Two small twin-engine aircrafts quietly sprayed mosquito-killing chemicals over University Park, Highland Park and several other Dallas communities overnight in an emergency effort to stop the spread of the deadly West Nile virus that has claimed 15 lives in the D-FW area.
Now the question on the minds of many neighborhood residents is this: Did it work? 
“The disease poses an immediate public health threat to Dallas County. We need to use all possible tools, including aerial spraying, to fight this outbreak,” said Dr. David Lakey, DSHS commissioner. “We will support the decisions made by local officials as we work together to confront this situation.”
Public health officials say additional rounds of aerial spraying may be necessary if measurements, such as an increase in West Nile cases, indicate more of the aggressive eradication effort is wise.
Spray droplets must touch the mosquitoes to kill them. Aerial spraying is the most effective means to kill new habitats of mosquitoes that might move into the spray zone from outside, officials say. Such “re-infestations” are common, public health officials say.
In addition to the Park Cities, aircrafts sprayed the Dallas neighborhoods of Preston Hollow, Lakewood and Lake Highlands sections of Dallas. Spraying was scheduled from 10 p.m. to 1 a.m. and was expected to cover the area bounded by Interstate 635 to the north and east, the Dallas North Tollway to the west and Interstate 30 to the south.
Also sprayed overnight were Richardson, Garland and Mesquite north of Interstate 30. Because of rain last night, the cities Richardson, Garland and Mesquite were not sprayed, but will be on Friday, weather permitting.
Aerial spraying is scheduled Friday night in Coppell, weather permitting. Other cities will likely to be added to the list.
Flying 300 feet above the ground at a speed of 170 mph by pilots wearing military spec night vision goggles, the planes spewed a chemical mist called Duet, approved by the U.S. Environmental Protection Agency in 1995 as safe to help control large adult populations of mosquitoes.
Duet poses no harm to humans or pets because the concentrations are just high enough to kill mosquitoes, which are active at night.
Nonetheless, officials had urged residents during the spraying to stay inside, keep pets indoors, use soap and water to wash skin and clothes that might have come in contact with the spray; clean fruits and vegetables that might have been exposed to the spray; and to make sure ornamental fish ponds were covered prior to the spraying.
Nearly half of all West Nile cases in the United States so far this year are in Texas, according to the Centers for Disease Control and Prevention. If the trend continues, 2012 will be the worst West Nile year in state history.
Because of the severity of the outbreak, the Texas Health Department is stepping in to oversee the effort and to pay for it.
"This year is totally different from the experience Texas has had in the past," state Health Commissioner Dr. David Lakey told reporters. "If it's nuisance mosquitoes, we ask the city or county to pay part of that. But in the midst of this disease outbreak, it's easier for us to go ahead and do it.”
Health officials have pointed to what they say have been successful aerial spraying efforts in Sacramento, CA, Louisville, KY and Houston to combat West Nile.
According to media reports, the results were mixed in Sacramento, which endured a 2005 West Nile outbreak. In some sprayed areas, about 90 percent of the mosquito population was wiped out, while in other areas, about 10 percent of the population was killed.
Dallas County health officials are expected to issue a public statement on the results of the overnight spraying.`