A months-long investigation into a rural California warehouse uncovered an illegal laboratory that was filled with infectious agents, medical waste and hundreds of mice bioengineered “to catch and carry the COVID-19 virus,” according to Fresno County authorities.

Health and licensing said Monday that Prestige Biotech, a Chinese medical company registered in Nevada, was operating the unlicensed facility in Reedley, California — a small city about 24 miles southeast of Fresno. The company, according to Reedley City Manager Nicole Zieba, had a goal of being a diagnostics lab.

“They never had a business license,” Zieba told USA TODAY. “The city was completely unaware that they were in this building, operating under the cover of night.”

The Fresno County Public Health Department launched its investigation into the facility in December 2022 after a code enforcement officer saw a garden hose attached to a building that was presumed to be vacant and had no active business license, Zieba said.

Further inspection in March revealed that the facility housed various chemicals, suspected biological materials, bodily fluids and hundreds of lab mice, among other lab supplies, according to court documents.

County public health officials said they also found medical devices that were believed to have been developed on-site, such as COVID and pregnancy tests.

“Being a small, rural town of 26,000 — walking into what we believed to be a vacant building and finding lab supplies, live white mice… was was fairly shocking,” Zieba said.