10.02 Cholera

Overview & Causative Agent

• Cholera is a severe, acute diarrheal disease caused by the bacterium Vibrio cholerae.
• It remains a significant public health challenge in regions with inadequate water treatment, poor sanitation, and limited hygiene.

Bacterium Characteristics

• Causative Agent: Vibrio cholerae
• Morphology:
  • Shape: Comma-shaped, Gram-negative rod
  • Motility: Possesses a single polar flagellum enabling motility
• Identification:
  • Visible under an electron microscope at ×13,400 magnification
  • Exhibits characteristic agglutination with specific antisera

Transmission of Cholera

Mode of Transmission

• Water-borne: Contaminated drinking water sources
• Food-borne: Consumption of contaminated food items

High-Risk Areas

• Geographical Distribution: Predominantly in parts of Asia, Africa, and Latin America
• Risk Factors:
  • Lack of access to clean water
  • Inadequate sanitation facilities
  • Poor hygiene practices

Transmission Pathways

1. Contaminated Water Supplies:
   • Source: Infected individuals excrete V. cholerae in feces
   • Mechanism: Contamination of communal water sources through sewage runoff
2. Contaminated Food Handling:
   • Process: Food prepared or handled by infected individuals without proper hygiene
   • Examples: Raw seafood, street-vended foods
3. Use of Contaminated Utensils:
   • Transmission: Sharing utensils washed in contaminated water

Infection Process

Survival in the Stomach

• Acid Resistance: V. cholerae is susceptible to low pH; stomach acid (pH < 4.5) can kill the bacteria
• Survival Strategy: Bacteria that survive gastric acid reach the small intestine

Path to the Small Intestine

• Colonization: V. cholerae adheres to the mucosal lining of the small intestine
• Proliferation: Bacteria multiply rapidly in the alkaline environment of the small intestine

Toxin Production

• Choleragen (Toxin):
  • Type: Enterotoxin composed of A and B subunits
  • Mechanism:
    • A Subunit: Activates adenylate cyclase, increasing cAMP levels
    • Effect: Disrupts ion transport, leading to chloride and bicarbonate secretion into the intestinal lumen
• Physiological Impact:
  • Water and Electrolyte Loss: Rapid efflux of salts and water results in severe, watery diarrhea (“rice-water” stools)

Symptoms

• Primary Symptoms:
  • Profuse, watery diarrhea
  • Vomiting
  • Rapid dehydration
  • Electrolyte imbalance
• Severe Consequences:
  • Shock
  • Renal failure
  • Death within 24 hours if untreated

Clinical Information

Treatment of Cholera

Oral Rehydration Therapy (ORT)

• Composition: Solution containing salts (sodium, potassium) and glucose
• Administration:
  • Mild to Moderate Cases: Oral intake of ORT
  • Severe Cases: Intravenous (IV) rehydration
• Mechanism:
  • Glucose Facilitation: Enhances sodium and potassium ion uptake via co-transport mechanisms
  • Electrolyte Balance: Restores osmotic balance in blood and tissues

Antibiotic Therapy

• Usage: May be administered in severe cases to reduce the duration of diarrhea and bacterial shedding

Supportive Care

• Monitoring: Vital signs, electrolyte levels
• Nutritional Support: Gradual reintroduction of normal diet

Prevention of Cholera

Challenges in Developing Regions

• Urbanization: Rapid growth without adequate sewage and clean water infrastructure
• Sanitation: Poor waste management facilitates contamination of water sources

High-Risk Practices

• Irrigation with Raw Sewage: Spreads V. cholerae to crops
• Insufficient Cooking: Consuming undercooked or raw foods increases risk
• Water Contamination: Using contaminated water for drinking, cooking, or washing

Prevention in Developed Countries

• Clean Water Supply:
  • Sewage Treatment: Effective sewage management reduces environmental contamination
  • Chlorinated Piped Water: Kills V. cholerae, breaking the transmission cycle
• Food Safety Regulations:
  • Ensuring proper handling and cooking of food to eliminate pathogens

Impact of Disasters

• Natural Disasters: Earthquakes, hurricanes, floods disrupt infrastructure
• Consequences:
  • Inadequate sanitation
  • Contaminated water supplies
  • Overcrowded shelters

Vaccination

• Oral Cholera Vaccine:
  • Availability: Approved in the USA since 2016
  • Usage:
    • Travelers to endemic regions
    • Mass vaccination campaigns in outbreak areas

Frequently Asked Questions

How is cholera transmitted from person to person?

Answer: Cholera spreads primarily through ingestion of water or food contaminated with Vibrio cholerae. In regions with poor sanitation, bacteria from the feces of infected individuals contaminate water supplies or are directly transmitted through improper food handling.

Infection Potential Calculation

Scenario: One person excretes 10¹³ cholera bacteria daily; the infective dose is 10⁶.

Calculation:

Interpretation: One infected person can potentially infect up to 10 million people in one day.

Why is cholera risk high following natural disasters?

Answer: Natural disasters damage water and sanitation infrastructure, leading to inadequate sewage disposal and contaminated water sources. Overcrowded conditions and disrupted services create an environment conducive to the rapid spread of cholera.

Precautions for Visitors to Cholera-Endemic Areas

Recommendations:

1. Water Safety:
   • Drink only bottled or boiled water
   • Use water purification tablets if necessary
2. Food Safety:
   • Avoid raw or undercooked foods
   • Steer clear of food from street vendors
3. Hygiene Practices:
   • Wash hands frequently with soap
   • Use hand sanitizer when soap is unavailable
4. Vaccination:
   • Consider oral cholera vaccine for added protection if available

Figure

• Description: This figure depicts the administration of IV rehydration therapy to children affected by cholera, highlighting the severe impact of the disease in war-torn or disaster-affected regions where sanitation and clean water access are compromised.

Note: Effective management of cholera relies on a combination of prompt medical treatment, improved sanitation, clean water supply, public health education, and vaccination strategies to prevent outbreaks and reduce mortality rates.