Toxins
█ BRIAN HOYLE
Toxins are compounds that are produced and released by a variety of microorganisms and other organisms. Toxins can be fast-acting and, because they are already preformed, do not require the growth of a microorganism in the host. State-sanctioned weaponization programs for various toxins have occurred in the past in many countries, and may be ongoing. As well, toxins are a potent weapon for terrorists.
Bacterial toxins. Toxins are the main disease-causing factor for a number of bacteria. Some examples include Corynebacterium diphtheriae (diptheria), Vibrio cholerae (cholera), Bacillus anthracis (anthrax), Clostridium botulinum (botulism), certain strains of Escherichia coli (hemolytic uremic syndrome), and Staphylococcus aureus (toxic shock syndrome).
Certain species of these bacteria are of particular concern in biological warfare and biological terrorism. As the events of 2001 in the United States demonstrated, powdered preparations of Bacillus anthracis spores was easily delivered to a target through the mail. The dispersal of the spores in the air and the inhalation of the spores can cause a form of anthrax that develops quickly and, without treatment, is almost always fatal. The bacteria in the genus Clostridium also form spores. Additionally, during the 1990s, a strain of Staphylococcus aureus emerged that is resistant to almost all known antibiotics.
Bacterial toxins have a wide variety of activity. Some toxins damage the cell wall of host cells, either by dissolving the wall or by chemically punching holes through the wall. Examples of such toxins are the alpha toxin of Clostridium perfringens , hemolysin of Escherichia coli , and streptokinase of Streptococcus pyogenes . The damage to the host cells allows the bacteria to spread rapidly through the host. This can cause an overwhelming infection.
Other bacterial toxins kill host cells by stopping the manufacture of protein in host cells or by degrading the proteins. Examples of protein blockers include exotoxin A of Pseudomonas aeruginosa and the Shiga toxins produced by both Escherichia coli and Shigella dysenteriae . Protein degrading toxins include those produced by Bacillus anthracis and Clostridium botulinum
Still other toxins stimulate an immune response of the host that is so strong that it can damage the host. Staphylococcus aureus produces at least three different toxins that have this effect (i.e., toxic shock syndrome).
Marine toxins. Microorganisms called dinoflagellates can produce toxins when they grow in species of shellfish. Usually, the toxins are a concern when the contaminated seafood is inadvertently eaten. But, the toxins can be isolated in pure form. The purified toxins will produce illness when deliberately used.
Aflatoxin. Aflatoxin is produced by two species of mold— Aspergillus flavus and Aspergillus parasiticus . The toxin is especially a concern when potatoes are contaminated by the mold. Ingestion of the contaminated potatoes can cause serious, even fatal illness. This toxin is of particular concern for food supplies. Storehouses of produce like potatoes are susceptible to the malicious release of the molds.
Ricin. Ricin is a toxin that is produced by the castor bean. It is the third most deadly toxin that is known, after the toxins produced by Clostridium botulinum and Clostridium tetani . The symptoms of ricin toxin include nausea, muscle spasms, severe lung damage, and convulsions. These symptoms appear within hours, and, without treatment, death from pulmonary failure can result within three days. There is no vaccine or antidote for the toxin.
Ricin has long been a weapon of espionage and terrorism. The most famous use of ricin occurred in 1978, when Georgi Markov—a recently defected Bulgarian official—was killed by KGB agents on a bridge in London. An umbrella tip was used to inject a capsule of ricin into one of his legs.
The planned use of ricin by al-Qaeda has been alleged. Traces of ricin have been found in caves in Afghanistan that were used by al-Qaeda. Iraq is also suspected of using ricin in its weaponization program of the 1990s. Also, in January 2003, British antiterrorism officers seized a quantity of ricin in London from a group of Algerian men suspected of being terrorists.
Toxoid vaccines. Some toxins that are capable of causing much harm are also a source of protection. Because of its potency, a toxin cannot be used protectively in its unaltered form. Toxins can be altered, however, so that they do not produce the undesirable effects, but which still stimulate the immune system to produce antibodies to a critical part of the toxin molecule. The weakened version of a toxin is called a toxoid.
The anthrax vaccine that is currently licensed for use contains two toxoids in addition to other immune stimulating molecules. The immune response will produce antibodies to the two toxins of the anthrax bacterium.
█ FURTHER READING:
PERIODICALS:
Schmitt, C. K., K. C. Meysick, and A. D. O'Brien. "Bacterial Toxins: Friends or Foes?" Emerging Infectious Diseases no. 5 (1999): 224–34.
ELECTRONIC:
Centers for Disease Control and Prevention. "Marine Toxins." Division of Bacterial and Mycotic Diseases. June 10, 2002. < http://www.cdc.gov/ncidod/dbmd/diseaseinfo/marinetoxins_g.htm >(29 January 2003).
United States Department of Agriculture. "Aflatoxin." USDA Grain Inspection, Packers and Stockyards Administration. September 17, 1998. < http://www.usda.gov/gipsa/newsroom/backgrounders/b-aflatox.htm >(29 January 2003).
University of Wisconsin at Madison. "Mechanisms of Bacterial Pathogenicity: Protein Toxins." Bacteriology at UW-Madison. 2002. < http://www.bact.wisc.edu/Bact330/lecturept >(30 January 2003).
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