Biological agents
Overview
The threat from biological agents arises when naturally occurring microbes are weaponized—harnessed and modified to cause disease or even kill many people. Organisms can be used in their naturally occurring state, or they may be able to be modified to increase virulence and/or render the disease they cause resistant to treatment.
To determine if an outbreak may be bioterrorism, scientists will look for the following characteristics:
- A large number of cases appearing at the same time, particularly in a discrete population (e.g., people from the same town, people who attended the same event)
- A large number of cases of a rare disease or one considered a bioterrorism threat (e.g., plague, tularemia)
- More severe disease manifestation than typical for a given disease and/or an unusual route of exposure
- A disease that is unusual in a given place or is out of season (e.g., a flu outbreak in the summer in the United States)
- Multiple simultaneous outbreaks of the same disease or different diseases
- A disease that affects animals as well as humans
- Unusual disease strains or uncommon antibiotic resistance to an organism
Although some of these characteristics may be true of a naturally occurring outbreak, they will generally signal that the outbreak needs to be closely scrutinized.
Understanding biological agents
The first step in understanding biological agents and how they affect the human body is a review of associated terminology.
Infectious Diseases
- Infectious diseases are caused by the invasion of the body by harmful microorganisms.
- Microorganisms multiply and make the person sick by attacking organs or cells in the body.
- These harmful microorganisms include viruses and bacteria, as well as certain other microscopic organisms, and are sometimes called pathogens.
- There is usually a lag time, called an incubation period, between when a person is infected and when the symptoms appear.
- People can become infected with these diseases in any number of ways, including consuming contaminated water or food, being bitten by insects or animals, or inhaling or touching the microorganisms or their spores.
Spores are produced by certain bacteria and plants. Like seeds, spores do not grow until the environment is conducive for them to do so. They are highly resistant to heat and other environmental factors. - All of the diseases discussed in this section are considered infectious diseases. Illnesses caused by chemical agents, by contrast, are not infectious diseases.
Contagious Diseases
- A contagious disease is an infectious disease that can be caught by a person who comes into contact with someone who is infected. Not all infectious diseases are contagious.
- Exposure to a contagious disease usually happens through contact with the infected person's bodily fluids or secretions, such as a sneeze.
- Depending on the disease, the level of contact required to pass on the illness could be as casual as water droplets in the air from a cough (e.g., smallpox).
- The level of contagiousness has nothing to do with how serious the resulting disease may be. For example, pneumonic plague and the common cold are both highly contagious, but pneumonic plague is obviously a much more serious disease.
- There are some infectious diseases that are not contagious at all, no matter how close the contact with an infected person (e.g., botulism, tularemia).
Toxins
- Toxins are the poisonous, usually protein-based, substances produced by microorganisms (bacteria, mold, virus) in certain infectious diseases.
- Microorganisms use these toxins as the specific weapons for attacking organs or cells in the body.
- Antitoxins are medications that attempt to neutralize a toxin without necessarily killing the bacteria, mold, or virus that is producing the toxin.
- Many different types of antitoxins exist, because a specific antitoxin will usually only fight a particular kind of toxin.
- Although toxins are usually classified as being biologically produced, common language often refers to the poisons created by nonliving chemical agents as chemical toxins.
- Although some of these characteristics may be true of a naturally occurring outbreak, they will generally signal that the outbreak needs to be closely scrutinized.
Bacteria and Viruses
Both bacteria and viruses can cause infectious diseases.
Bacteria:
- Bacteria are one-celled microorganisms that are capable of multiplying.
- Not all bacteria are harmful (e.g., bacteria turn milk into cheese).
- Antibiotics are medications that can be used to kill harmful bacteria.
- Some bacteria can develop resistance to antibiotics, making the medications less effective.
- Hospitals will typically have supplies of antibiotics known to be effective against most Category A and B bacterial agents.
Viruses:
- Viruses are simpler than bacteria, often made up merely of a bit of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) that is surrounded by a protective coat of protein.
- Viruses are parasitic in nature and unable to multiply without host cells—cells within a person's body that the viruses invade and use to multiply.
- Antibiotics are not effective against viruses.
- Some antiviral medications do exist, but many that might help against Category A agents are still in clinical trials. Consult HHS's National Institutes of Health's National Institute for Allergy and Infectious Diseases' (NIAID) Web site for ongoing research in this area.
Delivery of biological agents
The ability to successfully deliver a biological attack depends on:
- The type of agent or organism
- The method of dissemination
- The weather (e.g., wind speed, humidity, time of day, precipitation, temperature):
Wind speed affects how widely an agent can be spread
Humidity can cause decomposition of an agent
Precipitation can cause clumping, making fine particles more difficult to inhale
Routes of Entry
Biological agents can enter the body through:
- Absorption
- Inhalation
- Ingestion
- Injection
Delivery Methods
Biological weapons can be prepared for delivery as a weapon in wet or dry form:
- In dry form, agents are more stable and refinement is easier.
- In liquid form, agents are less stable, require refrigeration, and are difficult to refine to small particle sizes.
Biological weapons can be delivered by:
- Wet or dry aerosol sprayers
- Explosive devices
- Transmission through insects, animals, or humans
- Introduction into food, water, or even medications
- In or on objects, in some cases (e.g., anthrax in envelopes)
Effectiveness of Release
The effectiveness of a biological release depends on:
- The particle size and its potency (for example, in an aerosol release, the size must be between 1 and 5 microns to be inhaled and cause illness). (Note: 1 micron is one millionth of a meter. A strand of hair ranges between 20 and 200 microns in width.)
