Biological Agents: Anthrax, Plague, Smallpox, and Ricin

According the Chemical and Biological Arms Control Institute, "The vulnerabilities of the United States to a bioterrorism attack are virtually infinite." Damaging biological agents (disease-causing organisms) can be spread unknowingly, possibly causing more devastation than a nuclear weapon. Terrorists may choose to use a biological agent for a variety of reasons: the self-replicating capacity of some biological agents, the relative low cost of producing biological weapons, and the insidious symptoms that can mimic other diseases. A bioterrorist attack could be waged through a variety of agents, including bacteria (anthrax, plague, tularemia, brucellosis), viruses (smallpox, hemorrhagic fever, viral encephalitides), and toxins (ricin, botulinum, saxitoxin). Below are summaries of some of these bioterrorist agents and resources for additional information regarding them.

Anthrax is an infectious disease caused by the spore-forming bacterium Bacillus anthracis. Human anthrax has three major clinical forms: cutaneous, inhalation, and gastrointestinal. Cutaneous anthrax results from the introduction of a spore through a break in the skin, which causes a localized infection. Inhalation and gastrointestinal anthrax result from the introduction of a spore through the respiratory tract and oral ingestion, respectively. The release of anthrax by a terrorist group will most likely involve an aerosol form, due to the stability of the spore and ease of travel. Symptoms of the disease vary depending on how the spore was introduced into the body, but they usually occur within 7 days following exposure. Symptoms of inhalation anthrax first mirror influenza but are rapidly followed by severe respiratory distress, which leads to shock and death within 36 hours after the onset of symptoms. Vaccination and antibiotic treatment are available for those at risk of exposure to anthrax.

Plague is an infectious disease of animals and humans caused by a bacterium named Yersinia pestis that is typically transmitted through rodent flea bites and the handling of infected animals. There are three types of plague: pneumonic, bubonic, and septicemic. Pneumonic plague occurs when the bacterium infects the lungs, causing high fever, chills, headache, respiratory failure, and circulatory collapse. Pneumonic plague can spread from human contact through the air. Because of its devastating effects and ease of distribution, pneumonic plague is the most likely type of plague to be used by a terrorist group. Bubonic plague occurs when an infected flea bites a person or when materials contaminated with Yesrinia pestis enter the body through a break in the skin. Symptoms include malaise, fever, and tender lymph nodes, but bubonic plague can also affect the central nervous system and lungs. Septicemic plague occurs when plague bacteria multiply in the blood; it can develop in individuals who have already developed pneumonic or bubonic plague.

Smallpox is a contagious disease with a fatality rate of 30 percent. Smallpox has two clinical forms: variola major and variola minor. Variola major is the severe and most common form of smallpox; it causes an extensive rash and high fever. There are four types of variola major smallpox: ordinary, modified (mild and occurring in previously vaccinated persons), flat, and hemorrhagic, the last two of which are rare and extremely severe. Variola minor is a less severe variation of the disease. Transmission of the disease occurs through direct and prolonged human contact and through an aerosol. Smallpox can also be spread through direct contact with infected body fluids or contaminated objects such as bedding or clothing. Once a person is exposed to the virus, the incubation period lasts between 7 to 17 days.

Ricin toxin, found in the bean of the castor plant, Ricinis communis, is one of the most toxic and easily produced plant toxins. Ricinis communis was originally cultivated in ancient Egypt as a lubricant and laxative. Today, castor beans are used in the production of castor oil, a brake and hydraulic fluid constituent that can be found throughout the world. Waste from the commercial production of castor oil contains 50 percent ricin. Because of its relatively high toxicity and its ease of production, ricin was studied and developed as a biological weapon by the United States during World War I and World War II. More recently, the toxin has found its way into the arsenals of extremist individuals, groups, and governments. Toxic reactions to ricin occur from three exposure routes: inhalation, oral ingestion, and injection. Although oral ingestion is the least toxic, inhalation of ricin would likely produce symptoms, including fever, cough, nausea, and respiratory failure, within 8 hours. Depending on the dose, death will occur within 36–72 hours after exposure. Unfortunately, no specific vaccines are available to counter ricin poisoning.

Emerging Infectious Diseases (PDF)
National Center for Infectious Diseases, July–August 1999

Textbook of Military Medicine: Medical Aspects of Chemical and Biological Warfare Office of the Surgeon General, Department of the Army, 1997

Ricin Toxin (PDF) (Chapter 32 in the Textbook of Military Medicine)
United States Army Medical Research Institute of Chemical Defense, 1997

Helpful Resources

Public Health Emergency Preparedness & Response/Centers for Disease Control and Prevention

Anthrax Vaccine Immunization Program

Chemical and Biological Arms Control Institute

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