This undated file electronmicrograph from the official U.S. Department of Defense anthrax information Web Site shows Bacillus anthracis vegetative cells in a monkey spleen. Anthrax is an infectious disease caused by the spore-forming bacteria Bacillus anthracis. The Centers for Disease Control and Prevention said Thursday, June 19, 2014, that some of its staff in Atlanta may have been accidentally exposed to dangerous anthrax bacteria because of a safety problem at some of its labs. (AP Photo/Anthrax Vaccine Immunization Program, File)