Bacillus Anthracis

Epidemiology

  • Causes both human and animal disease
  • Endemic worldwide

Exposure

  • Military/Bacterial Warfare: may produce either cutaneous or inahlational anthrax
  • Goat Hair:
  • Wool: inhalational anthrax is also known as “woolsorter’s disease”
  • Animal Hide Exposure:

Etiology

  • Bacillus anthracis Infection
    • Large spore-forming gram-positive rod
    • CDC Category A Agent: potential to be easily disseminated, have higher contagiousness, have high morbidity and mortality, and require increased public health preparedness

Physiology

  • Transmission and Mechanism: inhalation of 3-5 ยต Bacillus anthracis spores into alveoli
    • Spore engulfment by macrophages -> carried to hilar (regional) nodes -> multiplication of organism in its vegetative state in hilar and mediastinal nodes (where anthrax toxin is produced)
    • High-Grade Bacteremia may result with production of 3 toxins (protective antigen, edema factor, lethal factor)
      • Protective factor binds to cell surface and facilitates endocytosis of edema and lethal factors
      • Toxin released into circulation causes septic shock
  • Anti-Phagocytic Capsule: enhances lethality
  • Estimated LD50: 2500-55k inhaled spores (although as few as 1-3 spores may cause disease in some reported cases in 2001)
  • Incubation Period: 6 days (may vary with level of exposure)
    • Accidental release in Sverdlovsk: incubation period was as long as 100 days

Diagnosis

  • Sputum GS/Cult+Sens:
  • CXR/Chest CT patterns:
    • Mediastinal Widening (due to mediastinal adenopathy and/or hemorrhagic mediastinitis):
    • Patchy, Non-Segmental Infiltrates:
    • Unilateral or Bilateral Pleural Effusion:
  • Blood c/s: frequently positive in <12 hrs, if antibiotics have not been given
    • Level A hospital labs: can isolate the organism from routine cultures and provide presumptive identification
    • Level B hospital labs: can confirm
  • PCR and Specific Antigen Staining Assays: available from CDC

Clinical Presentations

Cutaneous Anthrax

  • Epidemiology: most common presentation
  • Clinical
    • Pruritic Vesicles/Papules: ultimately develop into ulcers -> eschars
    • Regional Lymphadenopathy: accompanies rash

Inhalational Anthrax (Woolsorter’s Disease)

  • Epidemiology: rare presentation (only 18 cases reported in US in the 20th century)
  • Clinical
    • Flu-Like Symptoms (fever, headache, malaise, dry cough, abdominal discomfort): occur for first few days
      • Typical flu symptoms like rhinorrhea and sore throat are uncommon
      • Absence of severe bronchospasm
      • Biphasic Presentation (makes diagnosis difficult): patient may transiently improve without therapy, but will usually deteriorate after that with respiratory symptoms
    • Hematogenous Dissemination Stage (acute): dyspnea/cyanosis/tachycardia/septic shock/fever
      • Rapidly fatal within 24 hrs of hematogenous dissemination (unless treated): survival is related to time from onset of symptoms to start of antibiotics
    • Pleural Effusion: present in all of the recent cases in 2001
    • Hemorrhagic Mediastinitis:
    • Acute Lung Injury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]])
    • CNS Infection (50% of cases): hemorrhagic meningitis/SAH
  • Prognosis
    • Historical Case-Fatality Rate: 80-100%
    • Recent Case-Fatality Rate: 45% (presumably better due to rapid diagnosis and treatment)

GI Anthrax

  • Epidemiology: very rare (has never been diagnosed in US)

Treatment

  • Cipro + Clinda: notably, clinda inhibits toxin production
    • Alternative: doxy + clinda
    • Vanco or Rifampin: may be added to cover CNS infection
    • Need to check antibiotic sensitivities, as weaponized anthrax may have altered sensitivities
    • All anthrax strains are resistant to Cephalosporins and some have an inducible penicillinase
  • Infection Control: standard precautions (no human-to-human transmission, regardless of type of anthrax)
  • Prophylaxis: prophylaxis of close contacts is not required
  • Anthrax Vaccine: available
    • Acellular, contains protective antigen
    • SE: mild in 63% of recipients, severe in <1% of recipients
    • Pre-Exposure Regimen: 6 injections over 18 mo period with annual boosters
  • Post-Exposure Prophylaxis: 3 doses of vaccine + antibiotics (cipro or doxy) x 30 days
    • Alternative: cipro
    • Alternative: doxy x 60-100 days
    • Alternative: amox x 60-100 days (for pregnant women and children

References

  • Shafazand S, Doyle R, Ruoss S. Inhalational anthrax: epidemiology, diagnosis, and management. Chest 1999; 116:1369-1376
  • Franz D, Jahrling P, Friedlander A, et al. Clinical recognition and management of patients exposed to biological warfare agents. JAMA 1997; 278:399-411
  • Pile J, Malone J, Eitzen E, et al. Anthrax as a potential biological warfare agent. Arch Int Med 1998; 158:429-434
  • Inglesby T, Henderson T, Bartlett J, et al. Anthrax as a biologic weapon: medical and public health management. JAMA 1999; 281:1735-1745
  • Dixon T, Meselson M, Guillemin J, et al. Medical progress: anthrax. N Engl J Med 1999; 341:815-826