This is the first in a series of articles exploring BW and vaccines, using anthrax as the example. This first article presents a summary of what is known about the pathogenicity of anthrax, as a prelude of how a vaccine can work to prevent the disease. The second article will explore the history of development of anthrax vaccines. The third article will discuss some of the complications of the anthrax vaccines and their possible role in the Gulf War Syndrome.

Biological Warfare and Vaccines: Anthrax

Meryl Nass and Barbara Price


Part 1. Pathogenicity and Virulence of Anthrax

The information on the pathogenicity was taken from numerous reference materials, various Internet sources, and Medical Aspects of Chemical and Biological Warfare, Office of the Surgeon General, Department of the Army, USA (1997).

The Infecting Organism

Anthrax is a disease primarily of mammals and birds caused by the anthrax bacterium (Bacillus anthracis). The B. Anthracis, is a large, Gram-positive, spore-forming, nonmotile, rod-shaped bacillus (1-1.5 Ám by 5 -10 Ám), which grows on ordinary nutrient media and in soil, aerobically and anaerobically. Its genotype and phenotype are similar to Bacillus cereus, a bacteria readily isolated from soil cultures.

Exposure and Clinical Symptoms

Humans become infected with anthrax:
  • cutaneously, through cuts or abrasions on skin when handling infected animals, carcasses, meat, or contaminated soil,
  • through digestion of infected meat, (oropharyngeal and gastrointestinal anthrax) or
  • by inhalation of anthrax spores, usually on dust from animal hair or hides ("Woolsorter's disease").

Cutaneous anthrax is characterized by a small papule that forms at the site of the infection associated a gelatinous edema caused by the germination of the spores. The papule develops into a vesicle and finally into a necrotic ulcer. There is often an edema around the ulcer, which can encompass the affected limb. If untreated, septicemia may develop, but with treatment mortality is less than 1%. 

Anthrax caused by ingestion is very rare in humans. Oropharyngeal anthrax develops with a sore throat, fever and swelling of the neck due to swollen lymph nodes and edema. Gastrointestinal anthrax progresses via nausea and vomiting followed by abdominal pain and bloating from accumulation of fluid in the peritoneum. The mortality for digestive forms of anthrax is estimated as 50% or higher.

Inhalation anthrax may begin 1 - 6 days after exposure with a general malaise and chest pain. There is increasing respiratory distress and high fever and may be edema of the neck or chest, excessive sweating, and cyanosis. Inhalation anthrax is almost invariably fatal.

Weaponized anthrax would most likely be inhalation anthrax.

Virulence

Until the 1950s, it was thought that anthrax fatalities resulted from capillaries blocked by large numbers of B.anthracis bacteria. However, anthrax bacilli release an exotoxin that diffuses into the blood and causes symptoms of anthrax when injected into test animals. Since then, three different antigenic components, proteins with molecular weights about 80kDa have been found to make anthrax toxin. Although the exact pathogenic mechanism of the disease is not known, the virulence of anthrax appears to be a result of the toxins and the protective capsule around the organism.

Anthrax is one of the bacteria that forms a capsule around the organism to protect it from being ingested by phagocytes. The anthrax bacterium's cell wall is made of an antigenic polysaccharide. The capsule is made of poly D-glutamate polypeptide and is also antigenic. All virulent anthrax forms this capsule. This capsule is important in establishing the infection. In addition to the antigenic capsule anthrax has three antigenic components of an exotoxin, anthrax toxin.

The protective antigen (PA) is an immunogenic protein. The PA is a B protein (a cell-binding protein) and works with each of the two other virulence factors, which are A proteins, to elicit toxic responses. Lethal Factor (LF) is a protein that combines with PA to form a toxin that is essential for the lethal effects of anthrax (lethal toxin). Edema Factor (EF) is an inherent adenylate cyclase, similar to Bordetella pertussis's (whooping cough) adenylate cyclase toxin. EF, in combination with PA, forms the edema toxin responsible for producing the edema in anthrax. Neither LF nor EF are inherently toxic; only in combination with PA. EF+PA produces edema toxin; LF+PA produces lethal toxin; EF+LF appears to be inactive; and EF+LF+PA produces edema and necrosis and is lethal. All three genes for PA, LF and EF are on one plasmid, pX01, separate from the plasmid that has the genes for the capsule, pX02.

The exact pathogenic mechanisms for EF, LF and PA in the disease are still being researched. On April 30, 1998, in Science (Duesbury, N. S., Science 280, p.734, "Proteolytic Inactivation of MAP-Kinase-Kinase by Anthrax Lethal Factor"), the results of recent studies on LF were presented. LF has been shown to prevent frog oocytes from maturing into eggs, indicating possible blockage of the MAPK pathway, a major pathway for regulating cell proliferation and growth. The LF protein clips off a piece of the enzyme responsible for activating MAPK. By identifying a target molecule for LF, researchers can then look for drugs that interfere with LF's enzymatic activity. This approach is different from the approach used for vaccines.

Vaccines

From Current Med Talk: Vaccines are a mixture of live, live-attenuated (decreased virulence), killed, complete or incomplete microorganisms or products derived therefrom that contains antigens capable of stimulating the production of specific protective antibodies against a microorganism. Modern understanding goes even further with some authors acknowledging the role immunology plays by requiring a vaccine to contain a sufficient number of different T-cell epitopes (sites, "hills and ridges," that elicit an antigenic response) so that T-cell responses are achieved in all members of a genetically diverse outbred population. A vaccine should generate a large pool of memory T- and B-cells, so that the greater the size of the pool, the more rapid the appearance of effector T-cell activity from the memory cells. The titer of antibodies should be high enough so that most of a challenge organism is prevented from infecting susceptible cells. Newer recombinant and DNA vaccines may also include other properties.

Adjuvants are substances administered with an antigen to elicit an immune response to the antigen. Adjuvants are sometimes used in vaccines to stimulate the immunsystem and make the vaccine more effective. Adjuvants can be derived from materials as diverse as silica gel, synthetic polymers and dead mycobacteria. Adjuvants must be selected carefully because some may induce diseases.

Part 2. History of Anthrax Vaccine Development

Part 3. Side Effects of Anthrax Vaccine and Possible Connections with Gulf War Syndrome

References:

  1. Medical Aspects of Chemical and Biological Warfare, Office of the Surgeon General, Department of the Army, USA (1997).
  2. Current Med Talk: A Dictionary of Medical Terms, Slang and Jargon, J.C. Segen, Appleton & Lange, Stamford, CT (1995).
  3. Molecular Biology and Biotechnology: A Comprehensive Desk Reference, Ed. R.A. Meyers, VCH Publishers (1995).
  4. Prof. Jiri Bajgar, the Bard of ASA, gives to us his paraphrase (or perhaps soliloquy) on Shakespeare and the never ending quest of trying to find and promulgate the perfect word(s) and wording which in themselves might signify BTWC-VP progress.

98-4, issue no. 67


For the Professional in Government and Industry with an interest in Nuclear, Biological and Chemical Defense, Disarmament and Verification; Emergency and Disaster Medical Planning; Industrial Health and Safety; and Environmental Protection

 

 

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