The Santa Clara County Vector Control District, which monitors the transmission of vector-borne diseases from insects, will be treating parts of Palo Alto and Mountain View with insecticide after recently detecting West Nile virus-positive mosquitoes in limited areas of the two cities.

Weather permitting, the district will use trucks to spray the impacted areas on Friday, Sept. 17, starting around 10 p.m., according to a county press release. The process should take three hours.

ZIP codes found with the infected mosquitoes include 94043, 94303 and 94306. According to the county, the area's borders are as follows:

• 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.

"There is no need to relocate during the treatment," the county said in the release. "Mosquito treatments pose minimal risk to people, pets, animals and the environment when applied by a licensed vector control professional following label instructions."

The district applies the insecticide at "ultra-low volume," which means a small amount of the chemical is used to treat a large area, according to the county press release. The county assures that people are unlikely "to breathe or touch anything that has enough insecticide on it to be harmful." People can choose to take extra precautions by keeping family and pets indoors during the three-hour treatment. Sunlight breaks down the insecticide, the county said.

The West Nile virus was first detected in California in 2003, and the county vector control district has regularly treated impacted areas with truck-mounted equipment ever since. With the insecticide, which is approved by the federal and state environmental protection agencies, the county is able to reduce the population of adult mosquitoes in the area.

Since the virus's arrival, 7,360 people in California have contracted the disease, and 339 of those cases were fatal. The record year for fatalities caused by infection was in 2015 with 55 deaths. In 2020, there was one recorded death.

In most cases, people do not feel symptoms, the county states.

"However, for some individuals it can cause fever, headache, body aches and, in severe cases, significant neurological damage or death," according to the release. "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 county provides some precautionary measures to avoid mosquito bites: limit outdoor activities from dusk to dawn, when mosquitoes are most active; dress in long-sleeved shirts and long pants, preferably in light colors, if going outside is a must; and wear insect repellent approved by the Environmental Protection Agency.

Residents also can install screens on doors and windows, dump or drain standing water on a weekly basis and fix leaky faucets and sprinklers. Mosquitoes thrive in stagnant water, according to the county.

The public can contact the vector control district's West Nile virus hotline Monday through Friday, from 7:30 a.m. to 4:30 p.m., at 408-282-3114. Questions also can be emailed to [email protected]

More information on how to prevent mosquitoes on a property and contact info can be found vector.sccgov.org.