Makindo Medical Notes.com

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

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 with gram-negative bacillus Vibrio cholera
• Epidemics once seen throughout Western world
• Now isolated to areas of overcrowding and poor sanitation
• Pathogenicity due to release of cholera toxin

Epidemiology

• Current pandemic is caused by V. cholerae O1 El Tor organisms
• Seen in South Asia, sub-Saharan Africa, and Haiti
• Affects man only with no animal hosts
• Spread by infected faeces entering the water source or direct Faeco-oral spread

Historical

• John Snow and the London epidemic isolated to a water pump in 1854
• Robert Koch identified organism in Kolkata in 1884

Aetiology

• non Invasive organism - fever is rare
• Cholera toxin activates intestinal cells adenylate cyclase
• Generation of cyclic Adenosine monophosphate (cAMP).
• Cholera opens chloride channels, letting chloride and water leave cells
• Cholera toxin is composed of one A subunit and five B subunits
• Toxin subunit B adheres to intestinal surface receptor GM1 ganglioside receptors
• Toxin subunit A stimulates adenylate cyclase and increases cAMP causing increased chloride loss and reduced-sodium uptake
• There is torrential loss of isotonic fluid 'rice water' leads to profound dehydration

Characteristics

• Comma shaped bacillus with a single polar flagellum
• Found in saltwater. Facultative anaerobes
• Oxidase positive (unlike Enterobacteriaceae) and grows in alkaline conditions
• Divided by their "O" types: O1 is the main cause of cholera
• O139 strains of El Tor biotype cause cholera
• non 01 strains may occasionally cause a less severe diarrhoea
• Over 200 serotypes based on O antigen

Clinical

• Sudden onset fishy-smelling rice water stools
• Associated with dehydration, hypovolaemia and shock
• Vomiting and abdominal pain is mild
• Death in up to 50% of untreated patients
• non 01 strains may occasionally cause a less severe diarrhoea

Investigations

• Gram stain of stools may show curved gram-negative rods
• Alkaline broth used to grow organisms selectively from faeces
• Stool cultures with pH > 8 with a elective media

Management

• Issues are massive Diarrhoeal fluid loss, hypotension, death
• Support with Oral Rehydration therapy or Intravenous fluids
• ORT - Mixture of water + salt + glucose which uses a separate Na/Glucose uptake mechanism
• Azithromycin or Doxycycline single dose

Prevention

• Surveillance, case detection, fluid resuscitation and management, vaccination, and provision of safe water and adequate sanitation.
• There are 2 oral killed cholera vaccines that are currently commercially available and approved by the World Health Organization