Biological agents are organisms or toxins that can cause deadly diseases in people, livestock and crops. The agents kill by spreading a disease that is normally fatal or by tricking the body's cells into producing a toxin that overwhelms its defenses. Only a small number of the hundreds of bacteria and viruses are viable as terrorist weapons because most cannot survive outside narrow temperature ranges or are too rare and hard to grow. There are different types of biological agents, including bacteria, viruses and toxins.

Biological agents can be handled easily and can cause great harm in small amounts. Drying the germs for use in a delivery system, such as an aerosol, is the most difficult part. The diminutive size of biological agents, five microns or less than one-fifth the width of human hair, means they can remain airborne for hours or, in still, dry weather, a day or more. Once inhaled, their size enables them to bypass the filtering mechanism in the upper respiratory system and enter the lungs and the bloodstream. It usually takes several days or weeks before the effects of biological agents become obvious.

Because biological agents cannot necessarily be detected and may take time to grow and cause a disease, it is almost impossible to know when an attack has occurred. The delayed onset of symptoms also creates potential for wider dissemination of the agent by infected people. If government officials become aware of a biological attack, they would most likely instruct residents to either seek shelter where they are and seal the premises or evacuate immediately. (Read more about Pandemic Threats.)

In this section, we discuss anthrax, smallpox, botulism, plague and tularemia.

The information in the introduction to biological agents was compiled from:
Chemical/Biological/Radiological Incident Handbook
Federal Emergency Management Agency
Weapons of Mass Destruction

Anthrax is a potentially fatal infection caused by bacteria called Bacillus anthracis. The bacteria occur mostly in warm-blooded animals, but it can also infect humans. Naturally occurring anthrax spores live in the soil throughout Asia, Africa and Great Britain and in U.S. locations such as Texas, Oklahoma and the Mississippi Valley. Spores can survive in adverse conditions and still remain capable of causing disease. Research on anthrax as a biological weapon began more than 80 years ago. Today, at least 17 nations are believed to have offensive biological weapons programs; it is uncertain how many are working with anthrax.

The three types of anthrax infections are cutaneous anthrax, gastrointestinal anthrax and inhalation anthrax - the most deadly. People can be infected with anthrax through skin contact, by drinking contaminated water, eating contaminated meat, or by inhaling the bacteria or spores.

The CDC states that there are no scientifically proven recommendations for preventing exposure from the mail. However, there are some commonsense steps people can take, such as not opening suspicious mail, keeping mail away from the face when opening, not blowing or sniffing mail contents, avoiding vigorous handling of mail, such as tearing or shredding, and washing hands after handling mail. Anthrax is generally not transmitted from person to person.

If contact with anthrax is suspected, health officials recommend isolating the area where the exposure is believed to have occurred, removing garments that may have had contact with the bacteria, washing any potentially contaminated body parts with soap and water, and contacting law enforcement officials immediately.

Early antibiotic use is essential -- a delay even in hours may lessen the chances for survival. For those treated with antibiotics, the risk of recurrence remains for at least 60 days. Doctors can prescribe effective antibiotics. Penicillin, tetracycline, erythromycin, cloramfenicol, doxycyclin and ciprofloxacin, known as Cipro, are some of those approved treatments.

A human vaccine for anthrax was first developed in 1954. There are limited supplies of a human vaccine for anthrax, and it is generally limited for military personnel, hospital and public safety workers.

Symptoms of the disease vary depending on how the disease was contracted but usually occur within seven days. Cutaneous anthrax could result in lesions, black ulcers, headaches, muscle aches, fever and vomiting. Symptoms of gastrointestinal anthrax include nausea, loss of appetite, vomiting and fever followed by abdominal pain, vomiting of blood and severe diarrhea. Initial symptoms of inhalation anthrax may resemble the common cold or flu -- fever, coughing and chest pains. After several days, the symptoms may progress to severe breathing problems and shock. Symptoms can develop two days to eight weeks after exposure.

About 20 percent of untreated cases involving cutaneous anthrax are fatal, and 25 percent to 60 percent of untreated cases of gastrointestinal anthrax are fatal. About 90 percent of untreated inhalation anthrax cases are fatal.

The information about anthrax was compiled from the following sources:
Anthrax as a Biological Weapon
Centers for Disease Control and Prevention
The Department of Defense
The Johns Hopkins University
The Washington Post

Smallpox is a deadly disease caused by a virus known as variola, a Latin word meaning "speckled." The virus, which can cause red lesions and pustules on the skin, is spread most often by an infected person releasing saliva droplets from their mouth into the air. Those droplets are then inhaled by a susceptible person in close contact with the ill person. Contamination is also possible through bed linens and clothing. People are most infectious from during the first week of the illness, but the disease can still be transmitted to others through scabs that have separated from the skin. It is not known to be spread by animals or insects.

