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.
- Global distribution: Anthrax is endemic in agricultural regions of the USA, Canada, Central and South America, southern and eastern Europe, central and southwest Asia, and sub-Saharan Africa.
- Incidence: 0–2 cases per year
- Sex: ♂ > ♀
Epidemiological data refers to the US, unless otherwise specified.
- Pathogen: Bacillus anthracis
- Human infection occurs following exposure to B. anthracis or its spores (e.g., inhalation), usually as a result of contact with infected animals or infected animal products (e.g., wool, hide, meat).
- Bioterrorism or biological warfare: exposure to weaponized B. anthracis or its spores. An attack using aerosolized anthrax could infect a large number of individuals and cause many casualties, especially if an antibiotic-resistant strain was used.
- Person-to-person transmission is rare, but cases of person-to-person transmission of cutaneous anthrax have been reported.
Anthrax infection is an occupational hazard for people who handle livestock and process potentially infected animal materials such as wool or meat.
- Antiphagocytic capsule
Anthrax toxin: responsible for the local and systemic manifestations of anthrax; made up of A and B subunits
- The A subunit has 2 components:
- The B subunit (PA; anthrax toxin protective antigen); binds to endothelial receptors and facilitates entry of the A subunit into the host cell.
Depending on the route/mechanism of infection, one or more of three anthrax subtypes may occur.
|Overview of anthrax subtypes|
|Feature||Cutaneous anthrax||Inhalation anthrax (Woolsorters' disease)||Gastrointestinal anthrax|
|Relative frequency|| || || |
Route of entry
| || || |
|Incubation period|| || || |
|Diagnostics of anthrax|
|Cutaneous anthrax||Inhalation anthrax||Gastrointestinal anthrax|
Samples to collect
|Treatment of anthrax|
|Type of treatment||Cutaneous anthrax||Inhalation anthrax||Gastrointestinal anthrax|
|Antibacterial||Without systemic spread||-||-|
|With systemic spread|
|Specific|| || |
- AVA (anthrax vaccine adsorbed) is the only FDA-approved vaccine that is available for active immunization against anthrax in the US.
- AVA is contraindicated in 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.