The Alameda County Mosquito Abatement District announced Thursday via its Twitter account new cases of West Nile virus in the area.
Officials report a squirrel in Livermore and three crows in the Fremont/Newark area have tested positive for the virus.
Alameda County now has five birds and a squirrel that have tested positive for West Nile, the district said.
The squirrel was found in a neighborhood east of the Livermore airport, officials said. The area is just south of where officials found a earlier this month.
"There is indication in Livermore of West Nile virus activity occurring, and it wouldn't be confined to one address,"said Chindi Peavey, Alameda County Mosquito Abatement District manager.
Peavey said the district has stepped up its treatment and inspection of the area.
"We are not getting a large number of mosquitoes there," she said. "We tested pools of mosquitoes and haven't had any positive (results) of West Nile."
Residents who are experiencing mosquito bites are encouraged to call the district at 510-783-7744.
"They should call us because there may be hidden sources that we didn't know about," Peavey said.
Residents who come across dead birds, squirrels or any other deceased animals are asked to report it to the state hotline number at 877-WNV-BIRD.
National figures reflect a 40 percent increase in West Nile virus cases since last week.
Those stats indicate the number of cases may rival the record years of 2002 and 2003, the Associated Press reported.
For more information about mosquitoes and West Nile Virus visit mosquitoes.org.