The Knox County Health Department has added the Rocky Hill area of west Knoxville to its mosquito spray zone this week after mosquitoes in that area tested positive for West Nile Virus.

The health department will spray for mosquitoes in the area on Thursday, Oct. 13 between 9 p.m. and midnight, weather permitting.

Signs will be posted in the affected neighborhood, and residents are asked to stay, and keep pets inside or in the backyard, inside during the spraying.

Cooler temperatures are keeping some mosquitoes at bay, but mosquitoes will still be in the area until the first hard frost, said KCHD Vector Control Supervisor Andrea Woodard.

"So mosquitoes really depend on the weather," Woodard said. "They are going to stick around until we have a really hard frost. They aren't as active if the temperature drops below 55 degrees, but until we get a really good frost, we are still going to have mosquitoes flying around."

The average first frost in Knoxville is Oct. 17, according to the National Weather Service.

KCHD crews will also spray the Fairmont Boulevard and Fourth Avenue areas Thursday night.

More information about mosquito spraying and West Nile Virus can be found on the KCHD website.