Anthrax: Complete Clinical Chapter on Cutaneous, Inhalational and Gastrointestinal Disease
Clinical Medicine Year 3 • zoonosis, toxin-mediated sepsis and outbreak control
Why anthrax must be recognised early
Anthrax is caused by spore-forming Bacillus anthracis. Most human disease is cutaneous and may begin with a painless itchy papule, but inhalational, gastrointestinal, oropharyngeal and injectional disease can progress rapidly to oedema, bacteraemia, meningitis, shock and death. The patient’s occupation and recent contact with livestock, hides, wool, carcasses or contaminated soil may be more diagnostic than the first physical sign.
Learning outcomes
- Describe the organism, spores, capsule, toxins, reservoirs and routes of exposure.
- Recognise the clinical sequence of cutaneous, inhalational, gastrointestinal/oropharyngeal and injectional anthrax.
- Distinguish anthrax from cellulitis, necrotising fasciitis, plague, tularemia and other eschars.
- Collect specimens safely and understand laboratory confirmation.
- Start urgent antimicrobial, antitoxin, supportive and exposure-management measures.
- Plan vaccination, post-exposure prophylaxis, livestock control and outbreak communication.
1. Causative organism and virulence
B. anthracis is a large, gram-positive, non-motile, non-haemolytic, spore-forming bacillus. Vegetative bacilli multiply in nutrient-rich tissues and produce a poly-D-glutamic acid capsule that inhibits phagocytosis. Spores survive for years in soil, animal products and contaminated equipment.
The tripartite toxin consists of:
- Protective antigen: binds host cells and permits entry of the other toxin components.
- Edema factor: an adenylate-cyclase activity that increases intracellular cAMP and produces marked oedema.
- Lethal factor: disrupts signalling pathways, macrophage function and vascular stability, contributing to shock and death.
2. Reservoir and transmission
Herbivores acquire spores from contaminated soil, pasture, feed or carcasses. Humans are accidental hosts. The supplied teaching deck emphasises contact with cattle, sheep, goats, horses or pigs dying of disease; contaminated hair, wool, hides, drums, brushes, rugs, bone meal and soil; inhalation during hide/wool processing; ingestion of contaminated undercooked meat; and laboratory accidents. Ordinary person-to-person spread is not expected.
| Route | Typical exposure | Resulting form |
|---|---|---|
| Cutaneous inoculation | Handling carcass, hide, wool, meat, soil or infected animal tissue | Cutaneous anthrax |
| Inhalation | Aerosolised spores in tanning, wool, bone processing or laboratory work | Inhalational anthrax |
| Ingestion | Contaminated undercooked meat or animal products | Oropharyngeal or gastrointestinal anthrax |
| Injection | Contaminated injected drugs | Severe injectional soft-tissue/systemic anthrax |
3. Pathogenesis
Spores enter through skin, respiratory or gastrointestinal mucosa. Macrophages transport spores to regional lymph nodes, where germination produces encapsulated bacilli and toxins. Local oedema and necrosis are followed by lymphatic spread, bacteraemia and metastatic seeding. Inhalational disease causes haemorrhagic mediastinitis and pleural effusions; meningeal invasion causes haemorrhagic meningitis. Toxin-driven capillary leak and myocardial/vascular dysfunction lead to shock.
4. Incubation and clinical forms
Incubation is commonly one to seven days, but inhalational spores may remain dormant longer and illness can appear weeks after exposure. Clinical disease has a short prodrome followed by local and systemic manifestations.
4.1 Cutaneous anthrax
Usually begins as an itchy, painless papule on an exposed area. It progresses to vesicle, ulcer/malignant pustule and a depressed black eschar surrounded by non-pitting gelatinous oedema. Fever, malaise, headache, regional lymphadenopathy and lymphangitis may occur. Pain out of proportion, rapidly progressive necrosis or crepitus should raise concern for an alternative or coexisting necrotising infection.
Many localised lesions heal over two to six weeks, but untreated disease can progress to bacteraemia, oedema of the face/neck, respiratory compromise, meningitis and death. Facial lesions are particularly dangerous because oedema can obstruct the airway.
