Anthrax is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • A highly infectious disease caused by the bacteria Bacillus anthracis that primarily infects ruminant animals (cows, goats, and sheep). Cutaneous (95% of United States cases), inhalational, and GI forms cause human disease.
  • Synonym(s) for cutaneous anthrax: charbon; malignant pustule; Siberian ulcer; malignant edema; splenic fever; Milzbrand
  • Synonym(s) for inhalational anthrax: ragpicker disease; woolsorter disease

Epidemiology

  • Total of 235 anthrax cases (224 cutaneous and 11 inhalational) occurred in the United States between 1955 and 1994, resulting in 20 fatalities.
  • Cutaneous: 95% of cases in the United States; cutaneous anthrax without history of appropriate exposure risk raises concern for bioterrorism.
    • 5–20% of untreated cases result in death; case fatality rate is <1% with antibiotic therapy.
  • GI: very rare in the United States
    • Mortality rate is estimated to be 25–60%.
  • Inhalational anthrax is rare in the United States. In absence of occupational exposures to animal hides or products, cases of inhalational anthrax should be considered bioterrorism until proven otherwise.
    • 99% of untreated cases result in death. Fatality rates are still 45–80% in patients with severe symptoms who are treated in state-of-the-art medical facilities.
    • From October to November 2001, 11 cases of inhalational anthrax and 11 cases of cutaneous anthrax resulted from the bioterrorist release of B. anthracis along the east coast of the United States.
  • “Injectional anthrax” B. anthracis as a pharmaceutical contaminant; >50 recognized cases occurred in the United Kingdom between December 2009 and December 2010, with 33% fatality rate.
  • Anthrax is most common in agricultural regions of the Middle East, Asia, Southern and Eastern Europe, Africa, South and Central America, and the Caribbean.

Etiology and Pathophysiology

  • B. anthracis is a soil-based, spore-forming, gram-positive bacterium found worldwide; anthracis derived from Greek word for “coal,” describing characteristic black cutaneous lesions
  • B. anthracis has three known virulence factors: an antiphagocytic capsule and two protein toxins (edema factor and lethal factor)
    • The capsule provides resistance to phagocytosis.
    • A protective antigen protein binds to host cell surface. After protease cleavage, a binding site is created for lethal factor and edema factor; protective antigen is required for the action of these two protein toxins.
  • B. anthracis spores are phagocytosed at the exposure site by macrophages where they germinate into vegetative forms and produce virulence factors.
  • Cutaneous anthrax occurs when B. anthracis enters the skin through a cut or abrasion during the handling of infected animal products (e.g., meat, wool hides).
  • GI: ingestion of contaminated meat
  • Inhalational: inhalation of aerosolized spores (1 to 2 μm diameter)

Risk Factors

  • Contact with infected animals/animal products
  • Bioweapon/bioterrorism: military, mail handlers, response workers
  • Travelers to endemic areas with appropriate exposure
  • Drug users

General Prevention

  • Vaccine protects against all forms of anthrax. The vaccine causes minimal local reactions, no long-term sequelae, and is effective against naturally occurring and biologically engineered strains (1)[A].
  • Vaccine has been established as safe by the FDA, the CDC, and the National Academy of Sciences.
  • Vaccine schedule: 5 IM doses at 0, 4 weeks; and 6, 12, and 18 months with annual boosters. IM (vs. SC) route reduces the incidence of local adverse events.
    • Anthrax vaccine adsorbed (BioThrax) is FDA-approved for ages 18 to 65 years; pregnancy Category D
    • If behind schedule, do not restart series; pick up where left off (delays do not diminish protection).
    • Individuals are not protected until they have completed the full series.
    • The most common adverse reactions are tenderness, pain, erythema, and a temporary limitation of arm motion at the site of injection (~10%). The most common systemic reactions are muscle aches, fatigue, and headache (~5%).
    • The Advisory Committee on Immunization Practices (ACIP) recommends vaccination for (2)[C]:
      • Laboratory personnel working with B. anthracis
      • Persons working with imported animal hides or furs in areas with insufficient measures to prevent exposure to anthrax spores
      • Persons who handle potentially infected animal products in high-incidence areas
      • Military personnel deployed to areas with high risk for exposure to biologic warfare
      • Pregnant women should be vaccinated only if absolutely necessary.
  • Proper public health and first responder preparation can limit exposure (3)[C].

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Citation

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TY - ELEC T1 - Anthrax ID - 116038 Y1 - 2019 PB - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116038/all/Anthrax ER -