Mosquitoes test positive for West Nile virus in Palo Alto and Los Altos

The Santa Clara County Vector Control District plans to treat a section of Palo Alto and Los Altos, highlighted above in green, to reduce the mosquito population on Oct. 20, 2022. Mosquitoes found in the area recently tested positive for West Nile virus. Courtesy Santa Clara County Vector Control District.

Mosquitoes have tested positive for West Nile virus in a small area of Palo Alto and Los Altos, the Santa Clara County Vector Control District said on Wednesday.

The areas, which include ZIP codes 94304, 94306 and 94022 will be treated on Thursday starting at 10 p.m. to reduce adult mosquito populations, weather permitting. Truck-mounted equipment will apply the treatment over the area for approximately four hours.

A notice is being sent directly to the public in the treatment ZIP codes through AlertSCC and to those who subscribe to Nextdoor neighborhood networks. A general notice is being provided on various social media platforms — including Facebook, Instagram and Twitter — and to those subscribed to the district’s mosquito treatment notifications.

West Nile virus arrived in California in 2003. More than 7,000 people statewide have contracted the disease; nearly 400 of those cases were fatal. In 2021, there were 12 human West Nile virus-related deaths; 2015 was a record year for fatalities in the state with 55 deaths, the district said.

West Nile virus infection doesn’t cause symptoms in most people, but for some individuals it can cause fever, headache, 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 older adults are most at risk for serious complications.

The district’s usual mosquito-management program largely focuses on preventing mosquitoes from reaching the adult biting stage by targeting immature stages of mosquitoes found in standing water. When a mosquito with West Nile virus is detected, the district conducts adult mosquito-control treatment to reduce the mosquito population in the area, which decreases the risk of a West Nile virus-human infection, the district said.

It’s normal to see an increase in West Nile virus during the summer and early fall because mosquitoes thrive in warm weather. Although mosquitoes need water at each stage of life, they are still able to thrive during the drought conditions the state and county are currently experiencing, the district said.

Residents in the affected area do not need to relocate during the treatment. The treatments pose minimal risk to people, pets, animals and the environment when applied by a licensed vector control professional following label instructions, the district said.

Anyone wanting to take extra precautions can keep family members and pets inside during the treatment hours, with windows and doors shut. Once the sun rises, the insecticide quickly breaks down when exposed to sunlight.

The district applies the insecticides at ultra-low volume so that people and pets aren’t likely to breathe or touch anything that has enough insecticide on it to be harmful. Anyone with chemical sensitivities might want to consult their physicians for additional recommendations, the district said.

The treatment will be centered at Wilkie Way and West Charleston Road bordered by the following areas:

• North — St. Claire Drive, Chimalus Drive, Lambert Avenue, El Carmelo Avenue and Loma Verde Avenue.

• East — Middlefield Road, Christine Drive, Grove Avenue, Sutherland Drive, Park Boulevard, Waverly Street and Cowper Street.

• South — San Antonio Road, Showers Drive, Sherwood Avenue, McGregor Way, Miranda Avenue and Roble Ridge Road.

• West — Los Altos Square, Paso Robles Avenue, Santa Rita Avenue, Laverne Way and Alta Mesa Cemetery.

The treatment materials are approved by governmental environmental protection agencies and are widely used by vector control agencies throughout California, according to the district.

The district said the public can help prevent the spread of West Nile virus by taking the following prevention measures:

On 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 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 at sccvector.org for placement in neglected pools/spas, ornamental ponds, water troughs and other artificial bodies of water. For more information on our mosquitofish program, visit sccvector.org/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.

Residents can contact the Santa Clara County Vector Control District if they 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’s main line at 408- 918-4770 or submit an online service request.

Vector Control staff is available to answer any questions from the public on the dedicated West Nile Virus Hotline at 408-282-3114, from 7:30 a.m. to 4 p.m., Monday through Friday. Questions can also be submitted by email to vectorinfo@cep.sccgov.org.

More information on the products used for the adult mosquito-control treatment, including the safety data sheet, insecticide label and a list of the most frequently asked questions, can be found at sccvector.org. Additional information on mosquito control is available at the adulticides webpage of the Centers for Disease Control and Prevention. For information on West Nile virus activity in California, go to westnile.ca.gov.