- How well the agent survives in the environment
- Weather conditions
Testing for biological agents
Quick diagnosis and treatment of a patient exposed to a biological agent are key to saving that patient's life. A biological attack may go unnoticed until large groups of people begin exhibiting symptoms, which makes prompt diagnosis even more critical. But getting a quick medical answer is complicated by the fact that currently there is no single test that can diagnose whether a person has been exposed to biological agents. There are clinical trials underway, however, on better testing methods.
To look for evidence of biological agents, physicians will take blood or other samples to be tested at clinical laboratories. As the clock is ticking, the sample must be collected and sent to the appropriate lab for analysis. However, it takes time to isolate the bacteria, toxin, or virus from the sample. This time frame can stretch from hours to days, depending on the agent, the amount of exposure, the proximity and capabilities of the lab, and the time the test(s) take. The following list provides descriptions of the types of tests that may be run:
Environmental testing is examining a building or an area for the presence of a biological or chemical agent. Testing is usually a two-step process. Using anthrax as an example, if the sample contains a large amount of the bacteria (Bacillus anthracis), a positive reading may come back within minutes. However, this quick initial result from the scene may be what is called a false positive result, so a more reliable test must be done by a more sophisticated laboratory to confirm the results. The confirmation test can take up to 72 hours depending on how fast the bacteria grow and can be positively identified.
A nasal swab is an environmental test that may be used to assist in a public-health investigation to determine the presence of a bioterrorism agent in an area or building. Nasal swabs are not used to determine if a person is infected by a given agent.
A culture is a method for growing an organism in the lab (for example, in a petri dish). A culture can help in identifying a bacteria or virus. Cultures are the most readily available technology for clinical diagnosis of a suspected case of bioterrorism but can be time consuming to complete.
A blood culture is a test that looks for bacteria or viruses in the blood. Blood is drawn from a patient, and the sample is sent to a special laboratory for analysis. The sample is incubated, or kept in a warm place, at a certain temperature, and in this controlled environment, the bacteria grow and are isolated from the blood for easier identification.
"Media" are the nutrient mixes used to grow organisms in a lab. Selective media are used to identify an organism by giving it or depriving it of certain nutrients. For example, selective agents can be added or removed, which "poison" some organisms while allowing others to grow.
Gram staining uses dyes to make a bacterial cell stand out for identification. A specimen is put on a slide, and a four-part staining procedure begins. This test may produce results in less than an hour, but it is not specific enough to definitely identify the organism, and a longer confirmation test is still needed.
Obtaining sputum involves getting a sample of a patient's phlegm by having him or her cough it up. Sputum samples are usually ordered when a patient is exhibiting pneumonialike symptoms that could be an indicator of an inhalational form of anthrax, plague, or tularemia. The sample is then stained and viewed under a microscope to look for the presence of certain bacteria. Part of the same sample is also used for a culture.
There are also more sophisticated tests that are used to identify agents, such as:
Immunoassays, which look for specific antigens or antibodies and are useful in detecting the presence of toxins. However, antibody production for identification can take time.
Gene amplification assays, such as a polymerase chain reaction, which look at the DNA or RNA to identify an agent. However, sample preparation can take a long time.
In general, detection and identification using any of these methods is dependent on the sample quantity and quality and the exactness of the processing. A combination of tests will yield the most accurate results. In the absence of immediate results, physicians who suspect bioterrorism may begin a preliminary course of treatment until the lab results are in.
How long testing should take
Unfortunately, there is no single answer to the question of how long testing will take. The testing of biological agents is complicated by several factors, which can affect the time that passes before the presence of an agent can be confirmed or a diagnosis can be made. These factors include:
Identifying the agent.Although bioterrorism is now a household term, actual incidents of bioterrorism have been rare, leaving today's physicians with limited experience in identifying these agents in the lab or treating affected patients. This means that the first patients who become sick may be mistaken for having other illnesses, thus causing a delay in the effort to test for biological agents.
Presumptive vs. confirmatory diagnoses. Not all tests are conclusive. Some tests, such as Gram stains, can give a presumptive diagnosis that an agent is present, but follow-up tests are needed. In general, presumptive diagnosis of an agent can usually be made in about a day. Confirmatory diagnosis can take two to three days.
Viral, bacterial, or toxin load. The "load" refers to how much of the agent is present in a patient. If relatively large amounts of an agent are present in a patient, cultures designed to grow the bacteria or virus could take as little as a few hours. If smaller amounts of the agent are present in a patient, these same culture tests could take up to two or three days.
Lab capabilities. Can the needed tests be done in local labs, near a suspected attack, or do the samples need to be shipped out to more advanced labs, thus affecting the overall timeline? Shipping samples to more advanced labs can tack on an extra day or two to the wait time. CDC's Laboratory Response Network helps facilitate this process.
The kind of test that is used. Numerous tests are employed to detect the presence of bioterrorism agents. Blood cultures can take up to three days in some cases, for example, but Gram stains can be ready within an hour. However, some of these quicker tests will only give preliminary information, which must be confirmed with more comprehensive tests.
What we don't know about biological weapons of mass destruction
- It is not known who is in possession of biological weapons of mass destruction.
- Medical experts do not know if bacteria have been engineered to be resistant to antibiotics.
- Experts do not know how potent the strains will be in a biological attack.
- Experts do not know if the illnesses caused by some of these agents will be immediately recognizable.
- There is disagreement on how long some of these agents can survive in the environment.
- Experts do not know if the diseases these agents cause will be the same as past epidemics (e.g., is today's smallpox the same as the disease that was eradicated?).
More information on disasters and emergencies is available at the U.S. Department of Health and Human Service's website: http://www.hhs.gov/emergency