The Bug
Anthrax is an acute infectious disease caused by the spore-forming
bacterium Bacillus anthracis. Anthrax most commonly
occurs in herbivorous animals (cattle, sheep, goats, camels,
antelopes), plant eating animals that normally graze for food,
and can be transmitted to humans by direct contact with infected
animals and animal products (hides, hair and wool).
There are no known cases of human-to-human transmission of
the infection. Blood and body fluids of infected individuals
are not infectious.
Anthrax can enter the body through skin, by inhalation of
the spores, or by ingestion of contaminated animal products
(undercooked meat). Whatever the portal of entry, the symptoms
are due to the actions of three toxins produced by the bacterium,
namely edema factor, lethal factor and protective antigen.
Due to the rapid course of inhalation disease, early diagnosis
and intervention with antibiotics are essential in the management
of cases of suspected inhalation anthrax.
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The Centers for Disease Control and Prevention (CDC) has
identified anthrax as a high priority potential biologic agent.
High-priority agents include organisms that have some of the
following characteristics:
- Can be easily disseminated or transmitted
person-to-person
- Cause high mortality
- Might cause public panic and social disruption
- Require special action for public health
preparedness
Anthrax cannot be transmitted from person to person. However,
it can be grown easily in large quantities. Its spores are
resistant to destruction, and can theoretically be aerosolized
to reach large areas and numbers of people. However, despite
these feature, anthrax has never been successfully used as
a biological weapon, perhaps due to the large numbers of bacterial
spores required for infection and to the impact of environmental
conditions on successful dissemination of spores.
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Anthrax is part of normal soil flora. It is endemic in Iran,
Iraq, Turkey, Pakistan and sub-Saharan Africa as well as some
areas of South and Central America. Anthrax also continues
to cause infections in animals in the developed word. For
instance, between 1963 and 1992, nine epizootics of anthrax
occurred in bison herds in northern Alberta and the Northwest
Territories, and outbreaks of anthrax occurred in cattle in
both France and Australia in 1997. Anthrax spores can remain
dormant for decades and are resistant to drying, heat, ultraviolet
light, gamma radiation and many disinfectants. For these reasons,
surface decontamination of the bacillus in endemic countries
is considered impractical.
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Anthrax is primarily a disease of herbivores, with human
infection occurring as a result of accidental contact or ingestion
of infected products. Most cases of human anthrax are related
to skin contact with or inhalation of anthrax spores associated
with cleaning contaminated goat hair (thus the name woolsorters'
disease), or contact with textiles manufactured from contaminated
goat hair. There has been a significant reduction in the incidence
of anthrax with decreased use of imported, contaminated raw
material and immunization of textile workers. Anthrax is rare
in developed countries primarily because the disease has been
controlled in animals through vaccination. Those who work,
or are exposed to infected animals and products in countries
where anthrax is endemic, may be at increased risk of contracting
the disease. This would include veterinarians, animal handlers,
abattoir workers, laboratory workers, and those in the textile
industries that are involved in animal hair processing.
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Soil contaminated by anthrax spores can infect grazing animals.
The infection is then transmitted to humans through direct
contact with infected animal tissues or the consumption of
contaminated meat. The use of raw materials contaminated with
anthrax spores in the manufacturing industry supports a reservoir
for human infection through either direct contact or inhalation
of spores.
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