Sacramento County officials on Friday dramatically escalated their planned aerial assault on mosquitoes in the face of an extraordinarily high and rapidly rising population carrying the West Nile virus.
Two planes will blanket northern Sacramento County with a pesticides three nights in a row beginning Monday and, as soon as Thursday, will cross the American River to repeat the application across the most populated areas of the southern county, mosquito control officials said.
They said the aerial spraying, originally to be confined to the northern county, was expanded because their surveillance on the numbers of mosquitoes and people infected has been rising daily.
As of Friday, the toll of infected county residents rose to 22, the highest in California.
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Seven of the victims are critically ill, said Dr. Glennah Trochet, county public health officer. Their ages range from 49 to 86. Five others show symptoms of the virus but are not critically ill, she said.
The virus was detected through blood-donor screening in 10 other individuals, who were not aware they had it.
"If we continue at this rate, we absolutely will see a doubling (of cases)," Trochet told The Bee in an interview Friday.
The rate of human infection is driven by the proportion of mosquitoes carrying the West Nile virus, determined by bug traps. That estimated percentage now is four times higher than what state risk-assessment experts consider to be a "high" infection rate, according to David Brown, general manager of the Sacramento-Yolo Mosquito and Vector Control District.
"We are currently finding a very high infection rate - 20 out of 1,000" on average, Brown said Friday at the first public meeting on the aerial spraying plan.
While most of the infected bug population is in the northern county communities, Brown said, "We are starting to see some south of the American River."
To stem the spread of the disease south, vector control officials decided to extend the aerial spraying across the river, perhaps as early as Thursday, Brown said.
The southern spray zone includes all urban areas except Galt, according to Dave Tamayo, a member of the mosquito control board.
Friday's public meeting on the spray plan drew about 50 residents, including some highly vocal critics who persistently interrupted Brown, Trochet and other county officials.
"You're going to kill my bees!" Pat Wade, a north county resident, shouted from the audience in the county supervisors' meeting chambers.
"It's going to kill the spiders!" added Samantha McCarthy of Davis.
"Are you prepared for lawsuits for paint damage?" asked another resident, recalling the fallout from the 1990 helicopter spraying of malathion in Southern California to combat the Mediterranean fruit fly, an agricultural pest.
The officials told critics the decision to go aerial was not easy.
"It's not a knee-jerk reaction," Brown said. "This is a stepped up approach we are using to try to address a public health emergency," he said.
Trochet said the public health benefits of spraying clearly outweigh the risks.
"I cannot look at the citizens of this county and tell them that their lives are going to be put at risk" by exposure to West Nile virus just to avoid "the minimal risk of this amount of (insecticide)," Trochet said.
County officials said the pesticide's active ingredients, pyrethrins, a natural toxin from chrysanthemum flowers, is considered one of the safest insecticides on the market.
The insecticide, which goes by the brand Evergreen EC 60-6, will be heavily diluted from concentrations applied on farms and will be sprayed in droplets smaller than a grain of pollen.
That's large enough to kill mosquitoes and other airborne insects but too small to affect mammals and people, said Dan Markowski, one of a team of specialists with Vector Disease Control Inc., which the county hired to conduct the aerial spraying.
The spray will not kill all the mosquitoes and will not end the virus threat, officials said.
The spray is designed to kill adult mosquitoes that are airborne but not insect larvae on the ground, official said.
Markowski said the planes will dispense two-thirds of an ounce of pyrethrins for every acre sprayed, an "ultra-low" concentration, and that the aerosol will be virtually unnoticeable.
"If you were standing on the ground, and the airplane was flying right over, you might see a very fine mist coming out, but I'd doubt you will feel it," Markowski told The Bee.
A pair of Piper Aztec twin engine planes will release the aerosol from about 300 feet above ground, covering the same 71,000 acres in the north county on each of the three nights. The spraying will last about four hours, between 8:45 p.m. and 12:30 a.m., Markowski said.
He said the pyrethrins formulation is considerably less toxic than the insecticide the company has used in aerial sprays of residential areas to combat the West Nile virus in Houston and mosquito-borne diseases in Miami.
"Last week we treated 189,000 acres in Houston with Dibrom and had no reports of problems," Markowski said.
Facts about the spraying
Q: Who authorized the spraying, and why?
A: Sacramento Yolo Mosquito and Vector Control District General Manager David Brown said he is calling for aerial spraying because the infection rate of mosquitoes is very high in certain areas - as many as one in 10 mosquitoes are carrying the virus - and he wants to prevent an epidemic.
Q: How will I know when my neighborhood is being sprayed?
A: The district is scheduled to begin spraying Monday night, weather permitting. It hopes to cover all 71,000 acres of the target area with two aircraft working from about 8:30 p.m. to 11 p.m. If conditions are right, the district will repeat the spraying over the target area on Tuesday and Wednesday during the same hours.
Q: Why are they repeating the treatments?
A: District spokeswoman Jennifer Benito said the first treatment is expected to kill only 35 percent of the mosquito population. District officials want a higher "kill rate."
Q: What kind of weather do they need to spray?
A: Light winds of less than 8 mph.
Q: Who is doing the spraying?
A: The district is contracting with Vector Disease Control Inc., a company with offices in Arkansas, Missouri and Florida. VDCI will use Piper Aztecs, twin-engine fixed-wing craft, to spray small droplets of pesticide from heights of 150 to 500 feet.
Q: How much does the treatment cost?
A: $1 million, paid by the vector-control district.
Q: Will other parts of the county be sprayed?
A: The district plans to begin aerial spraying in the southern half of the county as early as Thursday.
Q: What pesticide is being used?
A: Its commercial name is Evergreen 60-6. The active ingredients are pyrethrins, an extract of chrysanthemums. Exposure to pyrethrins is considered relatively safe for mammals. At the concentrations being used - 0.66 ounces per acre - it poses no risk to people or most pets, Brown said.
Q: Will it harm the paint on cars or fabrics in outdoor furniture?
A: Brown says it won't.
Q: Is it safe to be outside during spraying, then?
A: Brown said it is always prudent to stay inside when pesticides are being applied. However, he said that no other precautions, such as turning off air conditioners, are necessary.
Q: I signed up with the district not to be sprayed. How will they avoid my house?
A: Brown said the district probably will not be able to honor those requests.
Q: How dangerous is West Nile virus?
A: The virus has a broad range of possible effects. Most people who are infected won't even know it. About one in five will develop symptoms similar to the flu - fever, aches and fatigue. One in 150 develop potentially fatal neurological problems, such as encephalitis and meningitis.
Q: How many people have come down with West Nile virus this year?
A: At last count, 102 throughout California. Sacramento County has the single greatest number of cases, at 22.
Q: How do I get more information?
A: Go to www.sacbee.com/links
- Bee staff writers Chris Bowman and Edie Lau
About the writer:
- The Bee's Chris Bowman can be reached at (916) 321-1069 or firstname.lastname@example.org.