Anthrax: Causes, Pathogenesis, and Clinical Forms

Causative Agent

Bacillus anthracis – a Gram-positive, rod-shaped, spore-forming bacterium.

Geographic Distribution

Worldwide.

Pathogenesis

Spores are highly resistant and can survive decades in soil. When inhaled, they are phagocytosed by alveolar macrophages, germinate into vegetative forms, multiply, and produce toxins that cause tissue destruction and edema.

• Lethal toxin: Inhibits protein synthesis.
• Edema toxin: Increases capillary permeability.

Clinical Forms

Cutaneous Anthrax (Most Common)

Occurs on exposed skin (face, neck, forearms, hands). A painless papule progresses to a black necrotic eschar with regional lymphadenopathy. Low mortality with early treatment.

Pulmonary (Inhalational) Anthrax

Presents like community-acquired pneumonia (fever, chills, myalgias, cough, dyspnea). Mediastinal widening on chest X-ray. Rapid deterioration and septic shock; high mortality.

Gastrointestinal Anthrax

From ingestion of contaminated meat. Nausea, vomiting, abdominal pain, diarrhea; toxemia and shock possible. Rare but high mortality.

Meningeal Anthrax

Rare; spores reach CNS. Headache, stiff neck, nausea, vomiting, confusion, seizures. High mortality if untreated.

Diagnosis

Based on clinical findings, lab tests, and epidemiology. Tests include Gram stain/culture, PCR for B. anthracis DNA, and serology for antibodies.

Treatment

Early antibiotics: penicillin, doxycycline, ciprofloxacin, or vancomycin.

Prevention

• Vaccination for high-risk groups (military, lab workers, veterinarians).
• Personal protective equipment when handling potentially contaminated materials.
• Environmental control: proper carcass disposal and decontamination.

Epidemiology

Primarily an animal disease; humans infected via contact with infected animals/products (wool, hides, meat), inhalation of spores, or ingestion of contaminated food/water.