4.2 Inhalational anthrax
The first phase resembles influenza: fever, malaise, myalgia, fatigue, dry cough, chest discomfort, nausea or mild breathlessness. After a short improvement, the patient can abruptly deteriorate with severe dyspnoea, hypoxia, cyanosis, stridor, haemoptysis, shock, confusion, widened mediastinum and pleural effusions. The absence of productive cough does not reassure.
4.3 Oropharyngeal and gastrointestinal anthrax
Oropharyngeal disease produces sore throat, dysphagia, neck oedema, cervical nodes and airway risk. Intestinal disease causes severe abdominal pain, fever, vomiting, bloody diarrhoea, ascites, bowel oedema, ileus, perforation and sepsis. It may be mistaken for surgical abdomen, cholera, dysentery or food poisoning.
4.4 Injectional anthrax
Injection sites may show extensive painful oedema, necrosis, bullae and systemic toxicity without the classic eschar. It progresses rapidly and requires aggressive surgical/infectious-disease assessment.
5. History and examination
5.1 Exposure questions
- Was there a sudden animal death, carcass opening, home slaughter, livestock outbreak or unexplained animal bleeding?
- Did the patient handle hide, wool, hair, bone meal, meat, placenta, carcass or contaminated soil?
- Was meat eaten raw/undercooked, or was a household member exposed?
- Does the patient work in farming, veterinary practice, abattoirs, leather/tanning, wool, laboratories or waste disposal?
- Any injection-drug exposure, travel or previous anthrax vaccination/prophylaxis?
5.2 Examination
Assess airway, breathing and circulation first. Inspect all skin including hidden sites; describe lesion stage, pain, oedema, vesicles, eschar, lymphangitis and regional nodes. Examine oral cavity and neck, chest for hypoxia/pleural signs, abdomen for tenderness/ascites/peritonism, skin/soft tissue, mental state and neurological function.
6. Diagnosis
6.1 Clinical diagnosis
In a compatible exposure, treatment should not wait for confirmation. Anthrax is confirmed by isolation of B. anthracis, detection by validated molecular/immunofluorescence methods or a significant antibody response in an appropriate case. Tell the laboratory in advance because handling cultures can generate dangerous aerosols.
6.2 Specimens
- Unopened vesicle fluid or swab from beneath the lesion edge, not an aggressively scraped eschar.
- Multiple blood cultures before antibiotics if this does not delay life-saving treatment.
- Pleural fluid, CSF, respiratory specimens or tissue only with specialist guidance and safe transport.
- Serum for paired antibody testing in selected cases.
6.3 Imaging and severity tests
Chest radiograph/CT may show widened mediastinum, pleural effusions, hilar adenopathy or infiltrates. Ultrasound/CT evaluates abdominal disease and ascites. FBC, renal/liver profile, coagulation, lactate, glucose, blood gas, ECG and cultures stage sepsis and guide supportive care.
7. Differential diagnosis
| Anthrax presentation | Important differential | Clues favouring the alternative |
|---|---|---|
| Black eschar/oedema | Necrotising fasciitis, ecthyma, spider bite, tularemia, rickettsial eschar, plague | Marked pain, pus, crepitus, rapid spread, purulent nodes, vector/travel history |
| Widened mediastinum/respiratory sepsis | Mediastinitis, pneumonic plague, severe pneumonia, pulmonary haemorrhage | Trauma/procedure, purulent sputum, epidemiology and alternative cultures |
| Abdominal pain/bloody stool | Dysentery, intussusception, appendicitis, bowel perforation, haemorrhagic colitis | Food/water outbreak, surgical signs, stool studies and imaging |
| Injection-site necrosis | Clostridial myonecrosis, necrotising fasciitis, contaminated injection abscess | Gas, severe pain, crepitus, purulence and operative findings |
8. Management
8.1 Immediate actions
- Notify public health and request infectious-disease, critical-care and veterinary coordination.
- Use standard precautions; cover draining lesions and manage contaminated dressings safely. Person-to-person airborne isolation is not usually required.
- Stabilise airway, breathing, circulation and glucose; give oxygen, IV access, careful fluids, vasopressors and organ support as indicated.
- Do not delay antibiotics for specimen collection when systemic anthrax is suspected.
