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Causative Agent

Bacillus anthracis

  • Aerobic, gram-positive, rod-shaped, encapsulated and spore-forming bacterium

Incubation Period

1 - 6 days (up to 30 days)

Infectious Period

Articles and soil contaminated with spores can remain infective for decades.


A zoonotic disease mainly of herbivorous animals; transmitted by direct  contact with B. anthracis-infected animal tissues or products from infected animals i.e. drums, or with anthrax spores in soil. Humans are generally incidental hosts.

Anthrax in human is not considered contagious; person-to person transmission of cutaneous anthrax has rarely been reported.

Three forms exist:

  • Cutaneous anthrax: As a result introduction of the spore through the skin (especially via abrasions).
  • Gastrointestinal anthrax: As a result of ingestion of infected tissues.
  • Inhalation anthrax: As a result of inhaling spores aerosolized by industrial processing of contaminated materials i.e. hides, among persons working with contaminated animal skin or bioterrorism.


Most common in agricultural regions in Central and South America, sub-Saharan Africa, Central and Southwestern Asia and Southern and Eastern Europe.

Three main forms of disease:

  • Cutaneous: Usually manifests as a black, necrotic skin lesion.
  • Gastrointestinal: Rare, but highly fatal form that occurs after ingestion of contaminated meat.
  • Inhalational: Most lethal form (mortality > 80%) that occurs following inhalation of spores.
  • Cutaneous anthrax:
    • Case fatality <1% with antimicrobials (up to 20% untreated).
    • haracterized by localized itching, followed by painless papule, which turns vesicular and enlarges, ulcerates, and develops into a depressed black eschar usually surrounded by edema; commonly involve the head, neck, forearms and hands.
    • May have satellite lesions with regional lymphadenopathy, associated fever and headache.
  • Gastrointestinal anthrax:
    • Case fatalities are <40% with treatment (>50% untreated).
    • May present in either intestinal or oropharyngeal forms.
    • Causes rapid onset abdominal pain with haemorrhagic ascites and shock and death may occur within 2-5 days of onset.
  • Inhalation anthrax:
    • Case fatalities ~45% with aggressive treatment (generally >85%).
    • Biphasic illness, with initial phase characterized by non-specific flu-like illness (fever, malaise, fatigue, cough, mild chest discomfort) followed by acute phase characterized by acute respiratory distress and sepsis.
    • May present as acute haemorrhagic mediastinitis.
    • Hemorrhagic meningitis may result from hematogenous spread.

  • Suitable specimens as indicated include blood cultures, cerebrospinal fluid, sputum, lymph node biopsy, peritoneal fluid, stool or rectal swab for gastrointestinal anthrax, and sub-eschar material and vesicular fluid for cutaneous anthrax. Please contact the laboratory in advance to discuss the most appropriate workup.
  • Nasal swabs are only for supporting a confirmed exposure to B. anthracis or epidemiological studies and are not recommended for routine investigation without specific advice from MOH.
  • Gram stain may show typical Gram-positive bacilli occurring singly or in short chains often with squared off ends (safety-pin appearance).
  • CXR: widened mediastinum without infiltrates in previously healthy patient in the absence of trauma is pathognomonic for anthrax.
  • PCR-contact MOH
  • Environmental testing-contact MOH

Treatment should be initiated as soon as diagnosis is suspected. Antibiotic administration at the earliest signs of disease is essential. Ciprofloxacin or doxycycline should be considered an essential part of first-line therapy for inhalational anthrax. Combination antimicrobial therapy is recommended for inhalational anthrax infection.


  • IV ciprofloxacin 400 mg 12 hourly empirically or
  • IV doxycycline 100 mg 12 hourly (if available) plus
  • One or two additional agents: rifampicin, vancomycin, chloramphenicol, imipenem, clindamycin or clarithromycin.
  • All patients should be given the anthrax vaccine if available. Antibiotic treatment should be continued until three doses of vaccine have been administered (day 0, 14 and 28). If vaccine is unavailable, antibiotic treatment should be continued for 60 days.


  • IV ciprofloxacin 20-30 mg/kg/day bd (not to exceed 1g/day) or
  • IV doxycycline 2.2 mg/kg 12 hourly for patients < 45 kg; adult dose if > 45 kg
  • One or two additional agents (as for adults above).
  • Continue antibiotic treatment for 60 days.

  • Prophylaxis should be provided to all persons who may have been directly exposed to the spores. It is critical to administer chemoprophylatic antibiotics as soon as possible after potential exposure. Contacts i.e. family, friends, healthcare providers do not require prophylaxis unless they too had been exposed to the spores.
  • Oral ciprofloxacin 500 mg bd is the recommended first line medication in a situation with anthrax as the presumptive agent.
  • Alternatives: oral doxycycline 100 mg bd or amoxicillin 500 mg 8 hourly if the strain is sensitive.
  • For children, oral ciprofloxacin 20-30 mg/kg/day bd (max 1 gm/day), doxycycline 2.2 mg/kg/day bd (max 100 mg bd), amoxicillin 80mg/kg/day tds (max 500 mg tds).
  • Oral antibiotic prophylaxis should be continued for at least 60 days.
  • If vaccine is available, all exposed persons should be vaccinated with three doses of anthrax vaccine (days 0, 14, 28).

Notify MOH immediately on suspicion. Call MOH Communicable Diseases Surveillance team at: 98171463

An inactivated cell-free product is available (not locally). The vaccine efficacy against cutanoeus anthrax has been documented for humans; evidence for protection against inhalational and gastrointestinal anthrax is limited to animal studies.

  • Standard precautions.
  • After an invasive procedure or if autopsy is performed, the instruments and the area used should be thoroughly disinfected with a sporicidal agent such as 0.5% sodium hypochlorite.
  • No quarantine is needed.


  1. CDC (Atlanta) informational website. Available at Accessed Jan 2011.
  2. WHO.          Anthrax          in          humans          and          animals,          4th          edition,          2008: Guidelines 2008/en/index.html. Accessed Jan 2011.

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