Bioterrorism is the intentional release or spread of agents of disease.
The agents may be viruses, bacteria, or toxins produced by bacteria.
They may spread through the air, food, or water; or they may come into direct contact with the skin.
Two of the best known bioterrorism incidents in the U.S. occurred early in this century: in 2001, letters containing anthrax spores were mailed to several news offices and two Senate offices.
In 2003, a deadly toxin called ricin was detected in a letter addressed to the White House.
