Anthrax (Bacillus anthracis)

Early diagnosis of anthrax and initiation of appropriate treatment, particularly administration of a combination of antimicrobial drugs, are critical to improving survival

About

• Anthrax is the Greek word for coal, in reference to the black skin lesions victims develop in a cutaneous skin infection.
• Anthrax is due to bacillus anthracis and is a zoonotic infection usually acquired from herbivores and their hides.

Characteristics

• It is gram +ve and aerobic and forms spores
• Capsulated which consists of a polypeptide or D-Glutamic acid when in vivo

Source

• Found in soil from infected carcasses, wools, hides, bones
• It is most commonly an infection of animals but can be passed to man
• Animals are vaccinated in the US where thye have had previous anthrax
• Areas where found endemically
  • Central/South America
  • Sub-Saharan Africa,
  • Asia, South/Eastern Europe
  • Caribbean.

Virulence - Toxin production and capsule

• Protective antigen, a protein that binds to cells and forms channels and allows LF and EF to enter cells
• Lethal factor (LF) - a protease of Mitogen-activated protein kinase (MAP kinase)
• Oedema factor (EF) a calmodulin activated adenylate cyclase
• These factors tend to produce marked oedema and haemorrhage
• Antiphagocytic capsule

Pathophysiology

Microscopy

Clinical Pathogenicity

• Cutaneous
  • Infection via skin abrasions from Hides and bones to form a black eschar with a localised haemorrhagic lymphadenitis
  • Often seen with people handling hides in dock workers where spores got through abraded skin to cause a local and then systemic response
• Inhalational (Mortality> 50%)
  • 'Wool sorters disease' with SOB, fever, shock, chest pain
  • Also could be form of bioterrorism
  • Progressive cyanosis, hypoxia, effusions and widened mediastinum on CXR
  • Develops a haemorrhagic mediastinitis and shock
• Gastrointestinal
  • Due to ingestion of meat products
  • Nausea, Vomiting, Abdominal pain and bloody diarrhoea
  • May cause progressive symptoms and even death
• Shock/Sepsis
  • Hypotension ,renal failure, Microangiopathic haemolytic anemia
  • Coagulopathy, thrombocytopenia, and haemorrhage
  • Meningitis and hemorrhagic brain parenchymal infection

Investigations

• Isolation of the organism - Spores seen with modified Ziehl Nielsen stain
• McFadyean's reaction demonstrates bacilli in blood by heat fixing with polychrome methylene blue showing blue bacilli and surrounding pink capsular debris
• Serology for capsular antigen
• CXR: mediastinal widening
• CT chest: mediastinal involvement

CXR showing mediastinal widening

CXR several hours before death

Among patients with inhalation anthrax antimicrobial drug combination therapy was more likely to be curative than antimicrobial drug monotherapy

Management: Discuss with Infectious Diseases early

• Prevention: There is a vaccination available for those at high risk of infection
• ABC, ITU Supportive, Oxygen, Antibiotics (Ciprofloxacin, Levoflxacin, Doxycycline) combined with aminoglycoside
• Benzyl Penicillin if susceptible and given early enough
• Cephalosporins are contraindicated due to resistance
• Antitoxin (raxibacumab or anthrax immunoglobulin)
• Drainage of pleural effusions, Consideration of IV Dexamethasone
• Prophylactic Ciprofloxacin to contacts

References

• Centers for Disease Control and Prevention Expert Panel Meetings on Prevention and Treatment of Anthrax in Adults