Germs Book: Don't Touch That Doorknob!
B. anthracis has been a scourge of humankind for centuries. In fact, it is this organism and the disease it causes, anthrax, that was the basis of what are known as Koch's postulates. Koch's potulates are a series of inter-relationships that can be used to establish that a suspected microorganism is in fact the cause of a particular infectious disease.
B. anthracis is an aerobic organism, meaning that the bug requires molecular oxygen (O2) to flourish. However, this bacterium can also exist quite well when the available oxygen is very low. Interestingly, in the presence of high oxygen concentrations, such as one finds in air, the organism immediately changes to what is known as an endospore. Endospore formation is common to the genus Bacillus, and is a special form of the bacterial cell that is highly resistant to heat, dessication (lack of water) and radiation. This endospore form of the organism essentially exists in a state of "suspended animation." Once the organism infects an animal or human, however, the endospore reverts to what is named a vegetative cell. It is the vegetative cell that causes the disease. This conversion occurs because (1) oxygen levels are lower and (2) necessary nutrients become available upon infection of a host. These nutritional requirements are relatively high compared to other microorganisms, consequently, Bacillus anthracis cannot exist as a viable, vegetative cell in the absence of such nutrients or in the presence of high oxygen levels - thus - the conversion to an endospore when absent from a host (hooved animal or human).
The disease, anthrax, is most commonly found in domesticated, hooved animals. And, in the U.S. as well as other countries, there is an on-going effort to prevent animals such as cattle, for example, from contracting the disease. Animals are routinely vaccinated with a preparation of the organism that is administered by veterinarians to the domestic animal. This vaccine is not suitable for human use.
Humans can contract the disease by contact with B. anthracis. endospores or vegetative cells. The disease cannot be transmitted from person-to-person through either contact or through coughing, etc., therefore, the disease is said not to be contagious. There are three different forms of anthrax and the same organism causes all three of the various forms of disease. The difference in disease expression is entirely dependent upon which region of the body the organism infects. There are several possibilities which are:
1. Cutaneous Anthrax
The first and least deadly (with antibiotic treatment) form of anthrax
is a skin infection known as cutaneous anthrax. The organism can be
picked up by handling an infected animal that has died, an animal that may
have the endopores caught in its hair or present on its skin. Or, the
endospores may be contacted on surfaces. Such spores may exist for years
(decades is the estimate) unless surfaces are cleaned with agents that
kill bacterial endospores. The endospores can enter the skin through
tiny abrasions or cuts, revert to a vegetative cell
and begin to divide and produce an extremely harmful, tissue-killing
toxin (comprised of three different proteins). The first signs of
cutaneous anthrax might be the appearance of a rash on the hand, arm
or neck, soon after exposure, and additionally, conditions symptomatic of
more common illnesses (fever, aches, irritability, etc.). After awhile -
days perhaps, depending on the number of organisms that gained entry into
the skin, an obviously infected area would appear. This area would
initially show as a raised, inflamed bump - at first looking somewhat
like an insect bite, and later would appear as a watery, pustule with a
black center. The black center appears because the tissue in the
central area of the infection, died (necrosis). This form of anthrax
illness is the mildest form of the disease but does require antibiotic
treatment to clear the infection. In the absence of antibiotic
treatment (penicillin, doxycycline or ciprofloxacin or others) about
twenty percent of those with cutaneous anthrax will die.
2. Gastrointestinal Anthrax
Another form of the disease is known as gastrointestinal anthrax.
This form of the disease, caused by B. anthracis can be acquired
from eating imprpperly cooked contaminated meat prepared from animals
that are infected with the organism or through the drinking of water
contaminated with endospores of the organism. Symptoms of intestinal
anthrax may include fever, vomiting of blood, diarrhea and severe stomach
and intestinal (abdominal) cramps. Antibiotics are effective against this
form of the disease also if treatment is received quickly (within days of
infection). However, 20 to 60 percent of those with gastrointestinal
anthrax may die.
3. Inhalation Anthrax
The most dangerous form of the disease caused by B. anthracis
affects the lower resporatory system (lungs) and is known as inhalation
anthrax. To acquire this form of disease, it is estimated that one must
inhale between 2,500 to 10,000 (some upper estimates are 55,000)
endospores into the lower part (alveolar regions)of the lungs in order for
the infection to become established. To be inhaled into the lungs, the
size of the endospore is very important. The endospore must be between 1
micrometer (millionths of a meter) and 5 micrometers in diameter, and no
larger in order for the particle to enter the alveolar spaces deep inside
the lungs. If the particle is larger than 5 micrometers in diameter
the cilia - the hair-like appendages in the throat and bronchial airways -
will trap the particle and sweep the particle up and out of the lungs.
Once the spores are inhaled, over a relatively short period of time (days to weeks, depending on the person and number of spores inhaled) the disease kills approximately ninety percent of its victims. If antibiotic therapy is administered immediately after infection, there is a reasonable chance for survival. Unfortunately, respiratory anthrax is very dangerous not only beccause of the location and effect of the toxin produced, but also because of a similarity of initial symptoms of illness. The initial symptoms appear much like the flu. Consequently, unless one suspects exposure to this organism, there may be a delay in seeking treatment. The flu cannot be treated with antibiotics, because the flu is caused by a virus - not a bacterium. This delay can subsequently lead to a lack of ability to effectively treat the infection with antibiotics. Within a few days in the absence of antibiotic therapy severe symptoms would appear, lungs would fill with fluid, and breathing would become difficult. By this time, a person would likely have only a day or two to live.
Before the use of anthrax to terrorize and harm individuals in the United States after September 11, 2001, there had been only approximately 18 cases of inhalation anthrax recorded in the U.S. over the past approximately 100 years. Obviously, before the outbreak of anthrax over the past several months, there was little if any previous familiarity among the medical community with the symptoms of this form of anthrax.
It is important to realize that no matter what form of the disease that is exhibited, the disease is not contagious - meaning that after someone contracts the illness the disease is not spread from person to person. There must be direct contact with the organism. Therefore, unless the vegetative or endospore form of the organism enters through an abrasion or wound in the skin, is inhaled or is ingested, a person nearby an infected person will not contract the disease.
There is a vaccine for humans that protects against anthrax. This vaccine is apparently relatively effective in preventing the cutaneous form of the disease. This vaccine may be effective against the other forms of the disease, i.e., gastrointestinal and inhalation anthrax. However, because it is not ethical to test the vaccine in human subjects against these relatively more dangerous forms of the disease, the ability of this vaccine to protect humans from intestinal and respiratory anthrax is not presently known.
The Web Site of the Centers for Disease Control and Prevention (CDC) located in Atlanta, Georgia has a substantial amount of highly useful and well-written information on anthrax and many other infectious diseases. Please See: Anthrax Information at the CDC. Additionally, the HomePage of the CDC may lead one to further information regarding governmental response initiatives. Please See: Official CDC Web Site.
Additionally, the following link will lead you to a 1999 Consensus Statement concerning Anthrax that was generated by a committee charged with investigation of the potential use of anthrax as a biological weapon. This extremely informative and well-written statement provides substantial, detailed information concerning anthrax. Please see: Journal of the American Medical Association (JAMA), Volume 281, Number 18, pages 1735-1745, May 12, 1999 - Consensus Statement - Anthrax as a Biological Weapon.
Germs Book: Don't Touch That Doorknob!