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 medications). 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 U.S. Centers for Disease Control and Prevention (CDC) has prioritized biological agents and toxins into 3 groups: A (highest priority), B, and C (see table ) (1).
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 and pneumonic plague are the 2 diseases most likely to occur under these circumstances.
CDC High-Priority Biological Agents and Toxins*
Category | Agent |
|---|---|
A: Highest priority | Bacillus anthracis, causing anthrax Botulinum toxin from Clostridium botulinum, causing botulism Yersinia pestis, causing plague Francisella tularensis, causing tularemia Variola virus, causing variola major (classic smallpox) Viral hemorrhagic fever (VHF) viruses:
|
B: Second highest priority | Brucella species, causing brucellosis Epsilon toxin of Clostridium perfringens causing food poisoning Salmonella causing food poisoning; Escherichia coli O157:H7; and Shigella, causing shigellosis Burkholderia mallei, causing glanders Burkholderia pseudomallei, causing melioidosis Chlamydia psittaci, causing psittacosis Coxiella burnetii, causing Q fever Ricin toxin from Ricinus communis Staphylococcal enterotoxin B causing staphylococcal food poisoning Rickettsia prowazekii, causing typhus fever Alphaviruses causing viral encephalitides (eg, Venezuelan, eastern, and western equine encephalitides) Vibrio cholerae, Cryptosporidium parvum, and other agents, causing waterborne diseases (eg, cholera, cryptosporidiosis) |
C: Third highest priority | Nipah virus, hantavirus, coronaviruses, and influenza viruses capable of causing pandemic influenza Other agents associated with emerging infectious diseases |
* An alphabetical listing of bioterrorism agents and diseases can be found at Centers for Disease Control and Prevention: Biological and chemical terrorism: strategic plan for preparedness and response. Recommendations of the CDC Strategic Planning Workgroup. MMWR Recomm Rep. 2000;49(RR-4):1-14. | |
(See also Overview of Incidents Involving Mass-Casualty Weapons.)
General reference
1. Centers for Disease Control and Prevention: Biological and chemical terrorism: strategic plan for preparedness and response. Recommendations of the CDC Strategic Planning Workgroup. MMWR Recomm Rep. 2000;49(RR-4):1-14.
Recognition of Biological Weapon Injuries
It can be difficult to distinguish use of a BW agent from a natural outbreak of disease. Clues to a deliberate rather than a natural origin of a disease outbreak include the following (1):
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, plague, smallpox, tularemia, and viral hemorrhagic fevers. 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 diseases that may be deliberately disseminated are smallpox (for which airborne precautions are necessary) and pneumonic plague (necessitating droplet precautions). The practical differences between airborne and droplet precautions primarily relate to room ventilation and levels of respiratory protection. Details of contact, airborne, and droplet precautions are available from the CDC (2).
Recognition references
1. Karwa M, Currie B, Kvetan V. Bioterrorism: Preparing for the impossible or the improbable. Crit Care Med. 2005;33(1 Suppl):S75-S95. doi:10.1097/01.ccm.0000151070.56915.22
2. Siegel JD, Rhinehart E, Jackson M, et al; Health Care Infection Control Practices Advisory Committee. 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Health Care Settings. Am J Infect Control. 2007;35(10 Suppl 2):S65-S164. doi:10.1016/j.ajic.2007.10.007
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 (which can be effective during the incubation period for several agents) (1), 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 (2).
Response references
1. Gallagher T, Lipsitch M. Postexposure Effects of Vaccines on Infectious Diseases. Epidemiol Rev. 2019;41(1):13-27. doi:10.1093/epirev/mxz014
2. Powers S, Escajeda J, Glauser J. Updates to Disaster Management Strategies for CDC Category A Bioterrorism Agents. Current Emergency and Hospital Medicine Reports. 2024 Apr 22:1-7
