Reasonable Rascal
07-10-01, 23:37
Anthrax
Author:
Timothy Paustian
Tuesday, July 25, 2000
Who would have imagined that the first bacterium found to be the cause of a disease over one hundred years ago would still be a hot topic in the newspaper headlines today. Anthrax is a highly lethal disease caused by Bacillus anthracis. In 1877, Robert Koch grew the organism in pure culture, demonstrated its ability to form endospores, and produced experimental anthrax by injecting it into animals (2). Bacillus anthracis is a large, Gram-positive, motile, spore forming bacterial rod. The microbe can be cultivated in minimal nutrient media in aerobic or nonaerobic conditions (2). The bacilli have a wide range of physiologic abilities that allow them to live in every natural environment, including the ability to form endospores. Each anthracis cell produces one endospore, which is resistant to heat, cold, radiation, desiccation, and disinfectants. In order for the endospore to return to a living, growing cell, oxygen must be present. This need for oxygen is an important constraint for controlling the anthrax disease (5).
So, what is it that makes this bacterium so lethal and dangerous? Three bacterial components of Bacillus anthracis attribute to its virulence. First, Bacillus anthracis has a unique cell wall polysaccharide antigen.
This forms a single antigenic type of capsule consisting of poly-D-glutamate peptide (2). The capsule itself is non-toxic and functions as protection against phagocytic engulfment. The role of the capsule is most important during the establishment of the infection. However, during the terminal phases of the disease, it is the role of the anthrax toxin that is most significant. Three proteins produced by Bacillus anthracis, the
protective antigen (PA), the lethal factor (LF), and the edema factor (EF) combine in pairs to form the lethal (PA+LF) and edema (PA+EF) toxins (1). The edema factor is necessary for the edema producing activity of the toxin and the protective antigen is the binding domain of the anthrax toxin. Lastly, the lethal factor is essential for the lethal effects of anthrax.
Both the capsule and the three toxins are important due to their direct effects on phagocytes. Although
phagocytes migrate to the site of the lesion with anthrax bacilli, the encapsulated organism is able to resist
their engulfment. Once the toxins enter circulation, the disease becomes systemic and death often occurs.
The infectious bacterial disease, Anthrax, is spread by contact with infected animals, handling infected
products, eating infected meat, or breathing weapon dispersed anthrax spores. Although the number of modes of infection is high, anthrax in humans is very rare. There are three forms of the anthrax disease: Cutaneous, gastrointestinal and inhalation. Cutaneous anthrax, the most common form of the disease in humans, is often caused by contact with infected animals or contaminated animal products. Usually an exposed area of skin or mucous membrane is inoculated by spores from the soil or a contaminated animal (2). Edema develops at the site and eventually a pustule is formed leading to a necrotic ulcer. Septicemia can develop and if the blood stream is invaded, the disease can be fatal. Gastrointestinal anthrax is usually caused by ingestion of contaminated meat. Food poisoning often occurs because spores survive cooking or pasteurization and then germinate and multiply when the food is inadequately refrigerated (5). Symptoms of diarrhea and abdominal pain, or nausea and vomiting occur within 5-10 hours after the food is eaten.
Inhalation anthrax is yet another form of the disease, resulting from inhalation of anthrax spores. This form is most deadly because the airborne anthrax spores are inhaled and lodged in the lungs, where they then migrate to the lymph nodes, change to the bacterial form, multiply and produce toxins (6). The toxins are then spread through the body via the bloodstream often leading to shock and death within 24-48 hours. Death is due to oxygen depletion, secondary shock, increased vascular permeability and respiratory failure. The symptoms of the disease begin with flu-like aches and pains, gradually developing into fever, fatigue, malaise, coughing and chest discomfort. Eventually the individual will experience severe difficulty in breathing. Inhalation anthrax is diagnosed by isolating the bacteria from the blood or skin lesions, or by a blood culture, which measures the specific antibodies produced late in the course of the disease. Antibiotics can be used to treat anthrax exposure- - if administered within 12 hours, however, symptoms often do not occur until after this deadline has passed and it is then too late for treatment (3).
