is a large Gram-positive, endospore-producing
bacillus. In clinical specimans it typically appears singly or in pairs;
in culture it appears as a streptobacillus.
- While endospores
appear in culture, they are not seen in clinical specimans.
- A facultative
- B. anthracis primarily
- Contact with infected animals,
animal materials, infected soil, or B. anthracis endospores used
as a bioweapon.
- B. anthracis primarily
infects herbivores (def);
humans are usually accidental hosts.
- Rare in developed countries but
more prevalent in underdeveloped countries where animals are vaccinated against
- There are three forms of anthrax:
cutaneous, inhalation, and gastrointestinal. Around 95% of human anthax infections
in nature are the cutaneous form as a result of B. anthracis endospores
entering exposed skin.
- Cutaneous anthrax first appears
as a painless papule (def)
at the site of infection and rapidly progresses to an ulcer (def)
surrounded by vesicles (def)
and finally a necrotic eschar (def).
The mortality rate from untreated cutaneous anthrax is approximately 20%.
- Inhalation anthrax may initially
have an asymptomatic latent period of two months or more. Typically, alveolar
engulf the inhaled endospores of B. anthracis and transport them
to the mediastinal lymph nodes (def)
where they can germinate. Initial symptoms are nonspecific and include coughing,
headache, fever, chills, vomiting, and chest and abdominal pain. This rapidly
worsens and presents as worsening fever, edema, and massive enlargement if
the mediastinum (def).
About half of infected individuals have symptoms of meningitis (def).
Almost all cases progress to shock (def)
and death within about three days of the initial symptoms. This is the most
deadly form of anthrax.
- Gastrointestinal anthrax as a
result of ingestion of B. anthracis can appear two ways: ulceration
of the mouth and esophagus (def)
followed by localized lymphadenopathy (def),
and sepsis (def)
if the bacterium invades the upper intestinal tract; and nausea, vomiting,
and malaise (def)
rapidly progressing to sepsis if the bacterium invades the large intestines.
by Burke A Cunha, MD, Professor of Medicine, State University of New York at
Stony Brook School of Medicine; Chief, Infectious Disease Division, Vice-Chair,
Department of Internal Medicine, Winthrop-University Hospital.
Kaiser's Microbiology Home Page
Copyright © Gary E. Kaiser
All Rights Reserved
Updated: Feb. 23, 2005
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