CLARK — A park in Clark that will host this weeks’s Union County MusicFest, expected to draw tens of thousands of spectators this weekend, has been sprayed for mosquitoes after health officials discovered an insect carrying the West Nile Virus there last week.

A mosquito pool, used by health officials to trap insects for testing, tested positive on Aug. 31, the county said. The pool was located in Oak Ridge Park, the site of the county’s annual free concert festival.

“It is not uncommon to find West Nile Virus in mosquito pools throughout the county, and the state of New Jersey as a whole,” Sebastian D’Elia, a county spokesman, said in an e-mail Thursday afternoon. “When it is found, the site is immediately treated.”

The state Department of Health and Senior Services, as well as local health offices throughout New Jersey, regularly test mosquitoes for the virus. Hundreds of insects regularly test positive, state reports show.

But cases of humans contracting the disease are rare, both the state and county said. In the past several years, there has been only one confirmed human case of the virus in Union County, D’Elia said.

MusicFest started earlier this week but will host its featured acts this weekend. Bands include headliners Train and Spoon, as well as OK GO, Soul Asylum, Suzanne Vega, The Bravery and The Zombies.

D'Elia urged those planning to attend the concerts to take common precautions such as wearing long pants and applying mosquito repellent.