Experts from the U.S. Centers for Disease Control and Prevention are helping Dallas County review the effectiveness of ground and aerial mosquito spraying to combat West Nile virus.
CDC spokesman David Daigle said the federal agency is working with city, county and state health officials to evaluate samples from mosquito traps posted around Dallas County.
"We have baseline data -- what was in the traps before the spraying," he said. "Now we can see what's in the traps after the spraying."
A more detailed CDC report due later this week will provide a more accurate picture to evaluate whether more aerial spraying is justified after the first round was completed in Dallas County last week.
Early samples indicate that ground and aerial spraying efforts have been successful.
"That is great news, but we need to wait for the CDC preliminary numbers that are scientifically significant," Dallas County Judge Clay Jenkins said.
Jenkins said more than 1 million acres in Dallas County have been covered either by planes or trucks and that the county has received no reports of human illness as a result of the spraying.
"All of the science indicates this was safe," Jenkins said. "Now we're going to look to see just how effective it was."
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The ultimate goal is to reduce the number of human West Nile virus cases. Dallas County reports 300 human cases and 12 deaths.
"There will need to be a complete analysis, one that wraps in the human cases, because that's a big part of this, but that would probably take a couple months," Daigle said.
The long-term CDC study will also ask why North Texas has the nation's worst West Nile virus outbreak.
"It just could be a perfect storm situation where you didn't have a hard freeze, the water conditions were just right, it favored the birds or mosquitoes," Daigle said. "When those two work together, unfortunately, it can make a perfect storm and, we really did have kind of a perfect storm in Dallas."
In the short term, positive samples of disease carrying mosquitoes continue to bring ground spraying in Dallas County.
Portions of Lancaster and Irving are scheduled for ground spraying Tuesday and Wednesday.
Officials urge North Texas residents to continue taking precautions to avoid mosquito bites, including long sleeves and pants, insect repellent and removing standing water where mosquitoes breed.
"The season's going to continue for awhile, and whether we knock down some of the mosquitoes, they're still out there," Daigle said.
