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Terms and Definitions for Biological Agents Fact Sheets

Abscess: A localized collection of pus resulting from an infection.

Adjuvant: A substance that is added to a vaccine to improve the immune response so that less vaccine is needed. Aluminum hydroxide is the only FDA licensed adjuvant in the United States.

Aerosol, aerosolized: A suspension of small (< 5µm) particles or droplets in the air. Aerosolized biological agents may remain suspended in air for long periods and may travel long distances. Aerosol (or airborne) transmission occurs when an aerosol containing a biological agent is inhaled by and infects another person. Aerosols are generated naturally by coughing, sneezing, talking or breathing. Certain medical procedures, such as endotracheal intubation, mechanical ventilation, and airway suctioning, can generate aerosols. Aerosols also can be produced intentionally to deliver a biological weapon.

Airborne precautions: Airborne precautions are actions taken to prevent the transmission of infectious agents that are suspended in the air (aerosols) and that are therefore infectious over long distances.

Antibiotic susceptibility: The vulnerability of a specific bacterial strain to antibiotic treatment. Some bacterial strains are resistant to specific antibiotics, so antibiotic susceptibility must be determined before drugs are chosen for prophylaxis or treatment.

Antibodies: Proteins that are produced by specialized cells of the immune system, called B cells, after stimulation by an antigen. Antibodies (also called immunoglobulins) act specifically against the antigen in an immune response.

Avirulent: Not virulent. A biological agent is avirulent when it does not cause disease.

Biovar: Formerly called a biotype, a biovar is group of bacterial strains distinguishable from other strains of the same species on the basis of physiological characteristics.

BSL-3: Biosafety level 3. A level of laboratory precaution suitable for work with most pathogens transmitted through inhalation.

BSL-4: Biosafety Level 4. This level is required for work with the most dangerous (highly lethal) agents that pose a high risk of aerosol transmission. Examples of agents requiring this level are the Ebola virus and variola (the smallpox virus).

Cyanosis: A bluish discoloration of the skin due to inadequately oxygenated blood.

Epidemic: A sudden outbreak of disease within a population that produces greater numbers of cases of disease during a given time period than would typically be expected.

Endemic: A disease that is constantly present to a greater or lesser degree in a human population in a specific geographic location. Enzootic is the comparable term referring to diseases associated with animal populations.

Immunogenic: Relating to or producing an immune response.

Incubation period: The time from infection to the appearance of symptoms in infected persons.

Infectious dose: The amount of pathogen (measured in numbers of organisms) required to cause infection in the host.

Inoculation: The introduction of a substance into a body in order to induce an immune response.

Isolated, isolation, and quarantine: Public health measures that are implemented to stop the spread of communicable disease. Isolation refers to the separation and restriction of movement of people who are sick with an infectious illness from those who are not infected. Quarantine refers to the separation and restriction of movement of persons who are not currently sick but have been exposed to an infectious agent and may become sick and/or spread illness to others. In most cases, isolation and quarantine are voluntary. However, federal, state, and local governments do have the authority to enforce the isolation and quarantine of those who are sick and those who are suspected of being exposed to an infectious disease.

Morbidity: The incidence of disease; the rate of sickness.

Mortality: The number of deaths in a given time or place; the proportion of deaths to population.

Negative pressure isolation room: A hospital room, generally used with tuberculosis patients, that isolates infected patients and is designed to direct air flow from outside corridors and rooms into the room, preventing the chance for contaminated air to flow to other parts of a building.

Nephritis: Inflammation of the kidney caused by infection, a degenerative process, or vascular disease..

Of concern: Biological agents that have specific characteristics—including high infectious properties, easy person-to-person transmission, lack of countermeasures, and easy weaponization or aerosolization—that qualify them as high priority threats, or biological agents “of concern.”

Pandemic: A widespread epidemic that affects populations on different continents and that possibly circulates around the world.

Parenteral: The administration of medication through intravenous, intramuscular, or subcutaneous injection.

Percutaneous: Through the skin.

Phase I clinical trial: The first stage of testing unlicensed drugs and vaccines in humans. Phase I studies are designed to determine the metabolic and pharmacologic actions of a drug in humans, the side effects associated with increasing the doses, and, if possible, to gain early evidence of effectiveness. Phase 1 studies also evaluate drug metabolism, structure-activity relationships, and the mechanism of action in humans.

Phase II clinical trial: Controlled clinical studies that are conducted to evaluate the effectiveness of a drug for a particular indication(s) in patients with the disease or condition under study, and to determine the common short-term side effects and risks.

Phase III clinical trial: Expanded controlled and uncontrolled studies that are conducted following the collection of preliminary evidence suggesting effectiveness of a drug. Phase III clinical trials are intended to gather additional information to evaluate the overall risk-versus-benefit relationship of a drug, and to provide an adequate basis for physician labeling.

Phase IV clinical trial: Postmarketing studies conducted to obtain additional information about a drug such as its risks, benefits, and optimal use.

Pleural effusion: An accumulation of fluid in the space surrounding the lungs.

Postexposure prophylaxis: Administration of a therapeutic agent (usually a drug) after exposure to a pathogen in order to reduce the likelihood of illness.

Preclinical trial: Experimental testing of drugs in test tubes or animals. These trials are conducted before testing in humans.

Respiratory droplet transmission: Droplet transmission occurs when relatively large particles (>5 microns) containing a biological agent are propelled from an infected person over relatively short distances (3-6 feet) and deposited onto the mucous membranes (usually mouth or nose) of another person or onto an environmental surface.

Respiratory droplet precautions: The use of gowns, gloves, eye protection, and surgical masks to protect against respiratory droplets.

Septic shock: A condition in which an infection initiates a complex cascade of physiological effects that can result in inadequate blood pressure, organ failure, and death.

Standard precautions: Protective actions that are taken in a healthcare setting (such as the use of gowns and gloves) to prevent skin and mucous membrane exposure when contact with blood or other body fluids is anticipated. Standard precaution guidelines are based on the principle that all blood, body fluids, secretions, nonintact skin, mucous membranes, and excretions (except sweat) may contain transmissible infectious agents.

Subcutaneous: Under the skin.

Supportive therapy: A medical treatment that relieves symptoms or maintains basic functioning, but which is not specific to the underlying disease. Examples include intravenous fluids, pain medication, oxygen, fever control, and nutrition.

Surveillance and containment: This refers to the detection of disease cases through various reporting mechanisms and, in the case of smallpox and other communicable diseases, the isolation of infected individuals and vaccination of potentially exposed persons.

Tachycardia: Relatively rapid heartbeat.

Tachypnea: Increased rate of respiration.

Virion: A complete virus particle, including genetic material and protein coat, as it would exist outside of a cell.

Virulent: A biological agent is virulent when it has the ability to overcome the host’s immune defenses and cause disease. Virulence is a measure of the severity of disease that an agent is capable of causing.

Weaponized: In the context of biological weapons, ‘weaponization’ refers to the act of adapting a biological agent for use as a weapon. When a biological agent is referred to as having been weaponized, it usually means that it has been manipulated or treated in such a way as to improve its effectiveness as a weapon by making it more virulent, more easily disseminated as an aerosol, or more stable.

Zoonosis, zoonotic disease: A disease that can be spread from wild or domesticated animals to humans. Examples of zoonotic diseases include anthrax, plague, and tularemia. Much of the world’s emerging infectious diseases are zoonotic.