ACMT Toxicology Visual Pearl: The Black Eschar

Answer: 1. Bacillus anthracis

This patient has cutaneous anthrax. Anthrax is a serious infectious disease caused by gram positive, rod shaped, bacteria known as Bacillus anthracis [1]. B. anthracis spores are very resistant to environmental factors including physical and chemical inactivation and can persist in the environment for a prolonged period of time. Human illness is most commonly acquired by handling animal fluids or pelts. There are several forms of anthrax, however cutaneous is the most common (95% of cases) and the least complicated to treat [2].

What are the symptoms of cutaneous anthrax? [3, 4]

• Naturally occurring cases develop after spores of B. anthracis are introduced subcutaneously, often secondary to contact with infected animals or animal products.
• Mortality: 25% (untreated) vs <1% (treated)
• Incubation period: 5-7 days (range 1-12 days)
• Rash progression:
  • Begins as a small painless but pruritic papule and quickly enlarges
  • Lesion develops a central vesicle or bulla, which erodes, leaving a painless necrotic ulcer with a black, depressed eschar
  • The eschar will usually slough off in 1-2 weeks.
• Systemic symptoms: May include fever, malaise, and headache

Making the diagnosis [5]

• Patient history and clinical suspicion are key in making the diagnosis.
• Confirmation can be obtained by culturing the lesion, serologic testing, or punch biopsy.

Is cutaneous anthrax reportable? [6, 7]

• Anthrax is a reportable diagnosis.
• Patients suspected of having anthrax should have their disposition and treatment determined in conjunction with your Infectious Disease specialists and your state health department.
• Notify the CDC via the National Notifiable Disease Surveillance System.

Treatment [6, 7]

• Antimicrobial therapy for cutaneous anthrax without systemic symptoms – treat for 7-10 days
  • Ciprofloxacin 500 mg PO every 12 hours OR
  • Doxycycline 100 mg PO every 12 hours OR
  • Levofloxacin 750 mg PO every 24 hours OR
  • Moxifloxacin 400 mg PO every 24 hours
• Vaccination [6, 7]
  • Anthrax vaccine adsorbed (AVA) is licensed for pre-exposure prophylaxis for adults at high risk for anthrax exposure (i.e., military personnel, laboratory staff working with anthrax, professions that handle animals or animals’ hides/products)
  • Vaccination should be administered as part of treatment for cutaneous anthrax
• Adjunctive therapies
  • Raxibacumab and obiltoxaximab (monoclonal antibodies) and anthrax immunoglobulin may be considered in other forms of anthrax, such as inhalational anthrax [7, 8].
  • Glucocorticoid therapy should be considered in anthrax meningitis, cutaneous anthrax with extensive tissue edema involving the head and neck, or anthrax with vasopressor-resistant shock [9].

When should you administer post-exposure prophylaxis (PEP)? [6,10]

• PEP is unlikely to be indicated for naturally occurring cutaneous anthrax.
• ED providers are only exposed in these cases if they have direct contact with drainage from open wounds while not using PPE or there is concern for aerosolization of spores
• For inhalational anthrax exposure, AVA should be given in combination with antimicrobials (ciprofloxacin or doxycycline) for 60 days.

Clinical Pearls

• Anthrax is a rare but life-threatening infection
• Diagnosis is made from a through history and physical and confirmatory testing.
• Prompt diagnosis and therapy with antimicrobials significantly reduce mortality.
• Involve your infectious disease specialists and state health department in cases of suspected anthrax.