Module 2:

How Biological Weapons Work

1. How are biological weapons developed and tested?

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How are biological weapons developed and tested?

2. How difficult is it for states to acquire biological weapons?

  • Given the dual-use nature of biotechnology, most countries with pharmaceutical and medical industries have the technical capability to produce biological weapons. The global explosion of the biotechnology and pharmaceutical industries will increase the number of countries with this potential.
  • Some analysts argue that tacit knowledge―the experience gained only through past hands-on experience with biological agents―is a tremendous asset, without which it can be difficult to launch a biological weapons program. [1] However, advances in biotechnology have increased automation of certain procedures, reducing scientific training requirements.
  • Developing an effective BW agent delivery system, such as cluster munitions, can be extremely difficult. This is particularly true when the agent selected for dissemination is not naturally resilient to environmental and physical stresses.

3. How are biological weapons delivered to a target?


1. Introduction

Biological weapons target living things such as people, livestock, or crops. Biological weapons might be used to assassinate individuals or attack enemy troops or civilian populations. While there are a host of potential methods to deliver biological weapons, their complexity and effectiveness vary widely. The least complex systems are less likely to fail, but their capabilities to disperse agents widely are usually limited.

Drawings: Biological weapon collage | Credit: Aly Minamide, Intern, Center for Nonproliferation Studies


2. Natural Sources of Disease

Before it was widely understood that microorganisms caused disease, infected corpses or contagious individuals were used to spread disease during warfare. In the Middle Ages, people believed that diseases were caused by “miasma” or contaminated air. During the siege of Caffa in 1347, the Tartar army catapulted bodies over the city walls, hoping that the unbearable smell would poison its inhabitants.

Source: Mark Wheelis, “Biological Warfare at the 1346 Siege of Caffa,” Emerging Infectious Diseases, Volume 8, No. 9 (2002).
Drawing: Mosquito | Credit: Aly Minamide, Intern, Center for Nonproliferation Studies

Woman Coughing

2. Natural Sources of Disease Cont.

Military forces understood that dead bodies and other contaminated objects, such as blankets used by individuals infected with smallpox, were effective sources of disease, although they did not understand why. Their tactics to spread disease depended on fomites (physical objects that can carry bacteria and other infectious agents—such as contaminated blankets), or vectors (living organisms such as humans or insects that can carry the disease).

Drawing: Woman coughing | Credit: Aly Minamide, Intern, Center for Nonproliferation Studies


3. Applied Microbiology

As scientists gained a better understanding of the origin of diseases and how they spread, governments began to seriously consider producing and employing pathogens as weapons. Yet while military microbiologists learned to produce agents in much larger quantities, delivery systems remained fairly primitive through WWII. Japan’s wartime attacks still relied on methods such as fomites, vectors, and contaminating food and water sources.

Source: Gregory Koblentz, Living Weapons, (New York, NY: Cornell University Press, 2009), p. 12.
Drawing: Microbiologist | Credit: Aly Minamide, Intern, Center for Nonproliferation Studies


3. Applied Microbiology Cont.

For example, from 1932 to 1945, Japan bred fleas infected with Y. pestis (plague) in large numbers and developed porcelain bombs to deliver them. Although Japan was the only country known to have carried out large-scale attacks during this period, others were exploring munitions that could disseminate agents more widely.

Source: “Technical Aspects of Biological Weapons Proliferation,” in Office of Technology Assessment, Technologies Underlying Weapons of Mass Destruction, OTA-BP-ISC-115 (Washington, DC: U.S. Government Printing Office, December 1993), p. 94.
Drawing: Airplane dropping a bomb | Credit: Aly Minamide, Intern, Center for Nonproliferation Studies

Airplane Dusting BW

4. Industrial Microbiology and Aerobiology

Advances in the pharmaceutical, baking, and brewing industries eventually led to industrial-scale production of microorganisms, enabling states to produce more disease-causing organisms than ever before. Meanwhile, aerobiology, the study of the dispersion of airborne materials, had become a serious field of study, making the large-scale dissemination of pathogens in aerosol form possible. Iraqi forces, for example, were developing a variety of delivery systems available in the 1980s, including aircraft-dropped bombs and spray tanks containing biological agents.

Photo: Airplane dusting airborne materials | Credit: Aly Minamide, Intern, Center for Nonproliferation Studies

4. What are the effects of biological weapons?

  • The effects of biological weapons depend on the type, quality, and quantity of the agents employed, and the effectiveness of the delivery systems, as well as the conditions under which attacks are carried out. [2]
  • Some diseases, such as plague and smallpox, are contagious. Others, such as anthrax, do not spread person-to-person. [3]
  • The Centers for Disease Control (CDC) separates potential bioterrorism agents that cause infections in humans into three categories: A, B, and C. [4] There are also potential agents that cause infection in livestock or crops. Biological weapons can have a major effect not just in terms of physical casualties, but also in terms of social disruption, economic losses, and environmental damage.