Outbreaks involve either variola minor or the more deadly variola major. Those suffering from variola major become bedridden during the eruption of the rash and remain so throughout the illness. Spread of infection is limited to close contacts. Variola minor, however, can be so mild that patients can remain ambulatory during the infectious phase of their illness and thus spread the virus far more widely.

Smallpox likely was first used as a biological weapon during the French and Indian Wars. British soldiers distributed blankets that had been used by smallpox patients to initiate outbreaks among American Indians. Epidemics occurred, killing more than 50 percent of many affected tribes.

Smallpox was eradicated in 1977. In 1980, the World Health Assembly recommended that all countries cease vaccination and that all laboratories destroy their stocks of the virus or transfer them to one of two World Health Organization reference labs. All countries reported compliance.

The vaccine against smallpox is a live virus vaccine that contains a related virus called vaccinia virus that provides immunity against infection. The vaccine does not contain the smallpox virus. If the vaccine is given within four days after exposure to smallpox, it can lessen the severity of the illness or even prevent it.

Routine vaccination against smallpox ended in 1972. The level of immunity, if any, among those who were vaccinated before 1972 is uncertain. Prior infection with the disease provides lifelong immunity.

Patients with smallpox could benefit from supportive therapy, such as intravenous fluids and medicine to control fever or pain, and antibiotics for secondary bacterial infections.

The incubation period is seven to 17 days following exposure. Symptoms include high fever, fatigue, headaches and backaches, which are followed by a rash with lesions that develops within two to three days on mostly the face, arms and legs. Those lesions are round, tense and deeply embedded in the skin. They fill with pus and begin to crust early in the second week of the rash. Scabs eventually develop and fall off after three to four weeks. Lesions in the mouth and throat that appear early in the illness ulcerate and release large amounts of the virus in saliva. Severe abdominal pain and delirium are other symptoms that are sometimes present.

The majority of patients with smallpox recover, but death occurs in up to 30 percent of the cases. Most of those deaths occurred during the first or second week of illness. Sixty-five percent to 80 percent of survivors are marked with deep-pitted scars. Blindness is another possible complication for survivors of smallpox.

The information about smallpox was compiled from the following sources:
CDC Smallpox FAQ
CDC Facts about Smallpox

The Washington Post

Botulism is a muscle-paralyzing disease caused by a nerve toxin produced by a bacterium called Clostridium botulinum. Botulinum toxin in solution is colorless, odorless and, as far as is known, tasteless. Spores of Clostridium botulinum are found in the soil worldwide. The bacteria poses a major bioweapons threat because of its extreme potency and lethality; its ease of production, transport and misuse; and the potential need for prolonged intensive care in affected persons. Botulinum toxin is the single most poisonous substance known. There are three main types of botulism: infant, food-borne and wound.

Infant botulism occurs when living bacteria or the spores are ingested by an infant, and become planted in the infant's gastrointestinal tract. Honey and corn syrup, food products tolerated well by adults, have been associated with the disease in infants.

Food-borne botulism usually occurs when a person consumes food that has been improperly preserved or canned. Outbreaks from commercial products and foods prepared in restaurants have also occurred.

Wound botulism is caused by the growth of living botulism bacteria in a wound, with ongoing secretion of toxin that causes the paralytic illness. In the United States, this syndrome is seen almost exclusively in injecting drug users.

Although no instances of waterborne botulism have ever been reported, the potency of the toxin has led to speculation that it might be used to contaminate a municipal water supply. However, botulinum toxin is rapidly inactivated by standard water treatments such as chlorination and aeration. In addition, the slow turnover time of large-capacity reservoirs would require a comparably large amount of the toxin, which would be technically difficult to produce and deliver. Botulinum toxin cannot be spread from person to person.

To prevent infant botulism, it is recommended that honey and corn syrup not be fed to infants less than 1 year old. Because high temperatures destroy the botulism toxin, persons who eat home-canned foods should consider boiling the food for 10 minutes before eating it to ensure safety. Any food that has a foul odor should not be opened or consumed.

A person suffering from respiratory failure or paralysis may require being on a ventilator for weeks, plus intensive medical and nursing care. The paralysis slowly improves, usually over several weeks. If diagnosed early, food-borne and wound botulism can be treated with an antitoxin from horse serum that blocks the action of toxin circulating in the blood. That can prevent the patient from worsening, but recovery may still take many weeks.

