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Biological Agents as Weapons


James M. Madsen

, MD, MPH, U.S. Army Medical Research Institute of Chemical Defense (USAMRICD)

Last full review/revision Feb 2021| Content last modified Feb 2021
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Biological warfare (BW) 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 (including development of strains resistant to multiple drugs). The area of most concern is the use of BW agents by terrorist groups. Biological-warfare agents are thought by some to be an ideal weapon for terrorists. These agents may be delivered clandestinely, and they have delayed effects, allowing the user to remain undetected.



It can be difficult to distinguish use of a biological-warfare (BW) agent from a natural outbreak of disease. Clues to the deliberate rather than a natural origin of a disease outbreak include the following:

  • Cases of diseases not usually seen in the geographic area

  • Unusual distribution of cases among segments of the population

  • Significantly different attack rates between those inside and those outside buildings

  • Separate outbreaks in geographically noncontiguous areas

  • Multiple simultaneous or serial outbreaks of different diseases in the same population

  • Unusual routes of exposure (eg, inhalation)

  • Zoonotic disease occurring in humans rather than in animals

  • Zoonotic disease occurring first in humans and then in its typical vector

  • Zoonotic disease arising in an area with a low prevalence of the typical vector for the disease

  • Unusual severity of disease

  • Unusual strains of infectious agents

  • Failure to respond to standard therapy

Epidemiologic investigation of cases and cooperation with law-enforcement resources are crucial, as is risk communication to the general public.

The clinical presentation, diagnosis, and treatment of patients with disease caused by high-risk BW agents are discussed elsewhere in The Manual: anthrax Anthrax Anthrax is caused by the gram-positive Bacillus anthracis, which are toxin-producing, encapsulated, facultative anaerobic organisms. Anthrax, an often fatal disease of animals, is transmitted... read more Anthrax , plague Plague and Other Yersinia Infections Plague is caused by the gram-negative bacterium Yersinia pestis. Symptoms are either severe pneumonia or massive lymphadenopathy with high fever, often progressing to septicemia. Diagnosis is... read more Plague and Other <i>Yersinia</i> Infections , smallpox Smallpox Smallpox is a highly contagious disease caused by the smallpox virus, an orthopoxvirus. It causes death in up to 30%. Natural infection has been eradicated. The main concern for outbreaks is... read more Smallpox , tularemia Tularemia Tularemia is a febrile disease caused by the gram-negative bacterium Francisella tularensis; it may resemble typhoid fever. Symptoms are a primary local ulcerative lesion, regional lymphadenopathy... read more Tularemia , and viral hemorrhagic fevers Hemorrhagic fevers Categorizing viral infections by the organ system most commonly affected (eg, lungs, gastrointestinal tract, skin, liver, central nervous system, mucous membranes) can be clinically useful,... read more . Management of outbreaks due to biological warfare does not differ from that of natural outbreaks except that clinicians must be alert for unusual antibiotic resistance patterns.

Isolation (of patients) and quarantine (of contacts) may be necessary. The most communicable deliberately disseminated diseases are smallpox (for which airborne precautions are necessary) and pneumonic plague (necessitating droplet precautions).


Because of the relatively long incubation periods of diseases caused by BW agents, most lives will be saved or lost in a hospital setting. Adequate supplies of vaccines, antibiotics, and antivirals for hospitalized patients and for contacts are needed, and systems for distributing such medical countermeasures to members of the general public at high risk of exposure are crucial.

The views expressed in this article are those of the author and do not reflect the official policy of the Department of Army, Department of Defense, or the US Government.

More Information

The following English-language resource may be useful. Please note that The Manual is not responsible for the content of this resource.

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