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West Nile Virus Information & Resources

West Nile Virus

The San Mateo County Mosquito and Vector Control District is responding to the presence of West Nile virus (WNV) in our region. Spreading through the bite of an infected mosquito, WNV can cause disease in humans, horses, and birds, making people sick and sometimes causing death. Most people who contract WNV have mild or no symptoms and will recover quickly. While the risk of serious illness from WNV is low for most people, older adults and immunocompromised people are at higher risk for severe disease. West Nile virus does not spread through coughing, sneezing, or person-to-person contact.

West Nile virus was detected in one dead bird collected in the Redwood Shores area of Redwood City. Vector Control installed traps to collect mosquitoes, but no mosquitoes from that area tested positive for WNV. To date no mosquitoes elsewhere in the county have tested positive for WNV.

In response to WNV, County Health’s role is to investigate confirmed or suspected cases in residents to determine the source of the infection and report the information to Vector Control.

Santa Clara County has announced a human case of WNV in an adult resident who was infected elsewhere. Santa Clara County’s Vector Control has detected WNV in local mosquitoes and has begun spraying.

San Mateo County residents can report biting mosquitoes by calling Vector Control at (650) 344-8592 or submitting a service request online at:

Residents can report dead birds to the state hotline at (877) 968-2473 or submit a report online at:

People can protect themselves from mosquito bites with these steps: 

  • Wear long-sleeved shirts and long pants, especially from dusk to dawn when mosquitoes are most active 
  • Use insect repellent. EPA-registered repellents are safe and effective. EPA-registered repellents typically include one of the following ingredients: DEET, picaridin, oil of lemon eucalyptus, IR3535, or permethrin (for pre-treating clothing) 
  • Once a week, dump items that contain water, such as tires, buckets, plant saucers, toys, kiddie pools, birdbaths, or trash containers. Mosquitoes need water to grow from egg to adult. Removing water means reducing mosquito populations. 
  • Check and repair broken screens on windows and doors to keep mosquitoes out of your house
  • While the risk of being infected with West Nile virus in San Mateo County is currently low, residents are reminded that many other parts of the state have higher risk. Use insect repellent while spending time outdoors while traveling

Questions about WNV should be directed to the San Mateo County Mosquito and Vector Control District.