Infection¹

• 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.
• Injection anthrax: since December 2009, a signficant number of drug users in Scotland have been found to have anthrax infection, probably contracted from using heroin contaminated by anthrax spores.
• Intestinal anthrax: very rare and is caused by 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.

Deliberate release of anthrax

• 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

Epidemiology¹

• Anthrax is uncommon in the UK and only 21 possible cases of anthrax were notified between 1981 and 2008.
• However, since December 2009 there has been an ongoing outbreak of anthrax among heroin users in the UK.
• Infections are more common in countries where the disease is common in animals, e.g. South and Central America, southern and eastern Europe, Asia, and Africa.

Presentation

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

• Cutaneous: (95% of cases):¹
  • Usually hands, forearms, face and neck.
  • Usually 2-3 days after exposure (but there may be a much longer incubation) 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.
  • Symptoms usually develop within 48 hours of exposure.
  • Initially flu-like illness with a nonproductive nausea, vomiting, sore throat, cough, sweats, fever, confusion, headache, and myalgia. Patients also develop pallor or cyanosis, dyspnoea, tachycardia, abdominal pain, and 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 it 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.

Anthrax in drug users

The presentation depends on the way in which the heroin is taken but anthrax may present with:¹

• Swelling and redness at an injection site, which may be painful.
• Abscess or ulcer at an injection site, often with marked oedema.
• Septicaemia.
• Meningitis.
• Symptoms of inhalational anthrax.

Diagnosis²

Laboratory staff should be warned of possible anthrax in specimens so that appropriate laboratory biohazard precautions can be followed.

• Full blood count shows raised white cells (predominantly neutrophils); liver function tests show raised transaminases.
• The diagnosis of cutaneous anthrax is usually suggested by the characteristic appearance of skin lesions.
• B. anthracis may be cultured from the ulcer or eschar (in cutaneous anthrax), pleural fluid, the cerebrospinal fluid (CSF) or the blood. Specimens may be stained or cultured to demonstrate the organism. B. anthracis readily grows on blood agar, and staining microbiologically differentiates the organism from non-B. anthracis bacilli.
• The preferred diagnostic procedure for cutaneous anthrax is staining the ulcer exudate with methylthioninium chloride (methylene blue) or Giemsa stain (mixture of methylene blue and eosin).
• Blood cultures may be indicated if cutaneous anthrax is associated with fever and other systemic symptoms.
• Chest X-ray and/or chest CT scan are indicated if inhalation anthrax is suspected. CXR often shows a widened mediastinum (lymphadenopathy and haemorrhagic mediastinitis), pleural effusion and pulmonary infiltrates.
• Enzyme-linked immunosorbent assay (ELISA) serological diagnosis is also available.

Treatment

Consult the most recently updated guidelines for treatment at the Health Protection Agency website¹ and immediately contact the local Hospital Infection Control Team. Current treatment recommendation:³

• Inhalation or gastrointestinal anthrax:
  • Treat initially with either ciprofloxacin or doxycycline combined with one or two other antibiotics, e.g. amoxicillin, benzylpenicillin, chloramphenicol, clarithromycin, clindamycin, imipenem with cilastatin, rifampicin and vancomycin.
  • When the condition improves and the sensitivity of the B. anthracis strain is known, treatment may be switched to a single antibiotic. Treatment should continue for 60 days because germination may be delayed.
• Cutaneous anthrax:
  • Treat with either ciprofloxacin or doxycycline for 7 days (treatment may need to be continued for 60 days if exposure is due to aerosol).
  • Treatment may be switched to amoxicillin if the infecting strain is susceptible.
  • A combination of antibacterials for 14 days is recommended for cutaneous anthrax with systemic features, extensive oedema or lesions of the head or neck.

Prognosis

• Cutaneous anthrax is readily treatable with antibiotics if diagnosed early.
• Mortality is often high for inhalation and gastrointestinal anthrax because of delayed diagnosis and also the lack of readily available treatment in developing countries.

Prevention

• Anthrax immunisation is indicated for individuals who handle infected animals, for those exposed to imported infected animal products, and for laboratory staff who work with B. anthracis.³
• A 4-dose regimen is used for primary immunisation; booster doses should be given annually to workers at continued risk of exposure to anthrax.³
• Post-exposure immunisation may be indicated, in addition to antibiotic prophylaxis. Ciprofloxacin or doxycycline should continue for 60 days (may be switched to amoxicillin after 10-14 days if the strain of B. anthracis is susceptible).³ Vaccination against anthrax may allow the duration of antibacterial prophylaxis to be shortened.
• Immunisation of animals at risk, and enforcement of sound food-handling and carcass-hygiene policies.⁴

Document references

1. Anthrax, Health Protection Agency
2. Cunha BA; Anthrax. eMedicine, Aug 2008.
3. British National Formulary; 59th Edition (March 2010) British Medical Association and Royal Pharmaceutical Society of Great Britain, London (link to current BNF)
4. George S, Mathai D, Balraj V, et al; An outbreak of anthrax meningoencephalitis. Trans R Soc Trop Med Hyg. 1994 Mar-Apr;88(2):206-7. [abstract]

Internet and further reading

• Notifications of Infectious Diseases (NOIDs), Health Protection Agency

Acknowledgements