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Quick Reference
Environment: ubiquitous,
soil-borne pathogen
Microorganism: Gram
+ rod
Spore former: YES
Motile: NO
Susceptibility: anyone
Communicability: rarely infectious
Exposure: skin exposure to spores, inhalation, ingestion
Incubation: 1-50 days
Primary Treatment: antibiotics and hospital care
Prognosis: cutaneous, good with treatment; pulmonary, usually fatal
Quarantine recommended: NO
Use as a biological weapon: YES
Identification
Anthrax or
woolsorter's disease is an acute
infectious disease caused by the spore-forming bacterium, Bacillus anthracis.
Though common primarily in livestock, humans and other animals are also susceptible
to infection. Anthrax is most common in agricultural areas of Africa, the
Middle East, Central and South America, and Asia. The disease is rare in
the United States with only 18 cases reported during the 1900s.
B. anthracis is a large, Gm+ aerobic, non-motile,
endospore-forming rod occurring in chains. The spores are resistant to many disinfectants,
but are found to be susceptible to 2% glutaraldehyde formaldehyde and 5%
formalin.
Laboratory indications:
- Non-hemolytic (blood agar)
- Non-motile
- Gel hydrolysis -
- Catalase +
Pathogenesis
Infection can occur three ways, cutaneous, inhalation, and
gastrointestinal. B. anthracis spores are extremely resilient and
may remain naturally viable in the soil for decades. Humans are most
commonly infected by handling diseased animals or by inhaling
spores.
Virulence factors are an edema toxin, lethal toxin and a
capsular polypeptide antigen, D-glutamic acid. With cutaneous infection, the
organism enters through a break in the skin and multiply, producing a
necrotizing toxin. Even with effective therapy started early, the
hemorrhagic lesion still develops and sloughs off. When dust particles
containing spores are inhaled,
the organisms are deposited in the terminal alveoli where they are
engulfed by macrophages and transported to the lymph nodes. Once in the lymph
nodes, vegetative cells multiply and produce toxin causing extensive
necrotic hemorrhaging. Exact pathogenesis of gastrointestinal infection is
not known, but bacteria invade intestinal mucosa where they colonize and
produce toxins.
Manifestations
The incubation period varies depending upon how the disease was contracted, but
generally, symptoms appear within seven days of infection.
Cutaneous infection accounts for most cases of anthrax, about 95%. The
bacterium enters via open lesions or cuts in the skin. Symptoms appear
with a raised bump that may resemble an itchy insect bit, but progresses
to an ulcer surrounding necrotic tissue in the center. Though fatalities
are rare when treated with antibiotics, if left untreated, death occurs in
about 20% of cutaneous anthrax cases.
Pulmonary anthrax, caused by inhalation of spores, is probably the most
serious form of the disease as it is usually fatal. An infectious dose
would require inhalation of roughly 8,000-50,000 organisms. Initially, symptoms
resemble those of a common cold, but gradually progress to breathing difficulty
and eventual shock. Death occurs in nearly 100% of cases.
Intestinal anthrax usually results from consuming tainted meat from
animals that carry the disease. This very rare form is characterized by acute
inflammation of the gastrointestinal tract. Early symptoms include
appetite loss, nausea, vomiting, and fever, but are followed by severe
abdominal pain, vomiting of blood, and diarrhea. Death occurs in 25% to
60% of cases.
Treatment
Anthrax is not highly contagious and, therefore, is rarely spread from
person-to-person. The only known cases of transmission are with the
cutaneous form. The disease is initially diagnosed by isolating B.
anthracis from blood, skin lesions, or respiratory secretions. Further
testing requires measuring levels of antibodies in the blood of
individuals suspected to have the disease.
Antibiotics are used to treat
anthrax, with penicillin being preferred, however ciprofloxacin,
tetracylines, erythromycin, doxycycline, and chloramphenicol are also
used. Treatment should be initiated early; if the disease is left
untreated or if symptoms are allowed to progress, it can be fatal.
Prevention
Due it's potential as a weapon of biological warfare, all active duty
U.S. military personal involved in potential conflicts are vaccinated
against the disease. The vaccine is a cell-free filtrate and is 93%
effective in preventing the disease. Immunization consists of three
injections, given two weeks apart. Three additional subcutaneous
injections are given at the sixth, twelfth, and eighteenth months. Annual
boosters of the vaccine are highly recommended.
If traveling or residing in countries where anthrax is common in
livestock, avoid direct contact with the animals and ensure that meat has
been properly slaughtered and adequately cooked.
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