PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Anthrax is a rare but serious bacterial infection caused by the Gram-positive, spore-forming, bacterium 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. Symptoms usually develop within two days of exposure for inhalation anthrax and 1-7 days with cutaneous anthrax.
Anthrax in drug users
Anthrax in drug users appears to be very rare. However, since December 2009, a significant number of heroin users in Scotland have been found to have anthrax infection. There have also been similar cases reported in England. Anthrax has probably been contracted by taking heroin contaminated by anthrax spores. Heroin or the cutting agent mixed with heroin may become contaminated with anthrax spores, which can then be injected, smoked, or snorted.
- Cutaneous anthrax: direct contact with the skins or tissues of infected animals - eg, 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.
- Intestinal anthrax: very rare and is caused by swallowing spores in contaminated meats.
- Injection anthrax: since December 2009, anthrax infection has been identified in a a signficant number of drug users in Scotland, probably contracted from using heroin contaminated by anthrax spores.
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.
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Deliberate release of anthrax
- Bioterrorism: terrorists may use anthrax as a 'biological weapon' by releasing large quantities of spores in an aerosol.
- 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.
- Anthrax is uncommon. The Health Protection Agency (HPA) report that in England and Wales only 21 possible cases of anthrax were notified between 1981 and 2009.
- However, since December 2009 there has been an ongoing outbreak of anthrax among heroin users in the UK.
- In Scotland, between December 2009 and December 2010, there were 119 drug-using patients who were classed as anthrax cases. 14 of these cases died.
- There have been reports in other areas of England and, in December 2012, a further case of anthrax in a heroin user was confirmed in Medway, Kent.
- Infections are more common in countries where the disease is common in animals - eg, South and Central America, southern and eastern Europe, Asia, and Africa.
Typically, there are three forms of the disease, depending on the mode of infection. However, 'injection anthrax' can be considered to be a fourth disease form characterised by soft tissue infection.
Cutaneous: (95% of cases):
- 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.
- 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, there is a 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 'Treatment', 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.
- 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.
- Soft tissue infection may present as swelling, redness and pain around injection sites.
- Abscess or ulcers at an injection site, often with marked oedema.
- Possible late presentation with septicaemia and meningitis.
- As well as antimicrobials, prompt surgical management of the soft tissue infection is likely to be needed for good outcomes.
Anthrax in drug users
The presentation depends on the way in which the heroin is taken by the user. Most commonly this leads to injection anthrax but symptoms of inhalational anthrax may occur if contaminated heroin has been smoked.
The HPA provides an algorithm for the clinical evaluation and management of drug users with possible anthrax. 
Laboratory staff should be warned of possible anthrax in specimens so that appropriate laboratory biohazard precautions can be followed.
- FBC shows raised white cells (predominantly neutrophils); LFTs 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.
- CXR 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.
Inhalation or gastrointestinal anthrax:
- Treat initially with either ciprofloxacin or doxycycline combined with one or two other antibiotics - eg, 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.
- 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.
- Timely surgical debridement is important to remove primary source of toxin.
- Empirical antibiotics to cover B. anthracis as well as other causes of soft tissue infections are needed.
- This can involve a five-drug combination - intravenous ciprofloxacin and clindamycin with penicillin, flucloxacillin and metronidazole.
- 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.
- Anthrax immunisation is indicated for individuals at high risk of occupational exposure. These include those who handle infected animals, for those exposed to imported infected animal products, and for laboratory staff who work with B. anthracis .
- A four-dose regimen is used for primary immunisation; booster doses should be given annually to workers at continued risk of exposure to anthrax.
- 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). 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.
Further reading & references
- Notifications of Infectious Diseases (NOIDs); Public Health England
- Shooting Up: Infections among people who inject drugs in the UK 2011. An update: November 2012; Health Protection Agency.
- Anthrax, Health Protection Agency
- Anthrax, Health Protection Scotland.
- Case of anthrax in Medway, Health Protection Agency
- Hicks CW, Sweeney DA, Cui X, et al; An overview of anthrax infection including the recently identified form of disease in injection drug users. Intensive Care Med. 2012 Jul;38(7):1092-104. doi: 10.1007/s00134-012-2541-0. Epub 2012 Apr 24.
- Clinical guidelines for the assessment and management of anthrax, Health Protection Agency
- Cunha BA; Anthrax, Medscape, Dec 2012
- British National Formulary
- Immunisation against infectious disease - the Green Book (latest edition); Public Health England
- 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.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Colin Tidy
Dr Euan Lawson
Dr Helen Huins