It could be a week before Dallas County health officials have definite results to judge the effectiveness of aerial mosquito spraying completed this week to combat the nation’s worst West Nile virus outbreak.
Three airplanes took to the skies Thoursday night for the final round of aerial spraying over several muncipalities south of Interstate 30.
Health Director Zach Thompson said early tests indicate ground and aerial spraying conducted so far has been helpful.
"There are small amounts of the mosquitoes carrying the West Nile virus but not at the magnitude we had before, so we think that the aerial spraying and ground spraying has been effective. Now we've got to collect the data," Thompson said.
That data will help determine whether additional aerial spraying would be considered in Dallas County.
The Southern Dallas County city of Lancaster will conduct its first citywide ground spraying for mosquitoes Friday starting at 10 p.m.
Lancaster was not included in aerial spraying and sprayed just one small area of the city adjacent to DeSoto in July.
"The city of Lancaster has not been impacted like other areas north of I-30, so we're only going to do the ground spraying," City Manager Opal Mauldin-Robertson said.
Three confirmed human cases of West Nile virus have been reported in Lancaster. No deaths have been reported.
All of Dallas County has 291 human cases and 11 deaths as of Friday.
Resale shop owner Louise Robertson was back at work on the Lancaster Square Friday after spending a week at home from what she believes was a case of West Nile fever, the less serious form of the virus.
She said she supports ground and aerial spraying.
"I don't see any problem with it," she said. "And they've reassured everybody that it won't hurt animals, it won't hurt bees, and there hasn’t been anything to prove that it has, so I'm for it," she said.
The city manager said other people have mixed feelings.
"We've had people asking, 'Why are you just now spraying?' and I've had people saying, 'Please don't spray," Mauldin-Robertson said.
Lancaster has an additional challenge in fighting mosquitoes that breed in standing water.
Of 300 homes damaged by an April tornado, 28 are still a wreck with no residents to guard against standing water and many places where it can accumulate.
"And so we are looking at inspecting those and, where possible, emptying and draining any standing water, as well as treating any potential standing water hazards," Mauldin-Robertson said.
As the county conducts tests on spraying results, Thompson said residents should not stop taking their own West Nile virus precautions.
"We can't claim victory," he said. We're not out of the woods yet in terms of the mosquitoes."
Precautions include wearing long sleeves and pants and using bug repellant with DEET, especially at dusk and dawn.
NBC 5's Ben Russell contributed to this report.