salmonella1a (320x240)
credit: NIAIDSalmonella bacteria, a common cause of foodborne disease, invade an immune cell.

Bioterrorism agents are pathogenic organisms or biological toxins that are used to produce death and disease in humans, animals, or plants for terrorist purposes. These agents are typically microorganisms found in nature, but it is possible that they could be modified to increase their virulence, make them resistant to current antibiotics or vaccines, or to enhance the ability of these agents to be disseminated into the environment.

Terrorists may find biological agents to be an attractive alternative to conventional weapons because of their relatively low costs, their relative accessibility, and the relative ease in which they could be produced, delivered, and avoid detection. Their use, or even threatened use, is potentially capable of producing widespread social disruption.

The concept of using biological agents in warfare is not new. There are many examples throughout recorded history - even as early as the 6th century BC when the Assyrians reportedly poisoned wells of their enemies with the fungus rye ergot. In the 1700s during the French-Indian War, it is suspected that the British gave blankets that had been used by smallpox victims to the Native Americans, resulting in decimation of the native population. More recently, in 1984, followers of the Bhagwan Shree Rajneesh contaminated salad bars in Oregon with Salmonella in an attempt to influence a local election (although hundreds were sickened, this attack did not impact the election). However, as our knowledge of infectious disease agents increases, and the technology to design and produce these agents improves, there is an elevated risk that biological agents could used as weapons of mass destruction in the future.

As a result of the terrorist attacks in New York City and Washington, D.C on Sept. 11, 2001 and the dissemination of anthrax through the United States Postal Service shortly thereafter, there has been renewed and urgent attention focused on the possibility of additional terrorist acts involving biological agents. The U.S. government has responded by greatly expanding resources and effort into biodefense research. More than $4 billion has been requested by the president for the 2006 budget for biodefense at the Department of Health and Human Services. Much of this money is targeted to the National Institute of Allergy and Infectious Diseases component of the National Institutes of Health and the Centers for Disease Control and Prevention. These agencies have set research priorities based on a classification system developed by the CDC to categorize the threat of potential agents for use in bioterrorism.

Classification of Bioterrorism Agents

Potential bioterrorism agents are classified into Categories A, B, and C based on

  • their ability to be disseminated
  • their mortality rates
  • actions required for public health preparedness
  • their capability of causing public panic

Category A agents are considered the highest risk agents, and much of the biodefense research effort is directed at these agents. Category C includes agents that are considered emerging infectious disease threats.

Definition of Potential Bioterrorism Agent Categories

Category A

Category B

Category C

Pose the highest risk to national security

Pose the second highest risk to national security

Emerging pathogens that could be engineered for mass dissemination

Can be easily disseminated or transmitted from person to person

Are moderately easy to disseminate

Are easily produced and disseminated

Result in high mortality rates

Result in low mortality rates

Have potential for high mortality rates

Require special preparedness actions

Require enhancement of diagnostic and surveillance capability

Are available

Have potential to cause public panic and social disruption

Examples of Potential Bioterrorism Agents by Category

Category A

Category B

Category C





Diarrheagenic E. Coli



Hepatitis A



Ricin toxin

Multi-drug resistant tuberculosis



Yellow fever

Viral hemorrhagic fevers (e.g. Ebola, Marburg, Dengue)

West Nile Virus


Biodefense Research

Research efforts in biodefense are directed at

  • understanding the basic biology of potential bioterrorism agents
  • understanding the interaction between the human immune system and these microorganisms
  • developing and improving drugs and vaccines that are effective against bioterrorism agents
  • developing tools to quickly and accurately diagnose diseases caused by these agents
  • establishing resources and biosafety laboratories to facilitate biodefense research.

Research at Baylor College of Medicine

cdc anthrax 1 (320x240)
credit: CDC / Janice CarrElectron microscope image of Bacillus anthracis spores.

In the Department of Molecular Virology and Microbiology at Baylor College of Medicine, research is being conducted on several Category A agents - anthrax, dengueEbola, smallpox, and tularemia. Work is also ongoing on the Category B and C agents - noroviruses, influenza, SARS and MERS, and tuberculosis. The research encompasses investigations into the basic biology of these agents, their interactions with the immune system, as well as the development of vaccines and tools to study and combat these agents.

Notably, MVM is home to a Vaccine and Treatment Evaluation Unit (VTEU), one of only seven such sites nationwide. The VTEU is funded by the NIAID component of the NIH and provides the infrastructure to conduct phase I and II clinical trials of candidate vaccines and other biologics for protection against biological weapons and emerging infectious diseases. This unit conducts detailed laboratory investigations of human immune responses to vaccination and epidemiologic and laboratory surveillance for infectious diseases to provide background information for clinical trials. The BCM VTEU has been evaluating vaccines for anthrax, smallpox, and tularemia and conducting clinical trials for vaccines for the prevention of influenza and SARS.