The use of pathogenic microorganisms as weapons is not a science-fiction scenario. Throughout history, there have been documented military biological weapons programs, as well as confirmed cases involving the deliberate spread of infectious agents.

What Are Biological Warfare and Bioterrorism?

According to the World Health Organization (WHO), biological weapons include microorganisms such as bacteria, viruses, and fungi, as well as toxic substances of biological origin, that are deliberately used to cause disease or death in humans, animals, or plants. [1]

It is important to note that biological warfare and bioterrorism are not synonymous and have different meanings.

Biological warfare refers to the use of biological weapons in the context of military operations.

In contrast, bioterrorism refers to the deliberate use or release of biological agents for terrorist purposes — that is, to cause fear, exert political pressure, or inflict harm on a population.

Which Microorganisms Can Be Used as Biological Weapons?

Not all pathogenic microorganisms pose the same level of threat.

The CDC has developed a classification system for potential bioterrorism agents based on characteristics such as disease severity, potential for dissemination, and consequences for public health.

Category A agents include, among others:

  • Bacillus anthracis: The bacterium that causes anthrax.
  • Yersinia pestis: The bacterium that causes plague.
  • Variola virus: The virus that causes smallpox.
  • Clostridium botulinum: A bacterium that produces botulinum toxin.
  • Francisella tularensis: The bacterium that causes tularemia.
  • Certain viral hemorrhagic fever viruses, including Ebola and Marburg viruses. [2]

However, not all of these agents can be transmitted from person to person.

For example, anthrax is not usually transmitted between people, whereas pneumonic plague can spread through respiratory droplets under certain conditions. Biological toxins also do not replicate within the body in the way that infectious microorganisms do.

Have Biological Weapons Been Used in the Past?

Historically, there have been documented cases involving both the military use of biological weapons and acts of bioterrorism.

1. Japan and Unit 731 (World War II)

During World War II, the Imperial Japanese Army developed a biological weapons program in which the notorious Unit 731 played a central role.

As part of this program, inhumane experiments were conducted on prisoners, and the use of pathogenic agents against populations in China was also documented.

The program included research involving bacteria such as Yersinia pestis and Bacillus anthracis. It represents one of the most extensively documented historical examples of the organized development and use of biological weapons. [3]

2. Salmonella Attack (United States, 1984)

In 1984, in The Dalles, Oregon, members of a religious community deliberately contaminated food in restaurants with Salmonella Typhimurium.

In total, at least 751 people became ill.

The initial epidemiological investigation identified an association between the cases and specific restaurants. The deliberate contamination was later uncovered through a criminal investigation.

The incident is a well-known example of bioterrorism and was analyzed in a scientific publication in JAMA. [4]

3. Anthrax Letters (United States, 2001)

Shortly after the terrorist attacks of September 11, 2001, letters containing spores of Bacillus anthracis were mailed to U.S. media organizations and political figures.

According to the CDC’s epidemiological investigation, 22 cases of anthrax and five deaths were recorded.

The incident highlighted the importance of cooperation between laboratories, health authorities, and law-enforcement agencies in identifying and responding to a biological attack. [5]

Are Biological Weapons Prohibited?

Yes. The prohibition of biological weapons is established under international law.

The 1925 Geneva Protocol prohibited the use of bacteriological methods of warfare. However, it did not comprehensively prohibit the development and possession of biological weapons.

It was followed by the Biological Weapons Convention (BWC), which opened for signature in 1972 and entered into force on March 26, 1975.

The Convention prohibits the development, production, acquisition, and retention of biological weapons and requires the destruction of prohibited stockpiles. [6]

However, although states that are parties to the Convention have committed not to develop or possess biological weapons, there is no comprehensive international mechanism that systematically verifies whether they are complying with this commitment.

The issue remains the subject of international discussion and research proposals aimed at strengthening transparency. [7]

How Can We Determine Whether an Outbreak Is the Result of a Biological Attack?

One of the major challenges facing scientists and authorities is that a deliberate biological attack may initially resemble a naturally occurring outbreak.

An investigation may involve epidemiological surveillance, laboratory testing, analysis of the characteristics and distribution of cases, and cooperation with the relevant authorities.

The appearance of unusual epidemiological patterns may prompt further investigation, but it is not, by itself, evidence that a pathogen was deliberately released.

Establishing that such an event occurred requires additional scientific evidence and, where appropriate, forensic evidence.

The World Health Organization emphasizes that responding to a suspected deliberate biological event requires coordination among healthcare services, laboratories, public health authorities and security agencies. [8]

How Real Is the Threat Today?

The possibility of the deliberate use of biological agents remains an issue of international security and public health. However, this does not mean that every new outbreak or laboratory accident is evidence of bioterrorism.

At the same time, advances in biotechnology are creating new opportunities for the diagnosis, prevention, and treatment of disease, while also raising concerns about the potential malicious use of scientific knowledge.

This issue is described as dual-use research.

In 2022, the WHO published a dedicated guidance framework for the responsible use of the life sciences and the management of biological risks. [9]

Effective protection does not rely solely on banning biological weapons. It also depends on strengthening public health systems, laboratory biosafety and biosecurity, epidemiological surveillance and international cooperation.