The planes will spray a triangular area bound by the Dallas North Tollway, the George Bush Turnpike and Interstate 30. The area includes Richardson, Garland and parts of Dallas and Mesquite. This priority area was established based on disease prevalence and city input and will follow a defined grid pattern for flight efficiency. Five planes are scheduled to fly Friday night and possibly over the weekend to cover the remaining requested areas. A second round of spraying may occur early next week depending on post-spray mosquito counts. “Aerial spraying is a safe and very effective tool, but it doesn’t take the place of the basic precautions," said Dr. David Lakey, DSHS commissioner. “We are urging people to continue using insect repellent every time they go outside.” Texas has more than 400 state-confirmed cases of West Nile illness for 2012, including 17 related deaths. Texas is on track to have the most cases of West Nile illness since the disease first emerged in the state in 2002. Humans can contract West Nile virus from a mosquito bite. The virus can cause serious illness or death. For people concerned about exposure during aerial spraying, health officials suggest the following precautions: • Minimize exposure. Avoid being outside, close windows and consider keeping pets inside while spraying occurs. • If skin or clothes are exposed, wash them with soap and water. • Rinse homegrown fruits and vegetables with water as a general precautionary measure. • Cover small ornamental fish ponds. • Because the chemical breaks down quickly in sunlight and water, no special precautions are suggested for outdoor swimming areas.