Symptoms of exposure to the toxin may include blurred or double vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth and muscle weakness which always descends the body: first shoulders, then upper arms, lower arms, thighs, calves, etc. For food-borne botulism, symptoms begin from six hours to two weeks after eating toxin-containing food. Most commonly the delay is about 12 to 36 hours. Infants with botulism appear lethargic, feed poorly, are constipated and have a weak cry and muscle tone.

With prompt medical treatment, the risk of death can be significantly reduced. Most paralysis slowly goes away with time and treatment. The length and intensity of treatment varies for each individual based on the amount of toxin one has been infected with. In some cases, a victim may have to go through several months of therapy and remain on respirators.

The information about botulism was compiled from the following sources:
Botulinum Toxin as a Biological Weapon
National Institutes of Health
Michigan Department of Community Health:,1607,7-132-2945-12994--,00.html#Botulism
Virginia Department of Health:
Johns Hopkins:
Additional Related Links:
Bioterrorism Photo Gallery

Plague is an infectious disease of animals and humans caused by a bacterium named Yersinia pestis. People usually get plague from being bitten by a rodent flea that is carrying the plague bacterium or by handling an infected animal. Millions of people in Europe died from plague in the Middle Ages, when human homes and places of work were inhabited by flea-infested rats.

There are three types of the plague: bubonic, pneumonic, and septicemic. Bubonic plague is the most common form of plague. It occurs when an infected flea bites a person or when materials contaminated with the bacteria enter through a break in a person's skin. This form of plague does not spread from person to person. Septicemic plague occurs when the bacteria multiply in the blood. It can be a complication of the pneumonic or bubonic plague or can occur by itself. When it occurs alone, it is caused in the same way as bubonic plague. Pneumonic plague occurs when the bacteria infect the lungs. Transmission can take place if someone breathes in aerosolized bacteria or by breathing in the respiratory droplets of a person or animal with the disease. It may occur if bubonic or septicemic plague is untreated and the bacteria spread to the lungs.

Plague's history as a biological weapon dates to World War II, when a secret branch of the Japanese army was reported to have dropped plague-infected fleas over China causing outbreaks. Both the United States and the Soviet Union then developed techniques to aerosolize plague. The U.S. program was terminated in 1970.

Attempts to eliminate fleas and wild rodents from the natural environment in plague-infected areas are impractical. However, controlling rodents and their fleas around places where people live, work, and play is very important in preventing human disease. Eliminate sources of food and nesting places for rodents; remove brush, rock piles, junk, cluttered firewood, and potential food supplies, such as pet and wild animal food. If you anticipate being exposed to rodent fleas, apply insect repellents to clothing and skin to prevent flea bites.

Health authorities advise that antibiotics be given for a brief period to people exposed to someone with pneumonic plague. They also suggest treating people who have been exposed to the bites of potentially infected rodent fleas (for example, during a plague outbreak) or who have handled an animal known to be infected with the plague bacteria. People who must be present in an area where a plague outbreak is occurring can protect themselves for two to three weeks by taking antibiotics, such as the tetracyclines or the sulfonamides. Plague vaccine has very limited use and is administered to scientists who routinely work with the plague bacteria and people in plague-infested areas who handle or have close contact with potentially infected animals as part of their routine work (such as rodent biologists).

The sign that plague is present is a very painful, usually swollen and often hot-to-the touch lymph node, called a bubo. Onset of bubonic plague is usually two to six days after a person is exposed. Symptoms of bubonic plague are muscular pain, high fever, chills, headaches, swelling of lymph glands (called buboes) in the armpits, neck, groin and other areas. In some cases, seizures can occur. Symptoms for septicemic plague can include nausea, vomiting, fever, low blood pressure, chills, abdominal pain, shock and bleeding into skin and other organs. The incubation period of primary pneumonic plague is one to three days and is characterized by development of an overwhelming pneumonia with high fever, cough, bloody sputum and chills.

If treated immediately, a full recovery is possible. The risks of death become higher the longer symptoms go untreated. For plague pneumonia patients, the death rate is more than 50 percent.