The only way to essentially control the anthrax disease is to prevent it from occurring at all. The anthrax
vaccine for humans was developed in the U.S. during the 1950s and 1960s, and approved by the FDA in 1970 (6). The vaccine is a cell-free filtrate, produced by a strain of anthrax that does not cause disease. It contains no whole bacteria, dead or alive. Basically, the vaccine is the solution that results after filtration of a culture of anthrax bacteria. Vaccination is the only way to aid the immune system in preventing Bacillus anthracis from growing and producing the toxins that lead to disease and death. There have been no patterns of long-term or delayed side effects from the vaccine. Although 50% of women reported mild local reactions, such as aching at the site of injection, only 1-2% of the vaccinated population have shown large local effects, while less than 0.2% have experienced systemic reactions (6). The human anthrax vaccine consists of a series of 6 doses with yearly boosters, and the first vaccine of the series must be given 4 weeks before exposure to the disease. Due to the lethality of anthrax, the vaccine is available for people in high-risk occupations. By the year 2005 the entire military force between the ages of 18 and 65 will also begin receiving the six shot series to protect them against the possibility of anthrax spores being used against them.
Iraq, Russia, and as many as ten nations have the capability to load spores of Bacillus anthracis into
weapons. These spores can be stored in a dry form and remain viable for decades in storage or after release
(2). When released, the spores are easily dispersed in air for unprotected troops and civilians to inhale, and
may remain in the soil for several years. Despite the danger military troops could face, several service
members are reluctant to be vaccinated due to their concern of adverse effects. Unexpectedly, the mandatory vaccination program has posed a substantial challenge to the department of defense and remains very controversial. Therefore, although anthrax is quite rare in human beings, if anthrax spores were to be used for biological weapons, millions of people could be in danger. Few humans in the U.S. have experienced the devastating effects of anthrax, however, due to its lethality and possible use as a weapon, everyone should be educated about it.
References
1.Brossier, F, Mock, M, Sirard, J, Weber-Levy, M. 2000. Role of toxin domains in anthrax pathogenesis.
Infection and Immunity. 68: 1781-1786.
2.http://www.bact.wisc.edu/Bact330/lectureanthrax
3.http://www.cnn.com/HEALTH/9802/19/anthrax.explainer/
4.http://www.cdc.gov/ncidod/dbmd/diseaseinfo/anthrax_g.htm
5.http://129.109.112.248/microbook/ch015.htm
6.http://www.anthrax.osd.mil/
Author:
Timothy Paustian
Tuesday, July 25, 2000
Who would have imagined that the first bacterium found to be the cause of a disease over one hundred years ago would still be a hot topic in the newspaper headlines today. Anthrax is a highly lethal disease caused by Bacillus anthracis. In 1877, Robert Koch grew the organism in pure culture, demonstrated its ability to form endospores, and produced experimental anthrax by injecting it into animals (2). Bacillus anthracis is a large, Gram-positive, motile, spore forming bacterial rod. The microbe can be cultivated in minimal nutrient media in aerobic or nonaerobic conditions (2). The bacilli have a wide range of physiologic abilities that allow them to live in every natural environment, including the ability to form endospores. Each anthracis cell produces one endospore, which is resistant to heat, cold, radiation, desiccation, and disinfectants. In order for the endospore to return to a living, growing cell, oxygen must be present. This need for oxygen is an important constraint for controlling the anthrax disease (5).
So, what is it that makes this bacterium so lethal and dangerous? Three bacterial components of Bacillus anthracis attribute to its virulence. First, Bacillus anthracis has a unique cell wall polysaccharide antigen.
This forms a single antigenic type of capsule consisting of poly-D-glutamate peptide (2). The capsule itself is non-toxic and functions as protection against phagocytic engulfment. The role of the capsule is most important during the establishment of the infection. However, during the terminal phases of the disease, it is the role of the anthrax toxin that is most significant. Three proteins produced by Bacillus anthracis, the
protective antigen (PA), the lethal factor (LF), and the edema factor (EF) combine in pairs to form the lethal (PA+LF) and edema (PA+EF) toxins (1). The edema factor is necessary for the edema producing activity of the toxin and the protective antigen is the binding domain of the anthrax toxin. Lastly, the lethal factor is essential for the lethal effects of anthrax.
Both the capsule and the three toxins are important due to their direct effects on phagocytes. Although
phagocytes migrate to the site of the lesion with anthrax bacilli, the encapsulated organism is able to resist
their engulfment. Once the toxins enter circulation, the disease becomes systemic and death often occurs.
