The campaign to kill mosquitoes carrying the West Nile virus came to Menlo Park's Allied Arts neighborhood and parts of downtown on Sunday evening.
The spraying "went exactly as planned," said Megan Caldwell, a spokesperson for the San Mateo County Mosquito and Vector Control District.
With near-ideal weather conditions -- a light wind and a temperature inversion -- two specially equipped trucks, each carrying a driver and a navigator, traversed the area at a slow and constant speed.
The trucks fogged the streets with the insecticide etofenprox, which loses its insect killing power in about 15 minutes, Ms. Caldwell said.
A third person on each team accompanied the truck in a separate vehicle to control traffic.
With the light wind and the insecticide airborne and in atomized form, even mosquitoes away from the streets are expected to have succumbed, Ms. Caldwell said.
The vector control district is conducting a day-after follow-up procedure of setting mosquito traps, and will be publishing the results, she said.
The fogging is a consequence of the vector control district's discovery of West Nile virus in two dead birds found on Thursday, July 30, one on Creek Drive and the other on Cambridge Avenue, Ms. Caldwell said. The district had a window of 24 to 72 hours to act to control the insects.
While West Nile is a disease that primarily affects birds, it is potentially dangerous to humans, horses and other animals. But transmission requires a bite from an infected mosquito. It is not contagious.