After three evenings of spraying pesticide over the skies of south Sacramento and Elk Grove, West Nile warriors will have to wait until next week to learn if the treatment cut down on infected mosquitoes.
It will take that long to finish a series of before-and-after mosquito trapping and testing in the sprayed areas, said Gary Goodman, assistant manager of the Sacramento-Yolo Mosquito and Vector Control District.
The district hopes it won't need to do more aerial spraying over urban areas this season, but it cannot be certain, Goodman said.
"Unfortunately, my answer is going to change every single day," he said, as new data comes in from dead bird testing, mosquito trap analyses and health departments that track human cases.
People are likely to get at least one day's warning before any additional spraying, though, because it would take a day for the planes to arrive here from other areas.
While the mosquito district has long sprayed pesticide from planes over agricultural fields and from the ground using trucks or hand crews, it only began dousing urban areas with mosquito killing chemicals by air in 2005.
That was the year that West Nile virus began spreading broadly in Northern California, and Sacramento was especially hard hit. The disease most commonly passes with no symptoms, but it can be deadly or permanently disabling.
Reported human cases, which usually involve either more severe symptoms or detection during routine blood donation, peaked at 880 in California in 2005. Nineteen people statewide died of West Nile that year.
Last year there were 380 reported human cases and 21 deaths, and so far this year there have been six reported cases and no deaths, according to the state Department of Public Health.
To combat the disease, the Sacramento-Yolo district has sprayed the same pesticide, Evergreen Crop Protection EC 60-6, over selected urban areas for the last four summers. After a delay to let smoke from wildfires dissipate, this year's aerial spraying began last Wednesday and continued through Friday.
West Nile virus often accelerates in late July, and the Placer Mosquito and Vector Control District said Monday it has confirmed its first signs of infection – a dead bird in Roseville and infected mosquitoes in Lincoln.
In the Sacramento-Yolo area, signs of the disease came earlier than usual.
The first dead bird that tested positive for West Nile was found in Wilton in March, while typically the first one hasn't been spotted until June, said district spokeswoman Luz Maria Rodriguez.
Those early signs make it especially important for people to take precautions, she said.
"We're relying on the public to let us know of any mosquito breeding sources - … abandoned homes that might have pools, spas, things of that nature," she said. "And we're hoping people take good care of their own homes."
Along with eliminating sources of standing water where mosquitoes breed, the district is encouraging people to wear long sleeves, long pants and mosquito repellant if they venture out at dawn or dusk, when mosquito activity is at its peak.
Call The Bee's Carrie Peyton Dahlberg, (916) 321-1086.
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