"There is no indication that this is a public health threat," said Jennifer Morcone, a CDC spokeswoman.
According to the CDC and other federal agencies, plague - including the bubonic, septicemic and pneumonic forms - is contracted by 10 to 20 people in the U.S. each year. Most become infected after being bitten by fleas or rodents in the southwestern U.S., where bubonic plague frequently infects prairie dogs.
Bubonic plague rarely spreads from human to human. But when it enters the lungs and becomes the pneumonic form, it can be spread to others when the infected person sneezes or coughs.
Because of fears that terrorists could use plague as a bioweapon, the federal National Institutes of Health - which paid for the testing involving these mice - has increased funding substantially for research into plague and vaccines for treating it.
But as yet, said Garrett, no one appears to have found a way to make a deadly plague aerosol spray that could be used in terrorist attacks.
The potential vaccine was a failure, Perlin added.