Bacillus Anthracis

Characteristics/Epidemiology

Enzootic disease - endemic to a population of animals (occurrences changes little over time)

Affect mainly domestic herbivores - sheeps, goats, and horses

Pathogenesis/Transmission

Transmitted to human by contaminated dust or infected animal products.

Infection usually started by subcutaneous inoculation of spores.

Less frequently, by inhalation.

1. Capsule

Antiphagocytic - essential for full virulence

Polymer of D-glutamic acid - not immunogenic by itself

2. Exotoxin

Antigenic - stimulate antibodies.

2.1. Oedema factor

Causes elevation of intracellular cAMP

Causes severe oedema

2.2. Lethal toxin

Clinical significance

1. Cutaneous anthrax

95% of human cases.

20% mortality if untreated.

Progression

Introduction of spore

-> papule

-> painless black severely swollen "malignant pustule"

-> (in some cases) invasion of regional lymph nodes

-> (in some cases) invasion of general circulation (fetal septicaemia)

2. Pulmonary anthrax (woolsorter's disease)

Inhalation of spores.

Progressive haemorrhagic lymphadenitis

Almost 100% mortality if untreated.

3. Gastrointestinal form

Ingestion of spores.

Occurs most often in animals.

Laboratory identification

Blunt-ended bacilli.

Spores are oval and centrally located.

Colonies on blood agar: large, grayish, non-hemolytic, irregular border.

Extreme caution due to aerosol transmission.

Direct immunofluorescence assay can help in identification.

Treatment

First line: penicillin G, doxycycline, ciprofloxacin

Effective in cutaneous anthrax only when used early.

Prevention/immunity

Autoclaving is the most reliable means of decontamination due to resistance of the spores.

Cell-free vaccine is also available.

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Things to revise/add later:

Bibliography: LWW microbiology

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