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Biological Agents as Weapons

by James Madsen, MD, MPH

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. BW 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 created a priority list of biological agents and toxins (see Table: CDC High-Priority Biological Agents and Toxins). The highest-priority are Category A.

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



A: Highest priority

Bacillus anthracis, causing anthrax

Botulinum toxin from Clostridium botulinum, causing botulism

Yersinia pestis, causing plague

Variola virus, causing variola major (classic smallpox)

Francisella tularensis, causing tularemia

Viral-hemorrhagic-fever (VHF) viruses

  • Arenaviruses, causing Lassa fever and New World VHFs (Machupo, Junin, Guanarito, and Sabia hemorrhagic fevers)

  • Bunyaviridae, causing Crimean Congo hemorrhagic fever and Rift Valley fever

  • Filoviridae, causing Ebola virus disease and Marburg virus disease

  • Flaviviridae, causing yellow fever, Omsk hemorrhagic fever, and Kyasanur Forest disease

B: 2nd highest priority

Brucella species, causing brucellosis

Epsilon toxin of Clostridium perfringens

Salmonella sp, Escherichia coli 0157:H7, and Shigella, causing food poisoning

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

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

C: 3rd highest priority

Nipah virus, hantavirus, SARS coronavirus, and influenza viruses capable of causing pandemic influenza

Other agents associated with emerging infectious diseases

CDC = US Centers for Disease Control and Prevention; SARS = severe acute respiratory syndrome.

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