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Biological weapons have been used since antiquity, with documented cases dating back to the 6th century BC, when the Assyrians poisoned wells with ergots. In the late 1930s and early 1940s, the Japanese Army (Unit 731) experimented on prisoners of war in Manchuria with biological agents that are thought to have resulted in at least 10,000 deaths. Although in 1972 over 100 nations signed the Biological Weapons Convention, both the former Soviet Union and Iraq have admitted to the production of biological weapons, and many other countries are suspected of continuing their programs. Today, bioweapons are considered the cheapest and easiest weapons of mass destruction to produce.

The US government groups bioterrorism agents into three categories: A, B and C. Category A includes organisms or toxins that pose the highest risk to the public and national security because they can be easily spread or transmitted from person to person; result in high death rates and have the potential for major public health impact; might cause public panic and social disruption; and require special action for public health preparedness. Category B agents are the second highest priority: they are moderately easy to spread; result in moderate illness rates and low death rates; and require specific enhancements of CDC's laboratory capacity and enhanced disease monitoring. Category C agents are the third highest priority and include emerging pathogens that could be engineered for mass spread in the future because they are easily available; easily produced and spread; and have potential for high morbidity and mortality rates and major health impact. See

Category A agents (see the following text and Table II–63) include Bacillus anthracis (anthrax), Yersinia pestis (plague), Clostridium botulinum toxin (botulism), Variola major (smallpox), and Francisella tularensis (tularemia), and viral hemorrhagic fevers. All these agents can be weaponized easily for aerial dispersion.


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