Biological warfare is the use of microbiological agents for hostile purposes. Such use is contrary to international law and has rarely taken place during formal warfare in modern history, despite the extensive preparations and stockpiling of biological agents carried out during the 20th century by most major powers. For a variety of reasons (including uncertain military efficacy and the threat of massive retaliation), experts consider the use of biological agents in formal warfare unlikely. The area of most concern is the use of such agents by terrorist groups. Biological agents are thought by some people to be an ideal weapon for terrorists. These agents may be delivered clandestinely, and they have delayed effects, allowing the user to remain undetected.
Potential biological agents include anthrax, botulinum toxin, brucellosis, viruses, hemorrhagic fever viruses (Ebola and Marburg), plague, tularemia, and smallpox. Each of these agents is potentially fatal and, except for anthrax, botulinum toxin, and tularemia, can be passed from person to person; direct person-to person transmission of brucellosis is extremely rare. Anthrax is of most concern; anthrax spores are relatively easy to prepare and spread through the air, creating the potential for distribution by airplane. Theoretically, 1 kg of anthrax could kill 10,000 people, although technical difficulties with preparing the spores in a sufficiently fine powder would probably limit actual deaths to a fraction of this number. Some other potential agents, including Yersinia pestis, Francisella tularensis, viral hemorrhagic fever viruses, smallpox virus, and botulinum toxin, can potentially be aerosolized as bioweapons.
Despite these theoretical concerns, the only successful terrorist use of anthrax—multiple pieces of contaminated mail delivered to a variety of locations in the US in 2001—resulted in only a handful of deaths and serious infections (total of 22 cases). A larger number of people were contaminated with anthrax spores without developing illness. However, there was extreme public anxiety related to these incidents.
In addition to the actual infections, an even greater number of false threats of anthrax have been reported. In 1999, the FBI received an average of 1 false report/day of alleged anthrax use. False reports, both hoaxes and alarmed citizens misperceiving harmless material for anthrax, increased even more after the 2001 anthrax attack in the US.
The only other successful use of a biological agent by a terror group in the US occurred in 1984. In this event, 751 people were stricken with diarrhea when a salad bar in Oregon was intentionally contaminated with Salmonella. The bacteria were introduced by a religious cult trying to influence the results of a local election. No one died, and the election was not affected.
Defense against bioterrorism involves several factors:
Last full review/revision October 2012 by Allan R. Tunkel, MD, PhD
Content last modified November 2012