Category A

  • Highly lethal
  • Potential for major public health impact; panic and social disruption
  • Easily disseminated, or capable of spreading person-to-person
Bacillus anthracis (anthrax)
Clostridium botulinum toxin (botulism)
Yersinia pestis (plague)
Variola major (tularemia)
Francisella tularensis (smallpox)
Ebola and other viral hemorrhagic fevers

Category B

  • Moderately easy to disseminate or transmit person-to-person
  • Moderate infection rates, but generally less lethal than Category A agents
Brucella species (brucellosis)
Coxiella burnetii (Q fever)
Ricin toxin
Vibrio cholerae (cholera)

Category C

  • Emerging pathogens that could be engineered in the future to be easily produced and disseminated and/or cause high mortality rates and major public health challenges
  • Defined by the likelihood that they could be weaponized in the future, so the list changes frequently
  • Sometimes includes pathogens that exhibit resistance to countermeasures
Emerging infectious diseases such as Nipah virus and hantavirus

5. Can biological weapons be stockpiled?

  • If properly maintained, biological weapons can be stored for decades.
  • Because biological warfare agents are living organisms, many will decay quickly if exposed to adverse environmental conditions. Unless an agent is to be used shortly after production, most agents will need to be stabilized in order to withstand the stresses of storage, transport, and dissemination.
  • Most stabilization methods involve freezing and/or dehydration in order to slow down agents’ metabolism. Many of these methods are widely used in the pharmaceutical industry and to produce a variety of commercial products.
  • Some microorganisms, such as Bacillus anthracis (anthrax), can naturally slow their metabolisms by forming dormant spores. This natural process can be emulated in a laboratory by applying a coat of protective material to certain pathogens and toxins through a stabilization method known as microencapsulation.
  • State-run programs traditionally stockpiled bioweapons to ensure their militaries could quickly access them if needed. The Soviet program, however, also maintained facilities that were capable of producing large agent quantities on demand. [4] Recent and future technological advances could enable ostensibly peaceful-use activities to be more readily converted to military use, facilitating smaller-scale, more controlled, on-demand production, and obviating the need for industrial-scale production, and extensive stockpiling. Such developments are likely to pose serious nonproliferation verification challenges.

6. Are there effective defenses or cures to counter biological weapons use?

There are measures that can mitigate the consequences of a biological attack. Many of these defenses are agent-specific. Most vaccines, for example, only work against one pathogen, and developing them is an expensive undertaking. However, a robust biodefense program combined with appropriate public health measures can help a country to minimize the effects of a biological attack. Key measures include:


  • Protective suits, shelters, clothing, and gas masks can defend individuals in the event of an attack and may also deter would-be attackers who realize they may not achieve their desired goals.
  • Protective measures are particularly useful for military personnel and first responders whose duties increase the likelihood of coming into contact with a pathogen or infected individuals.
  • Vaccines, when available, offer protection if administered prior to an attack.


  • The ability to detect and diagnose a biological attack or natural outbreak is critical to limiting the scale of its potential consequences, as it enables treatment of the infected and allows time for people who are not infected.
  • The international community has launched several initiatives to strengthen global health surveillance. However, many developing countries lack the resources or infrastructure to support the detection and diagnosis of even well-known diseases, nevermind emerging ones.
  • Detection systems can take a few hours to a few days to detect biological weapon exposure, and advances in biotechnology will likely increase their efficiency.

Medical Countermeasures

  • The use of antibiotics, antivirals, and antitoxins can improve infected individuals’ odds of survival.
  • Some infectious agents preclude the use of antibiotics or antivirals because such drugs do not exist or are in short supply, or because the agent has been manipulated to increase its resistance to countermeasures.
  • To be effective, medical countermeasures require a robust public healthcare system that can rapidly diagnose and administer the proper drugs—an asset that is lacking in many parts of the world.


  • Most biological agents do not live very long once disseminated. Some pathogens, such as Bacillus anthracis (anthrax) spores, are persistent and can contaminate areas for long periods of time.
  • Disinfection and decontamination methods typically rely on chemicals, heat, or UV light.


[1] See, for example, James Revill and Catherine Jefferson, “Tacit knowledge and the biological weapons regime,” Science and Public Policy (2014) 41 (5): 597-610; Kathleen Vogel, “Bioweapons Proliferation: Where Science Studies and Public Policy Collide,” Social Studies of Science (October 2006) vol. 36 (5): 659-690.
[2] Centers for Disease Control and Prevention, “Anthrax – Basic Information- How People are Infected,” September 1, 2015
[3] Centers for Disease Control and Prevention, “Bioterrorism Agents/Diseases,”
[4] Mark A. Prelas and Michael Peck, Nonproliferation Issues for Weapons of Mass Destruction, (Boca Raton, FL: CRC Press, 2005), p. 46.

Photo Credit
Header Image: Drills conducted in full chemical protective gear. Source: U.S. Navy via WikiMedia Commons.