The infectious bacterial disease, Anthrax, is spread by contact with infected animals, handling infected
products, eating infected meat, or breathing weapon dispersed anthrax spores. Although the number of modes of infection is high, anthrax in humans is very rare. There are three forms of the anthrax disease: Cutaneous, gastrointestinal and inhalation. Cutaneous anthrax, the most common form of the disease in humans, is often caused by contact with infected animals or contaminated animal products. Usually an exposed area of skin or mucous membrane is inoculated by spores from the soil or a contaminated animal (2). Edema develops at the site and eventually a pustule is formed leading to a necrotic ulcer. Septicemia can develop and if the blood stream is invaded, the disease can be fatal. Gastrointestinal anthrax is usually caused by ingestion of contaminated meat. Food poisoning often occurs because spores survive cooking or pasteurization and then germinate and multiply when the food is inadequately refrigerated (5). Symptoms of diarrhea and abdominal pain, or nausea and vomiting occur within 5-10 hours after the food is eaten.
Inhalation anthrax is yet another form of the disease, resulting from inhalation of anthrax spores. This form is most deadly because the airborne anthrax spores are inhaled and lodged in the lungs, where they then migrate to the lymph nodes, change to the bacterial form, multiply and produce toxins (6). The toxins are then spread through the body via the bloodstream often leading to shock and death within 24-48 hours. Death is due to oxygen depletion, secondary shock, increased vascular permeability and respiratory failure. The symptoms of the disease begin with flu-like aches and pains, gradually developing into fever, fatigue, malaise, coughing and chest discomfort. Eventually the individual will experience severe difficulty in breathing. Inhalation anthrax is diagnosed by isolating the bacteria from the blood or skin lesions, or by a blood culture, which measures the specific antibodies produced late in the course of the disease. Antibiotics can be used to treat anthrax exposure- - if administered within 12 hours, however, symptoms often do not occur until after this deadline has passed and it is then too late for treatment (3).
The only way to essentially control the anthrax disease is to prevent it from occurring at all. The anthrax
vaccine for humans was developed in the U.S. during the 1950s and 1960s, and approved by the FDA in 1970 (6). The vaccine is a cell-free filtrate, produced by a strain of anthrax that does not cause disease. It contains no whole bacteria, dead or alive. Basically, the vaccine is the solution that results after filtration of a culture of anthrax bacteria. Vaccination is the only way to aid the immune system in preventing Bacillus anthracis from growing and producing the toxins that lead to disease and death. There have been no patterns of long-term or delayed side effects from the vaccine. Although 50% of women reported mild local reactions, such as aching at the site of injection, only 1-2% of the vaccinated population have shown large local effects, while less than 0.2% have experienced systemic reactions (6). The human anthrax vaccine consists of a series of 6 doses with yearly boosters, and the first vaccine of the series must be given 4 weeks before exposure to the disease. Due to the lethality of anthrax, the vaccine is available for people in high-risk occupations. By the year 2005 the entire military force between the ages of 18 and 65 will also begin receiving the six shot series to protect them against the possibility of anthrax spores being used against them.
Iraq, Russia, and as many as ten nations have the capability to load spores of Bacillus anthracis into
weapons. These spores can be stored in a dry form and remain viable for decades in storage or after release
(2). When released, the spores are easily dispersed in air for unprotected troops and civilians to inhale, and
may remain in the soil for several years. Despite the danger military troops could face, several service
members are reluctant to be vaccinated due to their concern of adverse effects. Unexpectedly, the mandatory vaccination program has posed a substantial challenge to the department of defense and remains very controversial. Therefore, although anthrax is quite rare in human beings, if anthrax spores were to be used for biological weapons, millions of people could be in danger. Few humans in the U.S. have experienced the devastating effects of anthrax, however, due to its lethality and possible use as a weapon, everyone should be educated about it.
References
1.Brossier, F, Mock, M, Sirard, J, Weber-Levy, M. 2000. Role of toxin domains in anthrax pathogenesis.
Infection and Immunity. 68: 1781-1786.
2.http://www.bact.wisc.edu/Bact330/lectureanthrax
3.http://www.cnn.com/HEALTH/9802/19/anthrax.explainer/
4.http://www.cdc.gov/ncidod/dbmd/diseaseinfo/anthrax_g.htm
5.http://129.109.112.248/microbook/ch015.htm
6.http://www.anthrax.osd.mil/