Residents don't need to relocate during the spraying, since the treatment poses minimal risk to people, pets, animals and the environment, according to Santa Clara County.

This is not the first time this year the West Nile virus has been detected in mosquitoes in Santa Clara County. The county detected cases and treated areas of Santa Clara and Sunnyvale at the end of August.

Environmental nonprofit Healthy Alternatives to Pesticides takes legal action against Santa Clara County over pesticide spraying.

Mosquitoes found in Campbell, Los Gatos, Monte Sereno and San Jose tested positive for West Nile Virus, county officials warned Monday.