Updated: 7/11/2021

Anthrax

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Snapshot
  • A 40-year-old farmer from rural China presents to a local hospital for fever and cough. He reports to have had a nonproductive cough for a few days and feels more short of breath and lightheaded this morning. He works frequently with sheep on the countryside. On physical exam, his temperature is 102.2°F (39.0°C), blood pressure is 100/70 mm Hg, pulse is 96/min, and respirations are 22/min. On physical exam, there is bilateral rhonchi in the lung bases. Chest radiograph reveals a widened mediastinum and bilateral infiltrates.
Introduction
  • Classification
    • Bacillus anthracis
      • spore-forming and exotoxin-forming gram + rod
      • capsule protects against phagocytosis 
        • the only bacterial with polypeptide capsule (poly-D-glutamate) 
    • transmission
      • inhalation of spores
      • direct contact of spores to a skin break
      • ingestion of spores
  • Epidemiology
    • incidence
      • more common in areas where animal vaccination rates are low
      • bioterrorism
    • risk factors
      • intravenous drug use (e.g., heroin)
      • occupational exposure to unvaccinated animals
      • occupational exposure to animal hides
  • Pathogenesis
    • edema toxin performs the same function as adenylate cyclase, ↑ cAMP and results in
      • black eschar with edematous borders
      • vasodilation and hypotension
    • infection may spread via lymphatics
  • Associated conditions
    • cutaneous anthrax
      • most common
    • pulmonary anthrax
      • “woolsorter’s disease”
    • gastrointestinal anthrax
  • Prevention
    • post-exposure prophylaxis
      • 3 doses of anthrax vaccine
      • 60 days of a single antibiotic
        • ciprofloxacin or doxycycline are first line
  • Prognosis
    • biphasic nature of pulmonary anthrax
      • prodromal symptoms
      • fulminant bactermic phase
        • often leads to death within days
Presentation
  • Symptoms
    • pulmonary anthrax
      • flu-like syndrome with non-productive cough
      • nausea and vomiting
      • hemoptysis
      • chest pain
    • gastrointestinal anthrax
      • nausea and vomiting
      • dysentery
      • abdominal pain
  • Physical exam
    • cutaneous anthrax
      • initial lesion is a painless and pruritic papule with central vesicle or bulla
      • this progresses to painless and necrotic black eschar
        • surrounded by edema
      • eschar sloughs off at day 14
    • pulmonary anthrax
      • mediastinitis
      • shock
      • hypoxia
      • dyspnea
    • lymphadenopathy
Imaging
  • Chest radiography
    • indication
      • pulmonary anthrax
    • findings
      • pleural effusion
      • pulmonary consolidation
      • widened mediastinum
Studies
  • Labs
    • multiple methods of detection
      • “medusa head” appearance on microscopy
        • halo of projections
      • culture of blood, pleural fluid, or eschar
      • positive Gram stain of affected tissue
        • box-car like appearance
      • polymerase chain reaction
      • anti-protective antigen immunoglobulin G on enzyme-linked immunosorbent assay
      • biopsy with immunohistochemistry staining
    • marked hemoconcentration
  • Making the diagnosis
    • most cases are diagnosed clinically and confirmed with
      • positive culture, serology, or immunohistochemistry
      • detection of Bacillus anthracis DNA in tissue
Differential
  • Community-acquired pneumonia
    • distinguishing factor
      • less likely to have nausea, vomiting, pallor, or unexplained mediastinal widening on chest radiography
Treatment
  • Management approach
    • antibiotics should be given in the prodromal phase of the disease
    • cutaneous anthrax can be treated with 1 antibiotic
    • systemic anthrax can be treated with 2 antibiotics
  • Medical
    • ciprofloxacin or doxycycline 
      • indication
        • all patients
      • doxycycline adverse effects
        • gastrointestinal upset, photosensitivity, teeth discoloration, and inhibition of bone growth in children
        • photosensitivity 
      • ciprofloxacin adverse effects
        • gastrointestinal upset, risk of tendon rupture, and QT prolongation
    • protein synthesis inhibitor
      • indications
        • systemic anthrax
        • combination therapy with fluoroquinolone or doxycycline
      • mechanism
        • reduces toxin production
      • drugs
        • clindamycin
        • linezolid
    • antitoxins
      • indication
        • all patients
      • drugs
        • monoclonal antibodies
          • raxibacumab
        • anthrax immunoglobulin
Complications
  • Bacteremia from cutaneous anthrax
  • Death

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