Conditions · Infectious and tropical diseases
Anthrax !
Anthrax is a bacterial infection caught from spores of infected animals or their products; it can affect the skin, lungs or gut.
Updated 2026-11-01
Structures involved
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Microorganisms that cause it
Why it happens
- Edema and effusions: the four mechanisms
- Adenylyl cyclase
- Cyclic AMP (cAMP)
- Lymph node and spleen under the microscope
What it is
A zoonotic infection by the spore-forming, Gram-positive rod Bacillus anthracis. Depending on how spores enter the body it causes cutaneous, inhalational, gastrointestinal or injection anthrax. It is also a recognised bioterrorism agent.
Who gets it
Mostly a disease of grazing livestock and the people who handle them (farmers, butchers, veterinarians, wool and hide workers). Human cases occur sporadically in parts of Africa, Asia and Latin America, and are rare in Colombia. Cutaneous anthrax makes up the large majority of cases. The 2001 United States letter attacks made inhalational anthrax the model bioterrorism case.
Causes
- Bacillus anthracis, an aerobic, encapsulated, Gram-positive rod that forms very hardy spores in soil
- Spores entering broken skin, inhaled, swallowed in undercooked infected meat or injected with contaminated drugs
- Not transmitted from person to person by the respiratory route
Risk factors
- Handling sick or dead livestock, hides, wool, hair or bone meal
- Eating undercooked meat from animals that died suddenly
- Laboratory work with the organism
- Injecting contaminated drugs
- Deliberate release (bioterrorism)
Pathophysiology
Spores germinate inside macrophages and the bacteria multiply. The antiphagocytic capsule (made of poly-D-glutamate, not polysaccharide) lets them escape killing. Three toxin parts act together: protective antigen carries the others into cells, oedema factor raises cAMP and causes massive swelling, and lethal factor breaks down cell signalling and kills macrophages. In inhalational disease, macrophages carry spores to the mediastinal lymph nodes, where haemorrhagic, necrotising lymphadenitis and mediastinitis develop, followed by bacteraemia, shock and often meningitis.
Classification
- Cutaneous: the most common and least lethal form
- Inhalational: the most lethal form
- Gastrointestinal: oropharyngeal or intestinal
- Injection: deep soft-tissue infection in people who inject drugs
- Systemic complications of any form: sepsis and haemorrhagic meningitis
Symptoms and signs
- Cutaneous: itchy papule that becomes a vesicle, then a painless ulcer with a black eschar and marked surrounding oedema, usually on hands, arms, face or neck
- Regional lymph node swelling with the skin lesion
- Inhalational: flu-like start with fever, sweats, cough and chest discomfort, then sudden breathlessness, hypoxia and shock
- Gastrointestinal: nausea, vomiting (possibly bloody), abdominal pain, bloody diarrhoea and abdominal swelling
- Oropharyngeal form: sore throat, painful swallowing and neck swelling
- Severe headache, confusion or neck stiffness when meningitis develops
Diagnosis
- Clinical
- Suspected from a painless black eschar with oedema in someone exposed to animals or animal products, or from rapidly progressive pneumonia with shock. The case is notified to public health immediately, and the laboratory is warned because the sample may contain a dangerous pathogen.
- Tests
- Gram stain and culture of the skin lesion, blood, pleural fluid, cerebrospinal fluid or sputum (large Gram-positive rods in chains), taken before antibiotics when this does not delay treatment; PCR; detection of lethal factor toxin in blood. Lumbar puncture in systemic disease to look for meningitis.
- Imaging
- Chest X-ray or CT in inhalational disease: widened mediastinum from enlarged haemorrhagic nodes and pleural effusions, often with little pneumonia at first.
Differential diagnosis
- Spider bite or other skin ulcer with necrosis
- Cutaneous leishmaniasis and ecthyma
- Community-acquired pneumonia and severe influenza
- Plague and tularaemia
- Bacterial meningitis from other causes
Goal of treatment
Start effective antibiotics immediately, neutralise toxin in systemic disease, support breathing and circulation, and protect exposed contacts with prophylaxis.
Treatment
- Medical
- Uncomplicated cutaneous anthrax: oral antibiotics (a fluoroquinolone such as ciprofloxacin, or doxycycline). Surgical debridement of the eschar is avoided.
- Acute
- Systemic, inhalational, gastrointestinal or meningeal disease: hospital care with combined intravenous antibiotics (a bactericidal drug plus a protein-synthesis inhibitor), with agents that cross the blood-brain barrier when meningitis cannot be ruled out.
- Acute
- Anthrax antitoxin (monoclonal antibodies or immune globulin) added to antibiotics in severe systemic disease; intensive support for shock.
- Procedure
- Drainage of pleural effusions, mechanical ventilation and airway control when oedema threatens the airway.
- Follow-up
- Standard precautions are enough because person-to-person spread does not occur; contact precautions for draining skin lesions. People exposed to aerosolised spores receive prolonged antibiotic prophylaxis plus vaccine.
Complications
- Sepsis and septic shock
- Haemorrhagic meningitis
- Haemorrhagic mediastinitis and large pleural effusions
- Airway compression from neck oedema
- Intestinal bleeding, perforation and ascites
Prognosis
Treated cutaneous anthrax is almost never fatal, while untreated cases can be fatal in up to about one in five. Inhalational anthrax is almost always fatal without treatment, and even with intensive care about half of patients survive. Meningitis carries a very poor outlook.
Prevention
- Livestock vaccination and safe disposal of animals that die suddenly, without opening the carcass
- Not eating meat from sick or dead animals
- Protective equipment for workers handling animal products
- Vaccine for high-risk workers and, with antibiotics, after aerosol exposure
Test yourself
Think of the answer, then tap the question to see it.
What is the classic lesion of cutaneous anthrax?
A painless ulcer with a black eschar surrounded by marked non-pitting oedema.
What is the typical chest imaging finding in inhalational anthrax?
A widened mediastinum from haemorrhagic mediastinal lymphadenitis, often with pleural effusions.
What is unusual about the capsule of Bacillus anthracis?
It is made of protein (poly-D-glutamate), not polysaccharide.
Which toxin component raises cAMP and causes oedema?
Oedema factor, an adenylate cyclase, carried into cells by protective antigen.
Do patients with inhalational anthrax need airborne isolation?
No. It does not spread person to person; standard precautions apply.
Related conditions
- Community-acquired pneumonia
- Sepsis and septic shock
- Bacterial meningitis
- Cellulitis of the leg
- Necrotizing soft tissue infection (necrotizing fasciitis, gas gangrene)
- Influenza (flu)
Educational information, not medical advice. For any symptom, see a health professional.
Sources: About Anthrax | Anthrax | CDC (Centers for Disease Control and Prevention, 2024); Clinical Overview of Anthrax | Anthrax | CDC (Centers for Disease Control and Prevention, 2024); Anthrax: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2024).
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