Jan. 15 -- Usually associated with the massive waves of "black death" that swept across Europe during the Middle Ages, the plague still occurs occasionally in the United States, though it is treatable with modern antibiotics.
The disease, caused by a bacterium called Yersinia pestis, most often is transmitted to humans through rodent flea bites or by handling infected animals.
Weaponizing the Plague
Experts are skeptical that the plague would make a good bioterror agent.
"It is possible, but difficult, to effectively weaponize Y. pestis," said John D. Clements, professor and chair of the program in molecular pathogenesis and immunology at the Tulane University School of Medicine in New Orleans.
"The only effective way would be to aerosolize the organisms and this would be much more difficult than for anthrax," he added. "This is mostly due to the fact that, unlike Bacillus anthracis, Yersinia do not make spores. Keeping the organism suspended at a high enough concentration, at the right particle size and viable is problematic."
However, a fact sheet on the U.S. Centers for Disease Control and Prevention's Web site notes that if someone with "advanced knowledge and technology" were somehow able to aerosolize the bacterium, it could cause damage.
"Yersinia pestis used in an aerosol attack could cause cases of the pneumonic form of plague," the CDC says. "One to six days after becoming infected with the bacteria, people would develop pneumonic plague. Once people have the disease, the bacteria can spread to others who have close contact with them. Because of the delay between being exposed to the bacteria and becoming sick, people could travel over a large area before becoming contagious and possibly infecting others. Controlling the disease would then be more difficult."
Pneumonic plague differs from bubonic plague in its symptoms and the fact that it can be spread through the air rather than just by contact.
Unlike bubonic plague, pneumonic plague can be spread from person to person. According to the CDC, "Pneumonic plague affects the lungs and is transmitted when a person breathes in Y. pestis particles in the air."