Makindo Medical Notes

Related Subjects: |Cholera (Vibrio cholera) |Circulatory Shock (Volume loss) |Gastroenteritis |Diarrhoea |Notifiable disease and organisms UK

Cholera (Vibrio cholerae) is a lethal cause of dehydrating diarrhoea, either waterborne or from contaminated food. A person with cystic fibrosis cannot contract cholera because the toxin cannot open the chloride channels in the small intestine.

About

• Notifiable infection caused by the gram-negative bacillus Vibrio cholerae.
• Once caused epidemics throughout the Western world.
• Now largely isolated to areas with overcrowding and poor sanitation.
• Pathogenicity is due to the release of cholera toxin, leading to massive fluid loss.

Epidemiology

• The current pandemic is caused by V. cholerae O1 El Tor organisms.
• Predominantly seen in South Asia, sub-Saharan Africa, and Haiti.
• Affects only humans, with no animal hosts.
• Spread via infected feces contaminating water sources or direct fecal-oral transmission.

Historical

• John Snow linked the London cholera epidemic in 1854 to a contaminated water pump.
• Robert Koch identified the cholera organism in Kolkata in 1884.

Aetiology

• Non-invasive organism: Fever is rare.
• Cholera toxin: Activates adenylate cyclase in intestinal cells, leading to increased cyclic AMP (cAMP) levels.
• Cholera toxin causes the opening of chloride channels, leading to chloride and water loss from cells.
• Toxin structure: Composed of one A subunit and five B subunits. The B subunits bind to the GM1 ganglioside receptors on the intestinal surface, while the A subunit activates adenylate cyclase, increasing cAMP and promoting chloride loss and reduced sodium uptake.
• Rice-water stools: Torrential loss of isotonic fluid results in the characteristic "rice water" stools, leading to severe dehydration.

Characteristics

• Comma-shaped bacillus: With a single polar flagellum for motility.
• Found in saltwater environments. Facultative anaerobes.
• Oxidase positive: Unlike Enterobacteriaceae, Vibrio cholerae grows in alkaline conditions.
• Divided by "O" antigen types: O1 is the main cause of cholera.
• O139 strains: El Tor biotype also causes cholera outbreaks.
• Non-O1 strains may cause less severe diarrhoea occasionally.
• Over 200 serotypes based on the O antigen.

Clinical Features

• Sudden onset of rice-water stools: Often with a fishy odor.
• Associated with severe dehydration, hypovolemia, and shock.
• Vomiting and abdominal pain are mild in most cases.
• Mortality rate is up to 50% in untreated cases.
• Non-O1 strains may occasionally cause less severe diarrhoea.

Investigations

• Gram stain: Shows curved, gram-negative rods in stool samples.
• Alkaline broth culture: Used to selectively grow organisms from feces.
• Stool cultures: Performed in a medium with pH > 8 to isolate Vibrio cholerae.

Management

• Primary concerns: Massive diarrhoea, fluid loss, hypotension, and potential death.
• Oral rehydration therapy (ORT): Mixture of water, salt, and glucose to enhance sodium and water absorption via the Na/Glucose uptake mechanism.
• Intravenous fluids: Used for severe dehydration.
• Antibiotics: Single-dose azithromycin or doxycycline may be given to reduce the severity and duration of symptoms.

Prevention

• Focus on surveillance, case detection, fluid resuscitation, vaccination, and provision of safe water and adequate sanitation.
• Two oral killed cholera vaccines are currently commercially available and approved by the World Health Organization (WHO).