In an effort to head off the Valley’s escalating West Nile virus pandemic, Maricopa County has begun spraying adult mosquitoes en masse and may even take the fight to the skies, county officials said.
Maricopa County Supervisor Don Stapley, RDistrict 2 of Mesa, said the county has allocated $1.25 million and has contracted with outside vendors to control mosquitoes in select areas.
"We’re pulling out all the stops," Stapley said. "We’re already out there doing it."
Stapley said the county is seriously considering an aerial assault on mosquitoes to curb the adult population. Colorado, Wyoming and South Dakota used aerial pesticide spraying in 2003 after the virus reached epidemic proportions in those states.
About midway through Arizona’s mosquito season, the number of confirmed human cases of West Nile virus already has risen to 163, with the vast majority of those cases in Maricopa County. Two people have died.
Arizona leads the nation this year by a huge margin in confirmed human West Nile virus infections. Last year’s front-runner Colorado is a distant second with only 30 known cases in 2004 so far.
Last year, the incidence of West Nile virus increased dramatically in September, which Maricopa County vector control supervisor Kirk Dymbrowski said might be because of seasonal bird migrations.
"We haven’t even hit the bad stuff yet," Dymbrowski said of the current season.
In 2003, South Dakota officials sprayed more than a dozen cities from the air with a pesticide called sumithrin, which South Dakota Department of Health officials said was effective in killing 90 percent to 100 percent of the adult mosquito population within an hour of spraying.
Sumithrin, which is approved by the Environmental Protection Agency and is often used for mosquito control, breaks down quickly in the environment, and at the low concentrations used makes the likelihood of any adverse effects very low, according to Iowa State University toxicologists who performed a study on the chemical last year. It is the same active ingredient used in flea and tick collars.
Still, residents with allergies or a low tolerance to pesticides would be advised to stay inside during spraying hours, from dusk to midnight.
Disease control experts disagree on the effectiveness of aerial spraying as a weapon against the West Nile virus. While it does eliminate adult mosquitoes, it does not kill mosquito larvae that will become the next generation of virus carriers, so it is more likely to work in tandem with larvacide use.
Stapley said the Board of Supervisors, which must approve any aerial spraying, would defer to the opinion of local public health experts.
"It really depends on whether it’s deemed to be effective," he said.