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.
The US Centers for Disease Control and Prevention (CDC) has prioritized biological agents and toxins into 3 groups: A (highest priority), B, and C (see table CDC High-Priority Biological Agents and Toxins CDC High-Priority Biological Agents and Toxins* 
).
The deliberate use of BW agents to cause mass casualties would probably entail dissemination of aerosols to create disease via inhalation, and thus inhalational 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 
and pneumonic plague Plague and Other Yersinia Infections Plague is caused by the gram-negative bacterium Yersinia pestis. Symptoms are either severe pneumonia or large, tender lymphadenopathy with high fever, often progressing to septicemia... read more 
are the 2 diseases most likely to occur under these circumstances.
(See also Overview of Incidents Involving Mass-Casualty Weapons Overview of Incidents Involving Mass-Casualty Weapons Mass-casualty incidents (MCIs) are events that generate sufficiently high numbers of casualties to overwhelm available medical resources. They include natural disasters (eg, hurricanes) and... read more .)
Recognition of Biological Weapon Injuries
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 , plague Plague and Other Yersinia Infections Plague is caused by the gram-negative bacterium Yersinia pestis. Symptoms are either severe pneumonia or large, tender lymphadenopathy with high fever, often progressing to septicemia... read more , smallpox Smallpox Smallpox is a highly contagious disease caused by the smallpox virus, an orthopoxvirus. Case fatality rate is about 30%. Natural infection has been eradicated. The main concern for outbreaks... read more 
, 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 
, 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).
Response to Biological Weapon Injuries
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.
Centers for Disease Control and Prevention: Emergency Preparedness and Response: An alphabetical listing of bioterrorism agents and diseases. Accessed January 4, 2023.
