Vibrio cholerae (Cholera): Pathophysiology, Diagnosis, and WHO-Recommended Treatment

✅ First-line (WHO / CDC guidelines)

1. Doxycycline (preferred in adults)

• Doxycycline (300 mg), single dose, po

• ✔️ First-line in adults

• ✔️ Reduces duration of diarrhea and bacterial shedding

2. Azithromycin (preferred in children & pregnant women)

• Azithromycin (1 g), single dose, po (adult)

• Children: 20 mg/kg single dose

• ✔️ Safe in pregnancy

• ✔️ Good for areas with tetracycline resistance

3. Ciprofloxacin (alternative)

• Ciprofloxacin (1 g), single dose, po OR

• Ciprofloxacin (500 mg), 1×2 po, for 3 days

• ⚠️ Resistance common in many regions → not always first choice

❌ Not preferred

• Ampicillin / TMP-SMX → high resistance

• Routine antibiotics in mild cases → not always necessary

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⚡ Clinical Pearls (High-Yield for Exam)

• 💧 Most important treatment = ORS or IV fluids

• Antibiotics:

  • ↓ stool volume

  • ↓ duration

  • ↓ transmission

• Severe dehydration → IV Ringer’s lactate FIRST, then antibiotics

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🧠 Easy Mnemonic

“Cholera → DOA”

• Doxycycline

• Oral rehydration

• Azithromycin

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📌 Exam Trap

Even though rehydration is the main treatment: 👉 But in your exam, it will ask you about the antibiotic choice

Answer:

• Adults → Doxycycline (300 mg) single dose po

• Pregnancy / children → Azithromycin (1 g) single dose po

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1. Pathophysiology (How cholera causes disease)

🧬 Organism

• Vibrio cholerae = Gram-negative, comma-shaped, motile bacteria

• Transmitted via the fecal–oral route (contaminated water/food)
  

⚙️ Mechanism of Disease (Core concept you MUST understand)

Step-by-step:

1. Colonization

• Bacteria survive gastric acid → reach the small intestine

• Attach to the intestinal mucosa (non-invasive)

2. Cholera toxin production

• Produces cholera toxin (CTX)

• This is the KEY virulence factor

3. Cellular mechanism (High-yield)

• Toxin activates:👉 Gs protein → ↑ adenylate cyclase → ↑ cAMP

• Result:

  • ↑ Chloride secretion (CFTR channel)

  • ↓ Sodium absorption

  • Water follows electrolytes → massive fluid loss

💧 Clinical effect

• Profuse watery diarrhea (“rice water stool”)

• Rapid dehydration

• Electrolyte imbalance:

  • ↓ K⁺ → muscle weakness

  • ↓ HCO₃⁻ → metabolic acidosis
    

🧠 Easy memory:

👉 “Cholera = cAMP disease → Cl⁻ secretion → Water loss”

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2. Diagnosis

🩺 Clinical diagnosis (MOST IMPORTANT in real life)

• Sudden onset:

  • Profuse watery diarrhea

  • No blood, no pus

• Severe dehydration:

  • Sunken eyes

  • Poor skin turgor

  • Hypotension, tachycardia

👉 In endemic/outbreak setting → clinical diagnosis is enough

🔬 Laboratory diagnosis

1. Stool examination

• Dark-field microscopy → darting motility

• Stool culture:

  • TCBS agar → yellow colonies

2. Rapid tests

• Dipstick antigen tests (used in outbreaks)

3. Labs for severity

• Electrolytes:

  • Hyponatremia / hypokalemia

• ABG:

  • Metabolic acidosis

• Hemoconcentration (↑ hematocrit)

🧠 Exam pearl

👉 Diagnosis is mainly clinical + dehydration assessment👉 Labs confirm but do not delay treatment

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3. Management

⚠️ GOLDEN RULE

👉 Rehydration = life-saving treatment👉 Antibiotics = adjunct

Step 1: Decide OPD vs IPD

OPD (mild–moderate dehydration)

• Oral rehydration solution (ORS)

IPD (severe dehydration)

• Shock, lethargy, unable to drink → ADMIT

Step 2: Rehydration therapy

Severe dehydration (IPD)

• Ringer’s lactate (IV)

  • 30 mL/kg in 30 min

  • then 70 mL/kg in 2.5 hr

Mild–moderate

• ORS

  • 75 mL/kg over 4 hours

Why Ringer’s lactate?

• Contains bicarbonate precursor → corrects metabolic acidosis

Step 3: Antibiotics (Adjunct therapy)

✅ First-line (WHO / CDC)

Adults:

• Doxycycline (300 mg), single dose, po

Pregnancy / Children:

• Azithromycin (1 g), single dose, po

Alternatives:

• Ciprofloxacin (500 mg), 1×2 po, for 3 days

❌ Not recommended:

• Routine antibiotics in mild cases

• Ampicillin / TMP-SMX → resistance

🎯 Why antibiotics?

• ↓ duration of diarrhea

• ↓ stool volume

• ↓ transmission

👉 but NOT life-saving (fluids are!)

Step 4: Electrolyte correction

• Potassium replacement (if hypokalemia)

• Monitor Na⁺, HCO₃⁻

Step 5: Monitoring

• Vital signs

• Urine output

• Hydration status
  

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Complications

• Hypovolemic shock

• Acute kidney injury (AKI)

• Severe metabolic acidosis

• Death (if untreated)

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Exam Summary (Ultra-high yield)

Topic	Key Point
Pathophysiology	↑ cAMP → Cl⁻ secretion → watery diarrhea
Diagnosis	Clinical (rice-water stool + dehydration)
Treatment priority	💧 Fluids FIRST
Antibiotic	Doxycycline (adult), Azithromycin (pregnancy)

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🎯 Final Clinical Pearl

👉 “The patient does NOT die from infection — they die from dehydration.”