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Anthrax
Anthrax is an acute bacterial
infection caused by a an organism called Bacillus anthracis. It is
mainly a disease of herbivorous animals.
Humans
become infected when spores of B. anthracis are introduced into
the body by:
In
human beings the most common form of this infection is Cutaneous
Anthrax. It is characterized as a localized skin lesion with a central
eschar surrounded by marked edema or swelling.
Other
forms are more dangerous -
Inhalation
Anthrax (woolsorters' disease) - it involves hemorrhagic mediastinitis,
rapidly progressive systemic infection, and a very high mortality rate.
Gastrointestinal Anthrax is rare and is also
associated with a high mortality rate.
Clinical Manifestations of Anthrax
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Bacillus anthracis |
| The distribution of anthrax
is worldwide. All animals are susceptible to varying degrees,
but the disease is most prevalent among domestic herbivores
(including cattle, sheep, horses, and goats) and wild
herbivores. Grazing
animals become infected when they are foraging for food in areas
contaminated with spores of B. anthracis. Anthrax
in herbivores tends to be severe, with a high mortality rate.
Terminally ill animals have overwhelming bacteremic infections
and often bleed from the nose, mouth, and bowel, thereby
contaminating soil or watering places with vegetative B.
anthracis that can subsequently sporulate and persist in the
environment. The carcasses of infected animals provide
additional potential foci of contamination. Biting flies have
also been implicated as vectors for the spread of anthrax,
and vultures that feed on infected carcasses occasionally spread
spores from a contaminated area to noncontiguous areas, probably
by the contamination of surface water pools. |
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B.
anthracis is
a large (1 to 1.5 um by 4 to 10 um), nonmotile, encapsulated,
chain-forming, aerobic, gram-positive rod that forms oval
spores. Oxygen is required for sporulation but not for
germination of spores, and sporulation does not take place in
living animals. The rectangular shape of the individual bacteria
gives chains of B. anthracis a boxcar-like appearance.
Spores of B. anthracis can survive for years in dry earth
but are destroyed by boiling for about 10 min, by treatment with
oxidizing agents such as potassium permanganate or hydrogen
peroxide, or by dilute formaldehyde. Most strains of B.
anthracis are susceptible to penicillin. |
The
natural resistance of humans to anthrax
is greater than that of herbivorous animals. Agricultural cases result
most often from contact with animals that have anthrax
(for example, during skinning, butchering, or dissecting), from bites of
contaminated or infected flies, and (in rare instances) from consumption
of contaminated meat. Industrial cases are associated with exposure to
contaminated hides, goat's hair, wool, or bones.
Anthrax
in animals has been a long-standing problem in Iran, Turkey, Pakistan,
and Sudan, and the probability is high that animal products (especially
goat's hair) originating from these areas will be contaminated with anthrax
spores.
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Outbreaks of Anthrax |
- Only
three cases of cutaneous anthrax
were reported in the United States from 1984 through 1993.
Very recently after the September 11, 2001 WTC attack a
couple of cases of anthrax were reported at Florida. The
exact nature of these cases is still under investigation.
- Large
epidemics of anthrax
occurred in the former Soviet Union at Sverdlovsk in 1979
- In Zimbabwe between 1978 and
1985, largest epidemic occurred when more than 10,000
human cases had been recorded, nearly all of them of
cutaneous variety.
- In
India, anthrax disease was commonly reported among the
tribal communities of Karnataka, Andhra Pardesh, Orissa
and West Bengal. In an outbreak of this disease very
recently six weeks ago two persons had died of anthrax in
Alagurkhi village of Kolar district in Karnataka, that
also took a toll of 230 sheep, an ox and 2 cows.
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Clinical Manifestations of Anthrax
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Anthrax
as Biological Weapon
Back to Biological Weapons
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