NORTH TEXAS (CBSDFW.COM) – While a new virus is still spreading, an old one is coming back.

Mosquito control crews were planning to spray Friday night in two northern areas of Tarrant County as more trapped insects continue to test positive for West Nile virus.

Frisco was also scheduling spraying for Saturday.

Crews sprayed in Arlington earlier in the week, as public health officials said the virus appeared to be poised to make its largest impact since at least 2016.

Since the number of mosquitos testing positive started spiking in June, Tarrant County was reporting 157 positive samples through July 25.

Data from the Texas Department of State Health Services showed Tarrant County had more than twice as many positive results as any other county in the state.

Tarrant County Issues West Nile Virus Public Health Warning: ‘Mosquito Activity At Record High Levels’

“Very unfortunate that we’re starting off the season that way, but it’s a grim reminder we need to be paying attention to everything happening in our community, not just one illness,” said the county’s public health director Vinny Taneja during a presentation to county commissioners Tuesday.

Taneja was referencing the one human case recorded so far, which resulted in a death.

Dr. Joon Lee, with the UNT Health Science Center in Fort Worth, explained it was possible the bird population had turned over, with fewer of them carrying antibodies to the virus.

Mosquitos spread the virus by biting infected birds.

However, everything from temperature, to humidity, to human movement could impact the way the virus spreads.

“So it should be more human cases, we would expect, but just one case,” he said. “But when August comes, we don’t know what’s going to come. We can’t really predict the weather, right?”

Lee said he didn’t want to add more concern for the public, already consumed with COVID-19.

He’s emphasizing preventative measures though, and making recommendations to local governments more actively than he has in the last couple seasons.