Positive West Nile Virus Mosquitoes Found in Portions of Palo Alto and Mountain View

Targeted adult mosquito control treatment scheduled for Friday, September 17 in limited areas within Palo Alto and Mountain View

SANTA CLARA COUNTY, CALIF. The County of Santa Clara Vector Control District has confirmed the presence of West Nile virus (WNV) positive mosquitoes in areas of Palo Alto and Mountain View (ZIP Codes 94043, 94303, and 94306). Weather permitting, these areas will be treated to reduce adult mosquito populations with the use of truck-mounted equipment on Friday, September 17, starting around 10 p.m., and will conclude a few hours later.

Vector Control District has a dedicated surveillance program for diseases like West Nile virus, St. Louis encephalitis, and western equine encephalitis, which are transmitted through the bite of infected mosquitoes. The data collected through surveillance is used to predict locations that are more likely to have these disease-transmitting mosquitoes. When a WNV positive mosquito is detected, the District initiates an adult mosquito control treatment to reduce the mosquito population in the area, which reduces the risk of a WNV human infection.

The District has been conducting truck-mounted treatments regularly since 2003 to successfully reduce WNV-transmitting mosquito populations. The District will be adhering to requirements and recommendations from Santa Clara County Public Health for Coronavirus (COVID-19).

Distribution of door hangers notifying the affected neighborhoods of the scheduled mosquito treatment began Monday, September 13Additional notice is being sent directly to the public in the treatment ZIP codes through AlertSCC, and to those who subscribe to Nextdoor neighborhood networks and the District’s Mailchimp subscription. General notice is being provided on various social media platforms, including Facebook, Instagram, and Twitter (@SCCVCD), and a press release is also sent to local media news stations.

Vector Control staff will be available to answer any questions from the public, Monday – Friday, at the dedicated West Nile Virus Hotline at (408) 282-3114, from 7:30 a.m. to 4:30 p.m. Questions can also be submitted by email to [email protected]v.org.

The specific details of the operational areas are:

Treatment date:  Friday, September 17, around 10 p.m., for approximately three hours

Supervisorial Districts: District 5

Cities: Palo Alto and Mountain View

Centered at: West Middlefield Road and San Antonio Road

Bordered by:

  • North – Terminal Boulevard, East Meadow Drive, and Amphitheatre Parkway
  • East – Garcia Avenue, Amphitheatre Parkway, Sierra Vista Avenue, and Rengstorff Avenue
  • South – Alma Street and Old Middlefield Way
  • West – East Meadow Drive and Elwell Court

ZIP Codes affected: Parts of 94043, 94303, and 94306

Interactive map: https://arcg.is/1zSeDT

There is no need to relocate during the treatment. Mosquito treatments pose minimal risk to people, pets, animals, and the environment when applied by a licensed vector control professional following label instructions. Those who would like to take extra precautions can keep family and pets inside during the treatment, with windows and doors shut during the duration of the control treatment (approximately three hours). By sunrise, the insecticide will quickly break down with the sunlight. Since the District applies insecticides at the Ultra-Low Volume (ULV), individuals aren’t likely to breathe or touch anything that has enough insecticide on it to be harmful. Those with chemical sensitivities may want to consult their physicians for additional recommendations. All control materials utilized in our mosquito control program are approved by the Federal and State Environmental Protection Agencies and are widely used by Vector Control agencies throughout California.

For more information on the products used for this mosquito control treatment, including the safety data sheet, insecticide label, and a list of our most frequently asked questions, please visit our website at www.sccvector.org. For additional information on adulticides, visit the Centers for Disease Control and Prevention’s website at www.cdc.gov. For information on West Nile virus activity in California, please visit www.westnile.ca.gov.

Health Effects of West Nile Virus

Since the arrival of West Nile virus to California in 2003, 7,360 people across the State have contracted the disease; 339 of those cases were fatal. In 2020, there was one human WNV related fatality; 2015 was a record year for fatalities in the state with 55 deaths.

WNV infection does not cause symptoms in most people; however, for some individuals it can cause fever, headache, body aches and, in severe cases, significant neurological damage or death. Adults older than 50 years and individuals with certain chronic medical conditions such as diabetes, high blood pressure, cancer, and kidney disease are most at risk for serious complications. 

The District has a dedicated team that inspects locations throughout the county for mosquito breeding, searches for new sources, and eliminates any immature stages of mosquitoes. The public can also assist in preventing the spread of West Nile virus by taking the following prevention measures.

On your property:

  • Dump or drain standing water weekly. Mosquitoes need stagnant water to lay their eggs and spend three out of four life stages in water.
  • Drain, remove, or turn over anything that can hold water, such as flowerpots, planter bases, bird baths, toys, cans, rain gutters, pet dishes, buckets, and old tires. Fix leaky water faucets and sprinklers. For more information on water conservation and mosquito prevention, visit https://bit.ly/nowaternomosquitoes
  • Screens on doors and windows should be tight-fitting and in good condition.
  • Do not let your swimming pool water fall below the pump circulation area. Free mosquitofish placement can be requested online at www.sccvector.org for placement in neglected pools or ornamental ponds. For more information on our mosquitofish program, please visit www.sccvector.org/mosquitofish.

Outdoor Activities:

  • Limit outdoor activities during DUSK and DAWN to prevent mosquito bites. Those are the times when the mosquitoes that transmit WNV are most active. 
  • If you need to go outside in an area where mosquitoes are active
  • Dress in long sleeve shirts and long pants, preferably in light colors.
    • Apply insect repellent approved by the Environmental Protection Agency, following label instructions. For more information on mosquitoes, visit https://bit.ly/InfoMosquitoes.

Contact the County of Santa Clara Vector Control District if you are being bothered by mosquitoes or know of a potential mosquito-breeding source. For free assistance with mosquito control or other vectors, residents can contact the District office main line at (408) 918-4770 or fill out a service request online at www.sccvector.org.

Map of mosquito treatment area

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Media Contact: Beverly Perez, Vector Control District, (408) 210-5774


News Release


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