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Bioterrorism Agents

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Also known as: Biological Warfare

What are bioterrorism agents?

Bioterrorism agents are materials, such as bacteria, viruses, fungi, or toxins, that are deliberately used to sicken and kill. They may be used by terrorists partially because of their psychological impact on the public and partially because they can be deadly, are easy to distribute, and are difficult to detect. Bioterrorism agents have been used in acts of warfare for thousands of years. This has included dipping arrows into toxins, poisoning food and water supplies, and deliberately spreading deadly infections. Bioterrorism agents could be carried in food products, dispersed into the air or drinking water, or introduced into crops and livestock, or even sent through the mail as was done in 2001.

Most potential bioterrorism agents are natural substances or microorganisms that normally cause a small number of deaths each year and/or during periodic outbreaks. They enter the body primarily by being inhaled into the lungs, ingested, or may enter through breaks in the skin or through contact with the mucous membranes of the eyes and nose. Agents may be altered by those seeking to use them as a weapon; they may be concentrated, made easier to disperse (aerosolized), made more likely to infect, and/or made more resistant to treatment. Some agents cause infections that can be passed easily from person-to-person and would need to be quickly contained, while others, such as anthrax, typically affect only the person exposed but can be deadly without prompt treatment.

The Centers for Disease Control and Prevention (CDC) categorizes bioterrorism agents according to the risk they pose to the public. Those that pose the highest risk, because they can be easily disseminated and could result in high mortality, are classified as Category A. The CDC classifies biological agents that pose a moderate risk to the public as Category B. These agents can be spread with some ease and can cause a moderate degree of illness, but death rates due to these diseases are usually low. Category C agents include emerging pathogens that warrant monitoring because they could be manipulated and used as a weapon, are easily available, and have the potential to make a big impact.

Examples of categories for select agents that the CDC has defined are included in the table below.

Category Disease Agent Agent Type
A Anthrax Bacillus anthracis Bacterium
A Botulism Clostridium botulinum toxin Bacterial toxin
A Plague, Pneumonic Yersinia pestis Bacterium
A Smallpox Variola major Virus
A Tularemia Francisella tularensis Bacterium
A Viral Hemorrhagic Fevers Arenaviruses (Lassa, Machupo)
Bunyaviruses (Congo-Crimean, Rift Valley)
Filoviruses (Ebola, Marburg)
B Brucellosis Brucella species Bacteria
B Q-Fever Coxiella burnetii Bacterium
B Psittacosis Chlamydia psittaci Bacterium
B Typhus Rickettsia prowazekii Bacterium
B Food Safety Threats Salmonella
Escherichia coli 0157:H7
B Glanders Burkholderia mallei Bacterium
B Melioidosis Burkholderia pseudomallei Bacterium
B Water Safety Threats

Cryptosporidium parvum

Vibrio cholerae



B Ricin Toxin From Ricinus communis Toxin from Castor Beans
B Viral Encephalitis Eastern equine encephalitis
Western equine encephalitis
Venezuelan equine encephalitis

For more specific information on agents of bioterrorism and emergency preparedness plans the U.S. government has in place in the event of another bioterrorist attack, visit the CDC's bioterrorism web site

In addition to biological agents, chemical or radioactive agents may also be used as weapons of bioterrorism. The CDC classifies chemical agents according to their target activity on the skin, in the lungs, in the digestive tract, and in the nervous system. An example of the use of chemical agents by a terrorist group occurred in 1994 and 1995 when the Aum Shinrikyo cult released the nerve gas sarin into the air in Matsumoto and Tokyo, Japan, resulting in 19 deaths and thousands of people requiring hospitalization or outpatient treatment.

Radioactive agents are colorless, odorless, and invisible to the eye. Contamination of food, water or objects may disable or kill humans and animals and can be difficult to trace. Symptoms of radiation exposure include nausea, vomiting, diarrhea and, depending on the extent of the exposure, bleeding gums, nosebleeds, bruising, and hair loss. Exposure to radioactive agents can be through ingestion, inhalation, or contamination of an open wound. An example of a radioactive agent is polonium 210 which, in 2006, was the cause of death of Russian dissident Alexander Litvinenko.

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