black eschar anthrax

Which of the following is the most likely explanation for this skin lesion in a worker handling sheep hides?

  1. Bacillus anthracis
  2. Group A streptococcus
  3. Pseudomonas aeruginosa
  4. Staphylococcus aureus

(Photo credit: CDC/ James H. Steele, Public domain via Wikimedia Commons)

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.

References

  1. Klein F, et al. Pathophysiology of anthrax. J Infect Dis (1966): 123-138. DOI: 10.1093/infdis/116.2.123
  2. Goel AK. Anthrax: A disease of biowarfare and public health importance. World J Clin Cases. 2015;3(1):20-33. doi:10.12998/wjcc.v3.i1.20
  3. Kamal SM, Rashid AK, Bakar MA, Ahad MA. Anthrax: an update. Asian Pac J Trop Biomed. 2011 Dec;1(6):496-501. doi: 10.1016/S2221-1691(11)60109-3. PMID: 23569822; PMCID: PMC3614207.
  4. Simonsen KA, Chatterjee K. Anthrax. [Updated 2022 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.
  5. Chambers J, Yarrarapu SNS, Mathai JK. Anthrax Infection. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.
  6. CDC. Anthrax. Accessed on April 16, 2023.
  7. Savransky V, Ionin B, Reece J. Current Status and Trends in Prophylaxis and Management of Anthrax Disease. Pathogens. 2020;9(5):370. Published 2020 May 12. doi:10.3390/pathogens9050370
  8. Vietri, Nicholas J.. Does anthrax antitoxin therapy have a role in the treatment of inhalational anthrax?. Current Opinion in Infectious Diseases 31(3):p 257-262, June 2018. | DOI: 10.1097/QCO.0000000000000446
  9. Hendricks KA, Wright ME, Shadomy SV, et al. Centers for disease control and prevention expert panel meetings on prevention and treatment of anthrax in adults. Emerg Infect Dis. 2014;20(2):e130687. doi:10.3201/eid2002.130687
  10. Anthrax in Humans and Animals. 4th edition. Geneva: World Health Organization; 2008. 7, Treatment and prophylaxis. Accessed May 1, 2023.
Alex Blackwell, MD

Alex Blackwell, MD

Resident
Department of Emergency Medicine
Carolinas Medical Center
Alex Blackwell, MD

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Kathryn T. Kopec, DO

Kathryn T. Kopec, DO

Associate Professor of Emergency Medicine
Medical Toxicologist
Carolinas Medical Center