all tested mosquitoes were negative. No elevated risk for WNV has been detected in the County in 2021 during the District’s standard WNV surveillance.

WNV is primarily a disease of birds. However, humans, horses, and other animals can become infected with WNV if bitten by an infected mosquito. WNV cannot be spread from person to person. In addition to surveillance for WNV, the District controls mosquitoes in their immature stages through an integrated pest management (IPM) program. The District’s vector control technicians routinely inspect standing water where mosquitoes develop, and treat mosquito breeding sources throughout the County.

As residents plan for travel during the winter holiday season, SMCMVCD reminds residents that mosquito-borne diseases can be transmitted year round in warmer climates.  If you are travelling someplace warm for the holidays, remember to pack an EPA-registered mosquito repellent to prevent mosquito bites and disease transmission.


The California state West Nile virus hotline closed for the season to live calls on October 15. However, residents can still make an online report at District staff will continue to collect and test suitable birds through the winter months.


During winter months when West Nile virus activity is low, this page will not be updated.  Please refer to the California Department of Public Health's West Nile Virus website for up-to-date information, or contact our office at 650-344-8592.


Date last reviewed: December 8, 2021

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