Mosquitos infected with West Nile Virus (WNV) have been found in parts of Mountain View and Palo Alto, according to a recent Santa Clara County advisory statement.

The Santa Clara County Vector Control District plans to use a spray treatment to target the affected areas on Thursday, Sept. 14, starting at 10 p.m. The roll out will occur through the use of truck-mounted equipment, and the treatment will take about two to four hours to complete.

“Any delay in the application would present an imminent threat to public health and safety, exposing the public to potential vector-borne injury, or even death,” the district said, adding that since 2003, when WNV was first detected in California, more than 7,000 people have contracted the disease from mosquitos with 400 fatal cases.

Typically, the district focuses on early prevention efforts that targets the immature stages of mosquitoes found in standing water. But the presence of WNV has prompted the district to ramp up its control treatments and go after adult mosquitos to reduce the risk of WNV transmission to humans, according to the statement.

It is not necessary to relocate during the control treatment, although people can close their windows and keep pets inside if they are worried about pesticides. The treatment is applied by a licensed vector-control professional and approved by the Environmental Protection Agency; it also breaks down quickly when exposed to sunlight, the statement said.

The treatment area will include the ZIP codes 94301, 94303, 94304, 94306 and 94040.