A dead bird found on Grant Road near El Camino Hospital - infected by a mosquito carrying West Nile virus - prompted four crews from the Santa Clara County Vector Control District Tuesday night to fog a large of area of Mountain View and portions of Los Altos, an operation that extended into the early hours of Wednesday morning.
Portions of Mountain View and Los Altos have seen an increase in mosquito activity lately, and West Nile virus was found in some adult mosquitoes less than a mile away, near the intersection of Cuesta Drive and Miramonte Road, according to Santa Clara County Vector Control District spokesman Bob Kaufman.
The fogging began around 11 p.m. and lasted for about four hours in an area roughly bordered by Villa Street and Escuela Avenue on the north; Clark Avenue, Verano Drive, North Gordon Way, South El Monte Avenue and Campbell Avenue on the west; state Highway 85 and Sun Mor Avenue on the east; and Covington Road and Levin Avenue on the south.
Kaufman said the substance sprayed - Zenivex - is only toxic to mosquitoes and was sprayed at less than an ounce per acre.
About a quarter of the area targeted Tuesday night was previously fogged during an operation on Aug. 9, Kaufman said.
He said that said after a fogging, adult mosquito populations usually decrease by about 80 percent, which, in turn, helps decrease the odds of West Nile virus spreading to humans.
"If there's less mosquitoes flying around ... that's going to reduce the chances," Kaufman said.
He said the vector control district keeps a close eye on larvae sites and monitors buckled curbs and streets where water can pool and provide a mosquito breeding ground.
Residents are asked to drain any standing water around their homes, and properly maintain their swimming pools.
Kaufman said that although West Nile virus activity is on the rise nationwide this year, Santa Clara County appears to be seeing only average activity.
Last year, the district conducted four sprayings. Last night's fogging was the second of the year. Kaufman is not yet sure if the District will need to fog again.
District officials said the ultra-low concentration sprayings do not pose safety hazards for residents or the environment.
-Bay City News contributed to this article.