Employees of the Santa Clara County Vector Control District will spray a foggy mist from trucks on streets in the Berryessa area of San Jose, said Noor Tietze, a scientific technical services manager for the district.
Previous eradication sprays for the Culex mosquitoes found to carry West Nile have been in South San Jose and extended west to Saratoga and Cupertino, Tietze said.
"We've never had a positive in that area of the county before," Tietze said. "It's entered a kind of new zone."
The pesticide fogging is scheduled for 11 p.m. Friday in the area, bounded by Landess Avenue on the north, Interstate Highway 680 to the west, Old Piedmont Road and foothills east and Berryessa Road on the south.
The fog-like spray, which is not toxic to humans or animals, is to be applied once to each street from containers loaded on pickup trucks late at night when most people are inside, Tietze
The effort against the insects infected with West Nile, which causes mild to severe flu-like symptoms such as fever and body aches, is the second this year within the county, after one done on July 11 in South San Jose, Tietze said.
There have been no reported infections of the virus in humans in the county this year, Tietze said.
Vector control detected the virus from many mosquitoes located in traps the agency placed in the Berryessa area and from dead birds reported by the public there, Tietze said.
The mosquitoes bite and infect the birds with the virus and then the insects feed on the still-alive birds, which become hosts for the spread of the virus to other mosquitoes, he said.