8.2 Antimicrobial and antitoxin principles
Localized uncomplicated cutaneous disease may be treated with a guideline-approved oral agent such as doxycycline or a fluoroquinolone when susceptibility and patient factors permit. Systemic, inhalational, gastrointestinal, injectional or meningeal disease requires urgent IV combination therapy according to current national/WHO guidance, often including a fluoroquinolone plus a protein-synthesis inhibitor. Add anthrax antitoxin for systemic toxin-mediated disease where available. Historical penicillin-only teaching regimens should not be copied into modern severe disease without susceptibility and specialist review.
Localized cutaneous disease
Appropriate oral therapy, wound cover, oedema/airway assessment and follow-up. Avoid routine incision or debridement of the eschar.
Systemic/inhalational/GI disease
IV combination therapy, antitoxin, sepsis resuscitation, respiratory support, pleural assessment and high-dependency monitoring. Search for meningitis and bowel perforation.
Meningitis
Use CNS-penetrating combination therapy plus antitoxin and urgent neurological/critical-care support; manage cerebral oedema and seizures.
Injectional disease
Broad specialist-guided therapy, sepsis care and early surgical review for necrosis, compartment syndrome or abscess. Obtain cultures before debridement if safe.
8.3 Airway and surgical care
Facial/neck oedema, stridor or oropharyngeal disease can make intubation difficult; involve anaesthesia early. Drain pleural collections when indicated. Surgery is reserved for perforation, uncontrolled necrosis, compartment syndrome or source control—not routine excision of uncomplicated cutaneous eschars.
9. Complications
- Toxin-mediated shock, capillary leak, acute respiratory distress and multi-organ failure.
- Haemorrhagic mediastinitis, pleural effusion, empyema and respiratory failure.
- Haemorrhagic meningitis, cerebral oedema, seizures and focal deficits.
- Gastrointestinal bleeding, ileus, perforation and peritonitis.
- Massive facial/neck oedema and airway obstruction.
- Renal injury, DIC, myocardial dysfunction and death.
10. Post-exposure management and prevention
10.1 Contacts and exposed workers
Identify people who handled the animal, carcass, hides, wool, meat, contaminated soil or laboratory material. Assess symptoms, exposure intensity and vaccination status. Give guideline-based post-exposure prophylaxis and vaccine when indicated, and arrange prolonged symptom surveillance because spore germination can be delayed.
10.2 Livestock and environmental control
- Do not open or butcher animals suspected of anthrax; involve veterinary officers.
- Dispose of carcasses and contaminated materials by approved procedures; avoid spreading spores through uncontrolled burial or transport.
- Vaccinate livestock in endemic areas and investigate sudden animal deaths.
- Educate farmers, herders, abattoir workers, leather/wool workers, hunters and consumers.
- Decontaminate equipment, clothing and workspaces under public-health guidance.
11. Clinical reasoning examples
Example A: painless black lesion
A butcher develops an itchy papule on the hand that becomes a painless black eschar with marked oedema. Ask about carcass/hide exposure, cover the lesion, notify public health, collect a safe specimen and begin guideline-based therapy; do not incise it as ordinary cellulitis.
Example B: respiratory deterioration after wool exposure
A worker has a flu-like illness followed by sudden dyspnoea, hypoxia and widened mediastinum. Treat as inhalational anthrax until excluded: resuscitate, collect blood cultures, notify public health, start IV combination therapy and seek antitoxin/critical care.
Example C: abdominal anthrax in an outbreak
Several people develop severe abdominal pain and bloody diarrhoea after eating meat from a sudden animal death. Manage sepsis and surgical complications while coordinating outbreak investigation, food control and veterinary response.
12. Examination pearls
- A painless black eschar with gelatinous oedema is more suggestive of anthrax than ordinary cellulitis.
- Inhalational anthrax may worsen abruptly after a mild prodrome.
- Person-to-person spread is not the usual route; contaminated animal products and soil are the public-health focus.
- Notify, collect safely and treat empirically—waiting for a perfect result can be fatal.
- Antitoxin and critical-care support matter in systemic toxin-mediated disease.
13. References
- SlideShare: Anthrax — organism, transmission, clinical forms, diagnosis, management and prevention.
- WHO/CDC anthrax clinical, laboratory and public-health guidance.
- Uganda Clinical Guidelines and district veterinary outbreak protocols.
