The County of Santa Clara Vector Control District has confirmed the presence of West Nile virus-positive mosquitoes in a portion of Sunnyvale and Santa Clara (ZIP codes 94085, 94086, 94087 and 95051). Weather permitting, this area will be treated to reduce adult mosquito populations with the use of truck-mounted equipment on Thursday, Sept. 12, starting around 10 p.m. and concluding two to four hours later.
The district’s mosquito-management program largely focuses on preventing mosquitoes from reaching the adult biting stage by proactively targeting immature stages of mosquitoes found in standing water, using integrated pest management strategies. However, when a mosquito with West Nile virus (WNV) is detected, the district takes the added step of conducting adult-mosquito-control treatments.
It’s important for the district to conduct adult-mosquito-control treatments as quickly as possible upon finding a positive mosquito. Any delay would present an imminent threat to public health and safety, exposing the public to potential vector-borne illness or even death. The treatment reduces the mosquito population in the area, which decreases the risk of a WNV-human infection.
It is normal to see an increase in West Nile virus during the summer and early fall because mosquitoes thrive in warm weather. The district has a dedicated surveillance program to detect the presence of diseases like West Nile virus, St. Louis encephalitis and western equine encephalitis, all of 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.
The Santa Clara County Vector Control district has been conducting truck-mounted adult-mosquito-control treatments regularly since 2003 to successfully reduce WNV-transmitting mosquito populations.
Notice is being sent directly to the public in the adult-mosquito-control treatment ZIP codes through:
- Mailed postcards
- AlertSCC
- Emails to registered voters in specific precincts
General notice is provided on various social media platforms – including Facebook, Instagram, X (@SCCVCD) and Nextdoor – and to those subscribed to the district’s adult-mosquito-control treatment notifications.
Vector control staff are available to answer questions from the public from 7:30 a.m. to 3:30 p.m., Monday through Friday, on the agency’s dedicated West Nile Virus Hotline at (408) 282-3114. Questions can also be submitted by email to vectorinfo@cep.sccgov.org.
The details of the operation are:
Adult-mosquito-control treatment date: Thursday, Sept. 12, around 10 p.m., lasting two to four hours
Supervisorial districts: District 3 (parts of Sunnyvale) and 4 (Santa Clara)
Cities: Sunnyvale and Santa Clara
Centered at: Bramble Terrace and Ivory Palm Terrace in Sunnyvale
ZIP codes affected: 94085, 94086, 94087 and 95051
Interactive map: https://arcg.is/1fqjSq1
There is no need to relocate during the treatment. Adult-mosquito-control 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 members and pets inside during the treatment, with windows and doors shut. In the morning, the pesticide quickly breaks down when exposed to sunlight. Since the district applies pesticides at ultra-low volume (ULV), individuals aren’t likely to breathe or touch anything that has enough pesticide on it to be harmful. All pesticides used in our adult-mosquito-control program are approved by the U.S. Environmental Protection Agency for use in public areas and are widely used by vector control agencies throughout California.
For more information on the pesticides used for this adult-mosquito-control treatment, including the safety-data sheet, pesticide label and a list of frequently asked questions, visit our West Nile virus activity page. For additional information on pesticides, visit the Centers for Disease Control and Prevention’s webpage about insecticides that control mosquitoes. For information on West Nile virus activity in California, go to www.westnile.ca.gov.
Health Effects of West Nile Virus
Since West Nile virus arrived in California in 2003, more than 8,000 people across the state have contracted the disease; nearly 400 of those cases were fatal. In 2023, there were 18 human WNV-related deaths; 2015 was a record year for fatalities in the state with 53 deaths.
WNV infection does not cause symptoms in most people. However, for some individuals it can cause fever, headaches, body aches and, in severe cases, significant neurological damage or death. People with certain chronic medical conditions (such as diabetes, high blood pressure, cancer and kidney disease) and the elderly are most at risk for serious complications.
The public can assist in preventing the spread of West Nile virus by taking the following preventive measures.
On your property:
- Inspect for standing water on a weekly basis.
- Drain or turn over anything that can hold water, such as flowerpots, planter bases, pet dishes, buckets and old tires.
- Clean items like bird baths and pet bowls once a week to remove any mosquito eggs.
- Clear debris from rain gutters on a regular basis to allow water to flow.
- Properly screen rain barrels, cisterns and irrigation drains to prevent mosquito access.
- Fix leaky water faucets and broken sprinkler heads and avoid overwatering lawns and plants.
- Ensure window and door screens are in good condition with no holes or tears and are tight-fitting.
- Ensure swimming-pool water level is adequate for proper circulation and filtration.
- Free mosquitofish can be requested online for placement in neglected pools/spas, ornamental ponds, water troughs and other artificial bodies of water. For more information on our mosquitofish program, visit vector.santaclaracounty.gov/mosquitofish.
Outdoor activities:
- Limit outdoor activities during dusk and dawn – these are the times when the mosquitoes that transmit WNV are most active.
- If spending time outdoors, dress in long-sleeve shirts and long pants, preferably in light colors – mosquitoes are mostly attracted to dark colors.
- Apply insect repellent that contains DEET, IR3535 or oil of lemon eucalyptus, always following label instructions.
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 at (408) 918-4770 or submit an online service request.
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