Things I’m learning at med school: Cholera
Vibrio cholerae; bacteria
Comma shaped bacillus (i.e. vibrios)
Causes acute intestinal infection
Usually has a 24-48 hour incubation period
Primarily transmitted through the faecal-oral route
Occurs mainly in Africa due to poor sanitation
Most bacteria do not survive the stomach acid (therefore a vast exposure is required for infection to occur).
Those that do survive the acid shut down protein production to conserve energy until they reach the small intestine. Here they will each grow a flagellum to propel them through the thick mucosal wall where they may thrive (held in position by pili).
The bacteria then produce an enterotoxin (a protein toxin released by a microorganism in the intestine). This binds to the surface of intestinal epithelial cells and is taken into the cell via receptor-mediated endocytosis.
To put it simply, it is metabolised within the cell, leading to increased cAMP concentration, which massively activates cytosolic PKA (protein kinase A). These active PKA then open up the cystic fibrosis transmembrane conductance regulator (CFTR) proteins, which leads to Ca2+ being pumped out into the intestinal lumen, which in turn leads to secretion of H2O, Na+, K+, and HCO3-.
In addition, The entry of Na+ and consequently the entry of water into enterocytes are diminished. The combined effects result in rapid fluid loss from the intestine, up to 2 liters per hour, leading to severe dehydration.
There are few symptoms specific to cholera, aside from a rapid onset of severe diarrhoea, abdominal cramping, a rice-water stool and often metabolic acidosis (due to the secretion of HCO3-), which can also lead to vomiting.
All other signs/symptoms are that of dehydration:
Dry mucous membranes
Lack of tears
Low urine output
Delayed capillary refill
Treating cholera is incredibly simple, only requiring rehydration of water and electrolytes
Oral rehydration therapy (ORT) - This is the easiest treatment for cholera and is perfectly suitable for water rehydration however it does not provide any electrolytes. This is a mixture of water, glucose and salt (adding a mashed banana will provide potassium) - it is similar to normal saline but with glucose to increase water absorption.
IV Lactated Ringer’s solution (or Hartmann’s solution) - This is similar to ORT but it will also provide the required electrolytes and correct metabolic acidosis. The components of this are: sodium, potassium, chloride, calcium and lactate.
Antibacterials (such as tetracycline) can be administered in the treatment of cholera however they are not necessary for a recovery; they reduce the duration of the disease and improve symptoms.