Anthrax

This disease is notifiable in the UK under the Public Health (Infectious Diseases) Regulations 1988

Anthrax is a bacterial infection caused by the Gram-positive, spore forming, bacteria Bacillus anthracis. Spores are very resistant to damage and can remain dormant in the soil for decades. It is primarily a disease of herbivorous mammals. The disease occurs most often in wild and domestic animals in Asia, Africa and parts of Europe. Humans generally acquire the disease through contact with infected animals or contaminated animal products.¹

• Cutaneous anthrax: direct contact with the skins or tissues of infected animals, e.g. among people working with animal products, such as hides from abroad.
• Inhalation anthrax: breathing in anthrax spores, usually in industrial processes such as the tanning of animal skins, and processing of wool or bones from abroad.¹
• Intestinal anthrax: very rare; occurs from swallowing spores in contaminated meats.
• Person-to-person infection is very rare. Airborne transmission from one person to another does not occur and skin infection from direct contact with anthrax lesions is uncommon.
• Incubation period: with inhalation anthrax, symptoms usually develop within 48 hours of exposure, but some cases of skin anthrax may not appear for days or weeks.¹

• Bioterrorism: terrorists may use anthrax as a 'biological weapon' by releasing large quantities of spores in an aerosol.¹
• The threat is considered serious as the organism is relatively easy to cultivate from environmental sources and the inhalation form of disease has a high mortality rate.¹

There are three forms of the disease depending on the mode of infection:

• Cutaneous: (95% of cases):¹
  • Usually hands, forearms, face and neck.
  • 2-3 days after exposure an inflamed itchy pimple develops, which enlarges and becomes vesicular and then ulcerates, and 2-6 days later a black eschar develops - 'Malignant pustule'.
  • Local erythema and induration, with local lymphadenopathy.
  • Oedema may be striking and there may be hepatosplenomegaly.
  • Associated systemic malaise with headache and sore throat, but often afebrile.
  • Contact with skin lesions can transmit cutaneous infection.
• Inhalation: Pulmonary anthrax: ID50 (ID50 is the dose required to infect 50% of exposed individuals) for inhalation anthrax is approximately 10,000 spores.
  • Initially flu-like illness with a non-productive nausea, vomiting, sore throat, cough, sweats, fever, confusion, headache, and myalgia.
    Also develop pallor or cyanosis, dyspnoea, tachycardia, abdominal pain, pleuritic chest pain
  • Abrupt onset of respiratory failure may develop 2-4 days later.
  • Antibiotic treatment (see below) should be given immediately after exposure (in the prodromal stage), as they may not prevent a fatal outcome if delayed until pulmonary or bacteraemic symptoms develop.
• Ingestion:
  • Rare - characterised by severe abdominal pain, nausea and vomiting with watery or bloody diarrhoea.
  • If bacteraemia develops it is usually fatal, with massive gastrointestinal haemorrhage and sometimes meningoencephalitis.

• Gram stain is characteristic (Gram positive rod) in cultures from skin or nasal swabs (best sent dry - to prevent germination of other organisms) or from blood cultures.
• Further investigations for cutaneous anthrax may include biopsy of skin lesion for immunohistochemical staining, and serology.
• Further investigations for inhalation or ingested anthrax:
  • Chest x-ray: often a widened mediastinum is present (lymphadenopathy and haemorrhagic mediastinitis), pleural effusion, pulmonary infiltrates
  • Full blood count: raised white cells (predominantly neutrophils)
  • Liver function tests: raised transaminases

• Consult most recent updated guidelines for treatment at the PHLS website¹ and immediately contact local Hospital Infection Control Team.
• Antibiotics will need to be continued for 60 days if a case of deliberate release is suspected and inhalation of spores may have occurred.
• Inhalation or ingestion:
  • Should be treated initially with either ciprofloxacin (initially intravenously) or doxycycline combined with one or two other antibacterials (e.g. rifampicin, vancomycin, amoxicillin, benzylpenicillin, chloramphenicol, clindamycin, imipenem, gentamicin).
  • When the condition improves and the sensitivity of the Bacillus anthracis strain is known, treatment may be switched to a single antibacterial.
  • Treatment should continue for 60 days because germination may be delayed.
• Cutaneous:
  • Should be treated with either ciprofloxacin or doxycycline for 7 days. First choice is ciprofloxacin until sensitivity testing is available.
  • Treatment may be switched to amoxicillin if the infecting strain is susceptible.
  • Treatment may need to be extended to 60 days if exposure is due to aerosol.
  • A combination of antibacterials for 14 days is recommended for cutaneous anthrax with systemic features, extensive oedema, or lesions of the head or neck.

• Oral ciprofloxacin 500mg bd for 60 days. Second line: doxycycline.
• Only those directly exposed to spores (not their contacts) need prophylaxis.
• Ciprofloxacin has the added advantage that it is also the first line prophylactic treatment for other potential agents that may be used in deliberate release scenarios such as plague and tularaemia.
• In certain circumstances, post exposure vaccine may be indicated - discuss with Public Health Laboratory Service.

• Vaccination against anthrax is available and is recommended for those at highest risk, e.g. those handling dead animals such as abattoir workers and laboratory staff.
• Immunization of animals at risk, and enforcement of sound food-handling and carcass-hygiene policies.²