The information about Plague was compiled from the following sources:
Plague as a Biological Weapon
Johns Hopkins Center for Civilian Biodefense Strategies:
National Institutes of Health

American College of Physicians-American Society of Internal Medicine:

Tularemia is a bacterial disease that is associated by both animals and humans. Also known as "Rabbit Fever" and "Deer's Fly Fever," Tularemia in animals is caused by the bacteria Francisella tularensis. It is spread to humans via ticks and infected animal tissue and in some cases from contaminated food and water. Tularemia is not spread from person to person. The bacteria are highly infectious: a small number of bacteria (10-50 organisms) can cause the disease.

If F. tularensis were used as a bioweapon, the bacteria would likely be made airborne for exposure by inhalation. Persons who inhale an infectious aerosol would generally experience severe respiratory illness, including life-threatening pneumonia and systemic infection, if they were not treated. The bacteria that cause tularemia occur widely in nature and could be isolated and grown in quantity in a laboratory, although manufacturing an effective aerosol weapon would require considerable sophistication.

Tularemia is often treated with antibiotics. To prevent Tularemia, several precautions should be taken. Wear light-colored long-sleeved shirts and long pants when in wooded areas to avoid being bitten by ticks and be sure to keep the lawn around homes mowed and weeds cut. In the past, a vaccine for tularemia was available, but it is currently under review by the Food and Drug Administration.

The incubation period for tularemia is typically three to five days, with symptoms occurring from one to 14 days. Depending on the route of exposure, the tularemia bacteria may cause skin ulcers, swollen and painful lymph glands, inflamed eyes, sore throat, oral ulcers, or pneumonia. If the bacteria were inhaled, symptoms would include the abrupt onset of fever, chills, headache, muscle aches, joint pain, dry cough and progressive weakness. Persons with pneumonia can develop chest pain, difficulty breathing, bloody sputum, and respiratory failure.

If untreated, Tularemia is fatal in about 5 percent to 15 percent of all cases. Forty percent or more of the people with the lung and systemic forms of the disease may die if they are not treated with appropriate antibiotics.

The information about tularemia was compiled from the following sources:
Johns Hopkins Center for Civilian Biodefense Strategies:
Tularemia as a Biological Weapon
American College of Physicians-American Society of Internal Medicine:
MEDLINEplus Medical Encyclopedia:

Ricin is a naturally occurring substance that can be isolated and used as a toxin. It is found in the castor plant, which is grown agriculturally worldwide and grows in the wild in parts of the United States. Castor beans are used to make castor oil, a digestive agent as well as a component of brake and hydraulic fluids. When castor beans are made into castor oil, the ricin is discarded.

Ricin can be easily and inexpensively produced. It must be inhaled, ingested or injected to be an effective toxin.

Ricin gets inside cells and prevents them from making needed proteins, leading to organ and system failure.

A stable substance not affected by extremely hot or cold temperatures, ricin can be used to contaminate food or water supplies.

In the case of injection, ricin detection is difficult. In 1978, it was used to kill Bulgarian dissident Georgi Markov. A ricin-coated pellet was injected into his leg using a specially equipped umbrella. He died three days later.

Even a tiny amount of ricin is toxic. 70 micrograms - the amount of a grain of salt - is enough to kill an adult. It is said that just one castor bean can kill a child.

Even a tiny amount of ricin is toxic. 70 micrograms - the amount of a grain of salt - is enough to kill an adult. It is said that just one castor bean can kill a child.

Because no antidote exists for ricin, the most important factor is avoiding ricin exposure in the first place. If exposure cannot be avoided, the most important factor is then getting the ricin off or out of the body as quickly as possible. Ricin poisoning is treated by giving victims supportive medical care to minimize the effects of the poisoning.

Using a respiratory mask may help prevent inhalation of ricin. It is not contagious and cannot be spread from person to person.

Because no antidote exists for ricin, the most important factor is avoiding ricin exposure in the first place. If exposure cannot be avoided, the most important factor is then getting the ricin off or out of the body as quickly as possible. Ricin poisoning is treated by giving victims supportive medical care to minimize the effects of the poisoning.

Symptoms may appear in less than an hour or may not appear for several days after exposure.

Inhaled or injected ricin may cause respiratory problems, chest pain weakness, fever, cough, cyanosis (blue skin) and pulmonary edema within 24 hours of exposure. Severe respiratory distress and death may occur in 36 to 72 hours.

Ingested ricin may cause diarrhea, nausea, vomiting, abdominal cramps, internal bleeding, liver and kidney failure, and gastroenteritis. The heart rate may be rapid.

Injected ricin may cause tissue damage near the injection site as well as multiple organ failure.

Ricin also can affect the central nervous system, causing seizures.

All methods of exposure are dangerous and may be fatal. After five days without complications, an exposed person will probably not die.