SAN JOSE -- A murder of crows blackened the spotless white examination table -- a dozen gape-beaked birds, each in its own zip-locked body bag, tagged and ready for testing one recent day.
Their deaths weren't much of a mystery: Vector control workers immediately identified the primary suspect that knocked the crows from their perches, a prediction that proved true when the first results arrived minutes later. Crimson streaks that appeared on test strips confirmed suspicions that West Nile virus had struck again.
"We're seeing more than in all the other years," said Mike Stephenson, the disease surveillance specialist with Santa Clara County Vector Control who swabbed the beaks of the crows to check for the deadly virus, which is carried by mosquitoes and also poses tremendous risk to humans.
"We've had other busy years, but not like this."
As of July 3, the county logged 286 infected birds; that's nearly 60 percent of the positives counted statewide and more than three times the number found in all of 2013. At this time last year, positive hits could be counted on one hand. Once the birds' infection is confirmed, workers then seek to zero in on infected mosquitoes, which are more difficult to track.
Local and state officials can't pinpoint with certainty a reason for the high numbers, but they are worried about what the dead birds portend for the county's residents. The California Department of Public Health cited conditions such early warm temperatures and a lack of rainfall as possible boosters.
"That certainly seems to be one of the factors," county vector manager Russ Parman said of the drought. He said that while it seems counterintuitive -- less water should mean less mosquito breeding -- it actually has the opposite effect.
"Birds and mosquitoes are in closer contact because they come together at the same watering holes," Parman said.
Whatever the reasons, Santa Clara County stands out among neighbors. San Mateo County found its first infected bloodsucker in years, which resulted in a mosquito fogging last month. Contra Costa County has seen 10 dead birds and one infected mosquito sample and fogged twice this year. In Alameda County, which hasn't fogged in 15 years, five infected birds have been found and no mosquitoes.
By contrast, Santa Clara County is on track to easily surpass last year's record 13 foggings, with the 10th taking place July 3.
The trigger to bring out the chemicals is a positive virus hit in a mosquito -- the only way to kill the adults is through the spraying -- and they've been getting those hits this year, with 16 so far. Sacramento County has had the most statewide: 76. But at this time last year, there were none in Santa Clara County.
The increased fogging doesn't sit well with some residents, who have shown up to county meetings to voice their concerns about truck-mounted misters spewing poison through their neighborhoods in the dead of night.
"I'd like to know who is advising the county that spraying is worth it," said Jennifer Schmid, a nurse from Sunnyvale. "This stuff is so toxic. Where's the cost-benefit risk analysis?"
That "stuff" used in fogging operations is pyrethroid. Parman said the pesticide has been studied extensively and is a less toxic, synthetic version of the chrysanthemum-based pyrethrin commonly found in flea shampoos. He also said that in 30 years of fogging, there hasn't been a documented case of the spray harming anyone.
"It's not known for knocking out anything bigger than a housefly," he said. "We know more about these products going out than we do of what's sold over the counter as herbal remedies."
Parman acknowledged that "for folks concerned, that probably doesn't help."
Schmid and others believe that known and unknown adverse effects of pesticides such as the pyrethroid outweigh what they call a rare and usually not-so-severe human West Nile infection. Just over 4,000 cases have been documented in humans statewide since the disease appeared in 2003, with 145 fatalities.
Nineteen of those cases were from Santa Clara County, with two last year, although none of those people died. In the Bay Area, Contra Costa County historically has seen the most, with 47 diagnosed cases and two fatalities, both in 2006. Nine human cases have been reported statewide this year, three in both Stanislaus and Tulare counties and one each in Fresno, Solano and Contra Costa counties. People older than 50 have a higher chance of getting sick and are more likely to develop serious symptoms.
But Deborah Bass of Contra Costa County Mosquito and Vector Control said, "West Nile virus is grossly underreported." She cited a Centers for Disease Control study that showed for every person diagnosed with a severe case, 70 more may have thought they'd just had a nasty bout with the flu.
"We estimate, based on the CDC data, that as many as 350 people had West Nile virus last year in Contra Costa County," Bass said. "They just didn't know it or it wasn't tested for or reported."
Vector control officials say the virus isn't something to sneeze at.
"Even its mild form averages 16 days off work," Parman said. "It's not the common cold. And for a small percentage it gets neuroinvasive -- we're talking encephalitis. It's a very significant disease."
Fogging opponents cite studies that show pesticide exposure can lead to respiratory and neurological disorders, including a recent UC Davis study that linked use of pyrethroids in agricultural fields with increased incidence of autism in children whose mothers were exposed while pregnant.
"We don't know what effect West Nile virus has during pregnancy," said Alycia Halladay, senior director of environmental and clinical sciences with Autism Speaks.
"On the other hand, you want to avoid pesticides because there's a small increased risk of having a child with autism after exposure. It's damned if you do, damned if you don't."
More information and statistics on West Nile virus are available at:
Residents can avoid the risk of West Nile virus exposure by minimizing contact with mosquitoes. Vector control officials advise: