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Johns Hopkins Center for Public Health Preparedness

Biological Weapons

Biological weapons are a subset of a larger class of weapons referred to as weapons of mass destruction (WMD), which also includes chemical, nuclear, and radiological weapons. Biological weapons are unique, in that?a biological weapon attack could potentially result?in an epidemic.

A Different Sort of Response

The response required for bioterrorism is also fundamentally different from that demanded by natural disasters, conventional explosives, chemical terrorism, radiological terrorism (e.g., ?dirty bombs?), or nuclear weapons. Due to the incubation periods of a number of biological agents, the effects of a biological attack may not be noticed for several days after the delivery of the agent against a population?a fact that complicates the public health response to a biological attack compared, for example, to the acutely recognizable results of a chemical attack.

What is a Biological Agent?

Biological weapons have been employed throughout history, with some of the earliest recorded uses dating to the sixth century BCE. [Source:, accessed 4/7/03]. A biological weapon is generally composed of a biological agent or toxin (bacteria, mycoplasma, rickettsiae, viruses, yeasts, fungi), additives to assist with dissemination and stability, and a delivery system. Biological agents can be delivered:

  • as an aerosol
  • by food?or water
  • by a vector
  • by injection

Impact on Health

The health impact of a biological attack depends critically on:

  • type of agent
  • its preparation
  • mode of delivery
  • meteorological conditions (e.g., temperature, wind speed, humidity, sunlight) under which the attack is conducted

Biological weapons can be directed against crops and livestock, in addition to humans.

The Three Categories of Biological Weapons
The CDC separates potential bioterrorism agents that cause infections in humans into three categories, designated as A, B, and C [source:, accessed 4/7/03].

Category A agents carry the highest priority because they:

  • can be easily disseminated or spread person-to-person
  • can be highly lethal
  • have the potential for serious public health impact?
  • can potentially cause public panic and lead to social disruption

Category A agents include the following:

  • anthrax
  • botulism
  • plague
  • tularemia
  • smallpox
  • viral hemorrhagic fevers

Category B agents carry the second-highest priority because they:

  • are moderately easy to disseminate
  • usually result in moderate morbidity
  • are generally less lethal

Examples of category B agents include:

  • brucellosis
  • Q fever
  • ricin toxin
  • cholera

Category C agents carry the third-highest priority. They include emerging pathogens that could potentially be engineered for future mass dissemination.

Examples of Category C agents include:

  • Nipah virus
  • hantavirus

Critical Priorities
Recognition of?response to and risk communication about bioterrorism threats must remain critical priorities for the public health community as it seeks to optimize the nation?s preparedness level.

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