"August and September are critical months for West Nile virus," said Steve Schutz, scientific program manager for the Contra Costa Mosquito and Vector Control District. "The mosquito species that can transmit West Nile virus are plentiful enough that they start feeding more on people as well as birds. Sometimes, there just aren't enough birds to go around."
West Nile virus can cause flu-like symptoms and is often spread to humans after a mosquito bites a person after biting an infected bird, according to the Contra Costa County Mosquito and Vector Control District.
District officials said 42 people in Contra Costa County have been infected with the virus since 2005. In 2006, two people died from the disease.
According to the district, recent data shows that most human cases of the virus go unreported or undiagnosed.
So far this year, no human cases have been reported in the county but a total of four groups of mosquitoes and 31 dead birds tested positive for the virus.
Seven dead American crows found in Contra Costa County during the past week tested positive for the virus. Three were found in Brentwood, two in Pittsburg, one in Discovery Bay and one in Walnut Creek, according to the district.
The public is encouraged to keep mosquitoes at bay by dumping or draining standing water, wearing mosquito repellant and avoiding being outside when mosquitoes are most likely to be present; typically at dawn or dusk.
County residents may report any mosquito problems to the district by calling (925) 771-6195.