SONOMA COUNTY, Calif. (KTVU) - West Nile virus, already surging in California, has shown up in Sonoma County, twice in three days.
Friday, two traps in Cloverdale contained mosquitos that tested positive. Wednesday, two traps in Petaluma were also found with infected mosquitos.
They are the first in Sonoma County this year, and officials fear, a bellweather of what's to come as the summer season, and the drought, create prime conditions.
"We have traps set, associated with each one of these wetlands," said Erik Hawk of the Marin/Sonoma Mosquito Vector Control District, looking out over the marshes of the Ellis Creek Wastewater treatment facility, near the Petaluma River.
The area is lined with hiking paths, and popular with bird-watchers and dog-walkers.
Warning signs are posted, alerting them to the discovery of infected mosquitos.
"Dry ice at the top of the trap creates carbon dioxide, which attracts the mosquito, because they think it's a person breathing," explained Hawk, as he demonstrated a trap dangling from a tree.
"There's a light and then a fan on this trap," he continued, "and they get close enough the fan sucks them down into a collection net."
West Nile virus is evident in 30 California counties, a third more than this time last year.
"These drought conditions make it different," elaborated Hawk, "These species that tested positive for the virus, we found them in higher abundance and earlier than normal."
The drought means there is less water, warmer water, and stagnant water.
Birds and mosquitos are sharing it, and they spread the virus between them.
Then, when a mosquito feeds on a person, instead of a bird, humans become infected.
"Some people had to be hospitalized and there were a number of deaths," Phil Smith of the Mosquito Vector Control District told KTVU, at the lab in Cotati.
Smith was describing 2014, when 31 people died of the virus in California.
About 800 human cases were confirmed, double the number of the year before.
"Approximately four out of five people infected with the West Nile will have no symptoms at all," explained Smith, "but when people do get the virus it can be quite serious and the cases of severe disease are increasing over the last few years."
Field testing throughout the North Bay takes on new urgency now, and so do the advisories for the public: dump standing water, wear long sleeves and long pants, or wear repellent where mosquitos are active and especially at dusk and dawn when they are looking for a blood meal.
That can mean an itchy bite, or at worst, a flu-like virus.
"We know it's around," declared Linda Wittcop, walking her dog Sophie, around the wetlands, "I live in the country, I've seen dead birds over the years, so absolutely, I'm concerned."