Bacillus anthracis: Pathogenesis, Pathology, Clinical Findings, Diagnostic Laboratory Tests, Resistance and Immunity, Treatment, Epidemiology, Prevention, and Control.

Question 1

Bacillus anthracis - Overview

Answer 1

1. 🦠 Bacillus anthracis is a large, Gram-positive, spore-forming bacillus.
2. It is aerobic or facultative anaerobic and forms highly resistant spores in the presence of oxygen.
3. It has a unique capsule made of poly-D-glutamate, which is antiphagocytic.

Question 2

Bacillus anthracis - Virulence factors

Answer 2

⚙️ Virulence Factors:
1. Capsule – poly-D-glutamate; antiphagocytic
2. Exotoxins (Anthrax Toxin):
 🔹 Protective Antigen (PA): Binds host cells, forms a channel
 🔹 Edema Factor (EF): ↑ cAMP → edema
 🔹 Lethal Factor (LF): Zinc protease → kills macrophages
🔬 Genes for toxins and capsule are carried on plasmids pXO1 and pXO2.

Question 3

Bacillus anthracis - Pathogenesis

Answer 3

✅ Pathogenesis: Spores enter the body via skin, lungs, or GI tract. Inside the host, spores germinate, bacteria multiply, and release anthrax toxin (PA + EF/LF) → systemic disease with necrosis, edema, and sepsis.

Question 4

Bacillus anthracis - Pathology

Answer 4

🧬 Pathology:
- Spores germinate at entry site → bacteria multiply locally
- Toxins spread → hemorrhagic lymphadenitis, edema, necrosis
- May lead to sepsis, hemorrhagic meningitis, and death

Question 5

Bacillus anthracis - Clinical forms

Answer 5

🏥 Clinical Forms:
1. Cutaneous Anthrax: Painless papule → vesicle → black eschar with edema
2. Inhalation Anthrax (Woolsorter’s Disease): Cough, fever → hemorrhagic mediastinitis, shock
3. Gastrointestinal Anthrax: Ingested spores → ulcers, bloody diarrhea, sepsis
4. Injectional Anthrax: Seen in drug users → deep soft tissue infection, severe sepsis

Question 6

Bacillus anthracis - Diagnostic laboratory tests

Answer 6

🧪 Lab Tests:
- Gram stain: Gram-positive, ‘boxcar’ bacilli in chains
- Culture: Non-hemolytic, ‘medusa head’ colonies on blood agar
- PCR/ELISA: Detect toxin genes/proteins
- Chest X-ray (inhalation): Widened mediastinum
- Serology: Detect anti-PA antibodies
- Immunohistochemistry: Detects B. anthracis in tissues

Question 7

Bacillus anthracis - Resistance and immunity

Answer 7

🧱 Resistance & Immunity:
- Spores = highly resistant to heat, drying, disinfectants
- Capsule = resists phagocytosis
- Recovery → protective immunity via anti-PA antibodies
- Vaccines use protective antigen (PA) to induce immunity

Question 8

Bacillus anthracis - Treatment

Answer 8

💊 Treatment:
- Cutaneous (mild): Oral ciprofloxacin or doxycycline x 7–10 days
- Systemic Anthrax: IV ciprofloxacin + 1–2 additional antibiotics (e.g., clindamycin, meropenem) + antitoxins (raxibacumab or obiltoxaximab)
- Post-exposure prophylaxis: 60 days of antibiotics + 3 doses of anthrax vaccine

Question 9

Bacillus anthracis - Epidemiology

Answer 9

🌍 Epidemiology:
- Natural reservoir: soil (spores survive decades)
- Affects herbivores (cattle, sheep); humans via contact/inhalation
- Not spread person-to-person
- Bioterrorism agent (Category A); used in 2001 U.S. mail attacks

Question 10

Bacillus anthracis - Prevention and control

Answer 10

🛡️ Prevention & Control:
- Human vaccine (BioThrax): For high-risk individuals
- Animal vaccination in endemic areas
- Post-exposure prophylaxis: Vaccine + 60 days of antibiotics
- Control carcasses, decontaminate areas, wear PPE
- Bioterrorism readiness: Stockpiles of vaccine and antitoxins

Question 11

Mnemonic - Anthrax toxin

Answer 11

🧠 Mnemonic:
- PA + EF = Edema
- PA + LF = Lethal