HOUSTON -

More than 60,000 acres in northwest Harris County were sprayed by air Wednesday to fight West Nile virus.

Officials with the Harris County Public Health and Environmental Services' Mosquito Control division said West Nile virus activity has recently increased. It has been confirmed in more than 300 mosquito samples and nearly 100 dead birds, officials said.

"Harris County is experiencing an increase of West Nile Virus infection in mosquitoes and, most notably, in the dead bird population," Dr. Rudy Bueno said. "This situation has prompted the need to supplement the ongoing countywide ground treatment with aerial treatment in the designated areas to better protect the health of our residents."

Pilot Malcom Williams loaded up his plane Wednesday and flew for more than five and a half hours. He said he will target areas that are tough, if not impossible, to get to by ground.

"We've got approximately 60,000 acres chosen by the Harris County Mosquito control for us to spray tonight to reduce the mosquito count to affect the West Nile Virus factor," said Williams.

"The blocks that we are assigned are put into a GPS system, and it tells the aircraft where to fly," Williams said. "Everything's automatic. Spray comes on, spray goes off, swath line automatically advances. All the pilot has got to do is fly."

He told Local 2, "The ground, if you go down a road, a truck can only spray which ever way the wind is blowing about 300 feet. And when you have mosquitoes over this wide of an area, then it's almost physically impossible to have that many trucks out there spraying to do the job."

The county has reported six human cases of West Nile virus this year. There have been 13 human cases in the city of Houston, and three of those cases were fatal. There have been almost 30 West Nile virus-related deaths in Texas in 2012.

The insecticide that was sprayed is Dibrom, which has been approved by the Environmental Protection Agency. It's considered to be safe for the environment and is routinely used to combat mosquito-borne disease.

Joei Didow is a first-time mom of 10-month-old twins. She said she only uses natural products and she's nervous about the spraying.

"The skin is the largest organ on your body," Didow said. "Anything they touch gets absorbed in the bloodstream. We don't know what the ramifications of the pesticides are."

Health officials said there is no need to worry.

"Because of the very small amount of active ingredient released per acre of ground, the estimates found that for all scenarios considered, exposures were hundreds or even thousands of times below an amount that might pose a health concern," an EPA representative said.

Officials recommended that people stay indoors while their area is being treated, as a precaution.

Authorities also recommend that people take personal measures to avoid being bitten by mosquitoes. It is recommended that people use an insect repellent containing DEET, Picaridin, oil of lemon eucalyptus or IR3535 as an active ingredient. Wearing long-sleeved shirts and long pants at dawn and dusk, when mosquitoes are most active, is encouraged.