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West Nile Virus

General information

While human cases of West Nile virus are rare in San Mateo County, it’s a good idea to practice prevention and avoid mosquito bites. Although most people who become infected with the virus never develop any symptoms, some people may develop a more serious illness, such as meningitis or encephalitis. WNV is a seasonal epidemic in North America that flares up in the summer and continues into the fall. 

What you can do to help fight the bite and control West Nile Virus

  • Mosquitoes are most active at dusk and dawn so be sure to use insect repellent with DEET, and consider staying indoors or wear long sleeves and pants during these times.
  • Make sure you have good screens on your windows and doors to keep mosquitoes out.
  • Get rid of mosquito breeding areas by emptying standing water from anything that collects water (such as containers, flower pots, pet food and water dishes, swimming pool covers, buckets, etc.).
  • Report abandoned swimming pools by calling San Mateo County Mosquito & Vector Control District at (650) 344-8592.
  • Report a dead bird or squirrel by calling the WNV Dead Bird Hotline at 877-WNV-BIRD (877-968-2473) or click here to submit an online report. The hotline is staffed with live operators from 8:00 am - 4:30 pm Sunday through Friday.
  • Help get the word out to your family, friends, neighbors and community. Check out the educational materials below:

West Nile Virus in the U.S.

Since 1999, more than 30,000 people in the United States have been reported sick with West Nile Virus, which is spread by infected mosquitoes. In the U.S., there have been a total of nearly 700 human cases of West Nile Virus disease in 2013, and 26 deaths related to the virus.  This is the highest number of reported cases since West Nile Virus was first detected in 1999.  Most cases were reported from six states, including California.  For updated maps and statistics of WNV in the United States, visit the CDC’s information page.

West Nile Virus in California

For the latest state- and county-wide number of human and animal cases, visit

San Mateo County’s Mosquito Control Program

The San Mateo County Mosquito and Vector Control District is San Mateo County’s community-based mosquito control program. This program uses different methods to help control the risk of disease in San Mateo County, including surveillance, prevention and control of mosquito populations.

Vector Control does extra mosquito monitoring in neighborhoods where positive birds and squirrels are found.