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Copyright 2005 Tara K. Harper.  All rights reserved.

TKH Bacteriology Notes:
Anthrax -- updated!

 Description        Mechanism        Outbreaks
 Vector        Symptoms        Vaccine
       Diagnosis        Odds 'n' Ends
       Treatment        Links and Images

Science and Literary  Links for Writers
Science and Technical  References for Writers


NOTE:  This file is for information only.  It is not intended for diagnosis.


Anthrax
Also Known As:
       Woolsorter's disease
       Woolsorter's pneumonia
       Ragsorter's disease

Description.  Anthrax is caused by the gram-positive, aerobic spore-forming bacteria, Bacillus anthracis.  The disease is marked by effusions of blood and fluids in various organs and body cavities and by symptoms of extreme prostration.  Animal anthrax primarily affects herbivores.  Human anthrax usually results from cutaneous infection caused by the handling of infected animal hides, hair, fur, bone, or wool.  In rare circumstances, human anthrax results from ingestion or inhalation of the spores from contaminated animal products.  Anthrax is considered a pathogen which can be relatively easily and widely distributed and is a potential agent of biological warfare.  The spores can remain dormant but viable for decades.

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Vector.   In its infectious form, anthrax is a spore that usually populates the soil but which, in rare cases, can become airborne and inhaled.  With cutaneous anthrax, the bacteria infects the host through direct penetration of the host skin.  

Anthrax is different from many pathogenic organisms in that it appears to depend on the death of its host in order to propagate.  Once the host is dead and the host body begins decaying, the bacteria in the bloodstream are exposed to oxygen.  These bacteria turn into spores which populate the surrounding soil and can be taken up by herbivores either through ingestion or cutaneous infection.  

Anthrax does not appear to be transmissable from  person to person.

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Mechanism.   Anthrax bacteria infect the bloodstream, where they multiply profusely.  The toxins produced by the bacteria circulate in the bloodstream and produce a variety of effects on the host.  

It is thought that one of the ways anthrax kills its host is by destroying immune cells called macrophages.  These macrophages would mediate the harmful effect of the toxic protein  (LF, or, lethal factor) produced by the anthrax bacteria.  It is possible, however, that the macrophages themselves, in excessive concentrations as a result of the anthrax infection, are responsible for some of the shock and other toxic reactions of anthrax victims.  

Another possibility is that LF is not just a protein, but a protease--an enzyme that cuts other proteins.  If so, the LF toxins might cleave and inactivate enzymes in important cell-signalling pathways, crippling the body's ability to grow new cells and replace damaged tissues.

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Symptoms.  There are four forms of anthrax:  cutaneous, intestinal, pulmonary (inhalatory anthrax), and cerebral.  


     

Cutaneous anthrax.  This form of anthrax is severe and is most common.  Cutaneous anthrax causes lesions, which presents first as an itchy papule that resembles an insect bite.  The papule becomes a hemorrhagic vesicle (a blister) which bursts and discharges a bloody serum.  Within 36 hours, the blister forms a hard but painless, blue-black leathery scab of necrotic tissue, usually 1-3 cm in diameter.  The absence of pain is characteristic of anthrax lesions.  Lymph glands close to the wound might swell. Constitutional symptoms are:  high fever, vomiting, profuse sweating, and extreme loss of strength and exhaustion.  Approximately 20% of untreated cases of cutaneous anthrax are fatal.  CDC images of cutaneous anthrax.

Intestinal anthrax.  Patients present first with chill, high fever and with pain in the head, back and abdomen, and extremities.  Additional initial symptoms include vomiting, vomiting blood, bloody diarrhea, and prostration.  Often, mucous membranes and the skin will hemorrhage. Intestinal anthrax results in death 25% to 60% of the time.

Pulmonary anthrax.  Usually caused by the inhalation of dust containing the anthrax spores.  Patients present initially with symptoms similar to the common cold. These symptoms include or progress to:  initial chill, followed by pain in the back and legs, fever, rapid breathing and rapid pulse, shortness of breath, cough, vomiting, and extreme prostration.  Pulmonary anthrax usually results in death 1-2 days after the onset of acute symptoms.  CDC images of inhalational anthrax.

Cerebral anthrax.  Cerebral anthrax is a secondary result of intestinal or pulmonary anthrax, and it occurs when the anthrax bacilli also invade the capillaries of the brain.  Patients with cerebral anthrax present with the symptoms of pulmonary or intestinal anthrax, but also experience violent delerium which is often associated with hemorrhagic meningitis.

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Diagnosis.  Diagnosis can be made by either of these methods:
   1.  Isolating B. anthracis from the blood, skin lesions, or respiratory secretions
   2.  Measuring specific antibodies in the blood

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Treatment.  Primarily high-dose penicillin and isolation.  Other treatments and antibiotics include:  cephalosporin, chloramphenicol, anti-anthrax globulin, corticosteroids, osmoregulatory solutions, erythromycin, and tetracycline.   Prophylactic tetracycline has been used for some exposed populations.

However, although antibiotics kill the anthrax bacteria, by the time characteristic symptoms appear, the bacteria are multiplying wildly in the bloodstream.  The massive amounts of toxin produced by these bacteria circulates throughout the bloodstream and cannot be eliminated by killing the bacteria. Antibiotics do not affect the circulating toxin.

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Outbreaks and History of Infection

Spring, 1979, epidemic in Sverdlovsk, Union of Soviet Socialist Republics; human and animal anthrax outbreak.   Anthrax was confirmed in both human and animal populations in a narrow zone about 4 km long, extending from a military microbiology facility into the southern part of the city, Sverdlovsk, and following the path of the northerly wind that prevailed shortly before the outbreak.  In all, 96 cases of human anthrax and 64 human deaths were reported.  Animal anthrax was confirmed in sheep and cows in six villages in the outbreak zone.  

Epidemiological and pathoanatomical evidence confirm that all fatal human cases were caused by an inhaled form of the pathogen.  Although the Soviet Union initially (1979, 1980) claimed that the outbreak was gastrointestinal (79 cases) or cutaneous (17 cases), Western analysts believed that the anthrax pathogen had escaped in aerosol form from the military facility.  In May, 1992, President Boris Yeltsin confirmed that "the KGB admitted that our military developments were the cause" of the 1979 outbreak of anthrax.  The Sverdlovsk outbreak is the largest documented outbreak of human anthrax caused by inhalation.

September, 2001, USA, terrorist attacks using a combination of biological (anthrax) and physical (jet airliner) weapons against numerous targets.

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Vaccine.  Various vaccines exist, including:
     - ST1:  a live, nonencapsulated spore vaccine
     - A cell-free (dead bacteria) filtrate vaccine, which is reported to be 93% effective against cutaneous anthrax.

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Odds 'n' Ends.  Cutaneous anthrax on the neck is an occupational hazard of hide porters.

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Links:
       Anthrax Q&A - CDC 's FAQ on anthrax.
       Anthrax diagnosis and evaluation - CDC fact sheets, information, web casts, etc. on signs and symptoms.
       Images of cutaneous anthrax and inhalation anthrax.
       Risk of Anthrax in Animals - Clear, easy to understand information from a veterinary site.
       Anthrax in Livestock and Animals - Dept. of Agriculture, Colorado.


Copyright 2005Tara K. Harper

All rights reserved.  It is illegal to reproduce or transmit in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, any part of this copyrighted file without permission in writing from Tara K. Harper.  Permission to download this file for personal use only is hereby granted by Tara K. Harper.


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