United States Department of Homeland Security

“ Natural Outbreaks of Disease Naturally occurring outbreaks of category A agents have become rare because of improved living standards, hygiene, and health services in developed nations. For example, human bubonic plague,which was transmitted by rats and fleas to humans in past centuries resulting in large losses of life, has virtually been wiped out. However, agents used in an aerosol attack may act differently than naturally occurring outbreaks and could produce a form of the disease with a shorter time of onset of illness, making timely diagnosis, treatment, and containment more difficult. ”

“ Historical Perspective on Biological Attack In 2001, anthrax attacks through the U.S. mail infected 11 people with inhalational anthrax, of which five died. An additional 11 people were infected with cutaneous (skin) anthrax, of which there were no fatalities. In the 1990s, the cult Aum Shinrikyo failed in its attempts to release anthrax and botulinum toxin in Tokyo but did succeed in a chemical attack with Sarin nerve agent. ”