Anthrax: guidance for testing
Information on clinical features and laboratory testing, including environmental testing.
Background
Anthrax is a rare infection caused by the bacteria Bacillus anthracis. This is a large, spore-forming, Gram-positive bacillus. By forming spores, the bacteria can survive in harsh conditions such as dry environments and can persist in the soil for many decades. Spores begin to germinate when they are exposed to a nutrient-rich environment, such as the tissues or blood of an animal or human host.
Anthrax in humans is very rare in the UK and has largely been associated with imported contaminated animal products. The most significant UK outbreak in humans was of injectional anthrax in 2009 to 2012 associated with the use of contaminated heroin.
The clinical presentation and incubation period of anthrax depend on the route of transmission. There are 4 major clinical syndromes:
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Cutaneous anthrax – infection is established once the bacterial spores enter through a break in the skin, often as a result of contact with contaminated meat or animal products. Subcutaneous injection of drugs contaminated with spores can also lead to cutaneous anthrax. The infection starts as a painless papule at the site of entry, then develops into an oedematous, vesicular lesion often surrounded by satellite lesions. This will then erupt into the characteristic necrotic ulcer with an overlying eschar.
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Inhalation anthrax – occurs when anthrax spores are aerosolised while handling contaminated animal products or working in contaminated environments. The organism is taken into the bloodstream by macrophage cells, where the spores germinate as vegetative bacteria. The bacteria reproduce rapidly and produce toxins that destroy host cells. The bacteria can then spread in the bloodstream, reaching high numbers in the blood as well as causing local damage with fluid leakage into the lungs and very enlarged mediastinal lymph nodes. The lymph nodes may rupture and bleed into the lungs causing pulmonary haemorrhage. Smoking infected heroin may also cause this form of anthrax.
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Gastrointestinal (GI) anthrax – occurs following ingestion of contaminated animal products and causes ulceration and extensive oedema throughout the gut. It usually presents with fevers, nausea, vomiting, abdominal pain and bloody diarrhoea. Gastrointestinal haemorrhage can also occur secondary to severe gastric ulceration. Oropharyngeal anthrax is a subtype of GI anthrax, caused by the ingestion of contaminated products. This causes a more localised infection presenting with severe sore throat, fever, dysphagia and cervical lymphadenopathy.
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Injectional anthrax – occurs following intramuscular or intravenous injection of contaminated drugs. Intramuscular injection, known as ‘popping’, can cause local infection, which may be limited or may cause significant swelling and tissue damage, or progress to sepsis and death. Intravenous injection is highly likely to cause fatal infection. Note that a similar picture can be seen with infections from environmental organisms such as Clostridium novyi which can also contaminate heroin during preparation.
Anthrax meningitis may also be seen. It is very rare and may occur without a clear route of entry. Secondary anthrax meningitis occurs as a complication of Bacillus anthracis bacteraemic spread in inhalational, gastrointestinal or injectional anthrax.
There is no person-to-person transmission of anthrax.
Treatment
Anthrax is treated with commonly used antibiotics, but it is really important that these are given as soon as possible. If there is a known exposure, giving antibiotics before illness develops (prophylaxis) can prevent severe infection. Cutaneous anthrax is often treated with tablets, but other types of anthrax will need admission to hospital for intravenous antibiotics and other supportive treatment. A combination of antibacterial drugs is usually used. Suitable drugs include amoxicillin, clindamycin, doxycycline and ciprofloxacin.
For anthrax related to intramuscular drug injection, surgical excision of the affected area may be required to achieve source control and prevent fatal systemic disease.
Post-exposure prophylaxis
Post-exposure prophylaxis with antibiotics is recommended for asymptomatic patients with a convincing exposure history.
Vaccination
An anthrax vaccine is available to those in high-risk specialist roles. See information on licensed anthrax vaccines available in the UK.
Testing
Testing for Bacillus anthracis requires isolation of bacteria or spores in a clinical sample of (one of the following):
- blood
- skin lesion swab
- cerebrospinal fluid
- respiratory secretions
Bacillus anthracis will grow on standard agar and appears non-haemolytic on the blood agar plate. Polymerase chain reaction (PCR) testing can be done directly on specimens or on cultured colonies. Mass spectrometry (MALDI TOF) can be used to identify colonies, but laboratories using this method must make sure that they have the correct database that is able to detect biothreat pathogens. Testing is available at the Rare and Imported Pathogens Laboratory (RIPL).
Tests available at the RIPL PCR can be done on suspected culture isolates or directly on samples. Culture may also be used, as well as traditional techniques such as special staining of blood smears on microscope slides. Contact the Imported Fever Service (0844 778 8990) if there are concerns about a suspected case.
Sample type
Discuss with the Imported Fever Service (0844 778 8990). Suspected bacterial isolates should be sent either on a nutrient agar slope or on blood agar.
Biosafety
Bacillus anthracis is an Advisory Committee on Dangerous Pathogens (ACDP) Hazard group 3 organism, and potentially infectious material should be handled in containment level 3 conditions in biosafety class II cabinet. See ACDP guidance.
Environmental hazards
Because spores in the environment may lie dormant for many years, there is a theoretical possibility that spores may be activated and become infective when working in a contaminated environment. This includes building work taking place on agricultural land or certain types of old buildings. See Assessing risk of anthrax on building land on assessing anthrax risk when considering building on potentially contaminated land.
There has been no evidence of anthrax infection following environmental handling or development of brownfield sites, including abattoirs and tanneries. If building work is to take place in areas for which there is documented evidence of a confirmed case of anthrax in livestock, the site can be sampled and specimens sent for analysis for anthrax spores. Further information on environmental sampling for analysis at RIPL can be found at . The environmental request form for these samples can be found at .
Further reading
- Morton N and Swartz MD. Recognition and Management of Anthrax — An Update New England Journal of Medicine 2001: volume 345, pages 1,621-1,626
- US Centres for Disease Control and Protection. Anthrax