If human cases of plague do turn up -- as they sometimes do naturally in the wild -- countermeasures will be taken, Roebuck added. If diagnosed early, for instance, bubonic plague can be treated with antibiotics.
But regardless of the health threat in this case, Stephen Albert Johnson, director for the Center for Innovations in Medicine at Arizona State University's Biodesign Institute, said the missing mice incident raises questions about increased federal bioterror prevention research.
"Risk [from the missing mice] is low, but this is a very bad incident in regard of control," Johnson said. "One of the implications of our bringing a lot more people and money in to work on threat agents is that more of these types of incidents are likely to happen."
Researchers in federal bioterror facilities already are given background checks and have to go through an approval process for safety and security protocols, Roebuck said. In addition, the CDC conducts site visits to ensure labs are secure and following protocol.
In addition, Roebuck added, the CDC continues to investigate the missing mice to determine what, if anything, can be done to avoid a repeat of the incident.
ABC News' Pierre Thomas, Richard Esposito, Roger Sergel and Michael S. James contributed to this report.