- Clinical science
Anthrax is a rare, infectious disease caused by Bacillus anthracis, a gram-positive spore-forming bacterium that is found in soil. Human infection usually results from contact with infected livestock or infected animal products (e.g., wool or meat). B. anthracis spores have also been weaponized for biological warfare/terrorism. Depending on the route of entry, three distinct clinical syndromes can occur: inhalation anthrax, cutaneous anthrax, and gastrointestinal anthrax. Cutaneous anthrax (the most common form) presents initially as a papular lesion, which later becomes vesicular, and eventually forms a necrotic eschar. Inhalation anthrax results in hemorrhagic mediastinitis and presents with fever, acute, nonproductive cough, retrosternal chest pain, and/or pleural effusion. Gastrointestinal anthrax, which is very rare, causes gastrointestinal ulceration, which results in hematemesis and/or bloody diarrhea. The diagnosis of anthrax is confirmed by the microscopic evidence of B. anthracis. Mortality is high but swift treatment with antibiotics (e.g., fluoroquinolones, linezolid, meropenem) can increase survival. Prognosis of cutaneous anthrax is usually better than that of inhalation and gastrointestinal anthrax.
- Pathogen: Bacillus anthracis
- Human infection occurs following exposure to B. anthracis or its spores, usually as a result of contact with infected animals or infected animal products (e.g., wool, hide, meat)
- Weaponized anthrax: infection resulting from exposure to weaponized anthrax spores (from an act of bioterrorism or biological warfare)
- Person-to-person transmission typically does not occur.
- The clinical manifestations of anthrax depend on the site of entry of B. anthracis. (see “Clinical features” below)
Anthrax infection is an occupational hazard for people who handle livestock and process potentially infected animal materials such as wool or meat.
- Antiphagocytic capsule (containing poly-D-glutamate)
Anthrax toxin: responsible for the local and systemic manifestations of anthrax
Anthrax toxin is made up of A and B subunits.
- B subunit binds to endothelial receptors → the B subunit facilitates entry of the A subunit into the host cell.
- The A subunit has 2 components:
- Anthrax toxin is made up of A and B subunits.
Depending on the route/mechanism of infection, one or more of three anthrax subtypes may occur.
|Cutaneous anthrax||Inhalation anthrax|
|Relative frequency|| || || |
Route of entry
| || || |
|Incubation period|| || || |
Systemic spread commonly occurs in inhalational anthrax and gastrointestinal anthrax. It less common in cutaneous anthrax (5–10% of cases).
|Cutaneous anthrax||Inhalation anthrax||Gastrointestinal anthrax|
Samples to collect
|Pathogen detection|| |
Diagnosis of anthrax infection can be made if either the confirmatory test or at least two of the supportive microbiologic tests indicate an infection.
|Treatment||Cutaneous anthrax||Inhalation anthrax||Gastrointestinal anthrax|
|Causative||Without systemic spread||-||-|
|With systemic spread|
|Specific|| || |
|Lethality|| || || |
While gastrointestinal anthrax and inhalational anthrax are rare, they have a particularly poor prognosis, even with antibiotic treatment!
- AVA (anthrax vaccine adsorbed) is the only FDA-approved vaccine that is available for active immunization against anthrax in the US.
- AVA is contraindicated among children < 18 years, adults > 65 years, and pregnant/lactating women. In these groups, antitoxin therapy with raxibacumab, obiltoxaximab, or anthrax immunoglobulin is indicated instead of AVA.