Mosquitoes are sorted at the Dallas County mosquito lab in Dallas, Texas on Aug. 16, 2012. Dallas County has seen the highest number of cases of West Nile virus of any county in Texas: 379 this year, as of Oct. 25.
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Technicians with the Contra Costa County Mosquito and Vector Control District spray insecticide in Brentwood, Calif., last month. Workers fogged areas of the county that had an increase in the numbers of mosquitoes carrying the West Nile virus.
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