On Oct. 17, Brenda Brantley, an employee at Texas' Health and Human Services Commission, was in her second-floor office at the agency’s Austin headquarters when she received an unexpected visitor.

The beady-eyed infiltrator — a brown rat of the species Rattus norvegicus — scurried down the carpeted hallway before ducking behind a filing cabinet, employee correspondence shows.

The sight was sufficiently disturbing to health commission workers that Hugh Addington, the agency's director of cross-division coordination, fired off a note to executive leadership, detailing the intruder’s exact movements before it disappeared.

“It could not be located,” Addington lamented in an email obtained by The Texas Tribune under public records law. But the rodent left a clue as to its whereabouts. “There are also droppings nearby in cube 2123,” Addington wrote.

In subsequent weeks, the Norwegian rat — also known as a street rat or sewer rat — seems to have invited its friends and family over, too. A health commission spokeswoman estimated there are now “several hundred in the building.”

The agency is facing a $60,000 bill to pay private exterminators from Orkin for the quixotic task of trapping and killing the remaining rodents in the building. That's in addition to pest control work already undertaken by the Texas Facilities Commission.

Employees described to the Tribune seeing trapped rat corpses in office hallways. Some shared harrowing cellphone photos of the furry creatures’ mangled bodies. But perhaps most disturbing, employees said, are the myriad live rat sightings.

“This is really unsettling the staff...” Lesley French, an associate commissioner at the agency, wrote in an email on Oct. 20, in which she forwarded Addington’s note to Enrique Marquez and Kelly Garcia, two other high-ranking employees. (Marquez was later spotted in an Orkin Man costume at the agency’s Halloween celebration.)

Garcia then passed along the email to Hailey Kemp, the agency’s deputy chief of staff, as they planned a meeting on how to deal with the four-legged invaders. “Rats on [floor] 2 are a continued problem,” Garcia wrote, appending a sad-faced emoticon.

Just how serious are the agency’s problems? Orkin exterminators take a bleak view. “Rats prefer to hide, given enough space, so if rats are observed in plain sight, it is likely that a full-blown infestation already exists,” reads a post on the company’s website.

To get rid of them, the agency has taken the unusual step of paying out of its own budget for emergency extermination.

“While we have been trapping and working with [the Texas Facilities Commission], we wanted to take the extra step and hire a contractor to address the situation before winter,” said Christine Mann, a health agency spokeswoman.

Normally, the facilities commission would handle these sorts of issues for its sister state agencies. The facilities commission has a full-time employee licensed in pest management and, as a backup, a list of private contractors it can call for help. The health commission’s decision to hire its own contractor left the facilities commission nonplussed, emails show.

“We understand that HHSC has a bid of @ $60K for Orkin to do something, but not exactly clear what,” wrote Peter Maass, the Texas Facilities Commission’s deputy executive director of planning and real estate management.

“Also, do not understand why a pest control contractor is being hired directly by HHSC and not routing through TFC,” he wrote.

Then there is the question of where the pests came from. The facilities commission believes the rats “may be largely associated with ongoing renovation/minor construction activities,” Shyra Darr, that agency’s director of strategic planning and policy, wrote in an email. “In general, minor construction and deferred maintenance activities often disrupt and reveal rodent issues in any building.”

Internally, health agency officials have told employees to clean up their desks, especially of food waste. An all-staff email sent on Oct. 23 to Department of State Health Services employees, who face pest control problems of their own, encouraged employees to rat out their colleagues via an anonymous tip line.

“Your call will be kept confidential,” the email stressed.

The Health and Human Services Commission is a massive operation, spanning roughly 60,000 employees and an $80 billion two-year budget. Its duties include administering Medicaid, the public health insurance program that serves roughly 4 million Texans at any given time, and regulating certain health care providers. On the latter point, the agency also inspects various health care facilities to ensure they're clean enough to protect the sick and elderly patients they serve.

The irony of health care regulators being overrun by rats is not lost on state employees. Mann, the agency spokeswoman, conceded that if a rat infestation were discovered at one of the buildings regulated by the state, such as a nursing home or mental hospital, it “could be cited for unsanitary conditions.”

Pests are nothing new in state government buildings. In 2014, at the Texas School for the Deaf, regulators found living and dead rodents strewn about the building. There were raccoon, squirrel and possum carcasses in crawlspaces, along with rats and rat feces. In that case, the state spent $18,000 on extermination.

But the health commission infestation appears to be in a league of its own. Darr, of the facilities commission, said she was not aware of another state building that had a rat problem as extensive as Brown-Heatly's.

Seth Hutchinson, organizing coordinator for the Texas State Employees Union, said the structural and pest control problems at state government buildings were the result of decades of under-investment.

"It’s not just HHSC," he said. "The general state of repair of state buildings is pretty poor."

State agencies can ask lawmakers for emergency funds from the budget to handle “deferred maintenance” costs. But Mann said the health commission had no plans to ask for pest control funds in the agency’s next legislative appropriations request, expressing confidence that the rat problem would be taken care of by winter’s end.