Diarrhoeal disease

Abstract

489 CME Tropical medicineestuarine waters of the Ganges delta acquired a cassette of virulence genes on one or more plasmids and evolved into a major human pathogen which has unleashed seven pandemics and spread to all continents. 7,8 Its power to kill spectacularly in a matter of hours has inspired considerable fear, and even novels! The pathophysiology is still not completely understood (in particular, the interaction between toxins and the enteric nervous system), but several points can be made (Fig 1 illustrates the physiology of cholera):1 The mucosal architecture of the small intestine, in particular the epithelium, remains intact. 2 Large numbers of bacteria are required to induce disease. Each bacterium liberates a finite quantity of cholera toxin which induces irreversible changes in a number of epithelial cells. The consequence is that the infectious dose is high -about 10 9 bacteria are required to produce clinical cholera in a healthy person. 9 3 The greater the amount of toxin synthesised in the gut, the greater the severity of clinical illness. The toxin induces cyclic adenosine monophosphate synthesis in the cell, leading to changes in the balance of water and salt transport so that the small intestine becomes a net secretor of water and electrolytes. This overwhelms the reserve absorptive capacity of the colon and unabsorbed water reaches the rectum. 4 When a cell is exposed to cholera toxin, although it is morphologically normal, its chloride secretion is irreversibly turned on. This does not prevent the cell from absorbing sodium (Na) through the Na-glucose co-transporter. By providing extra substrate for the Na-glucose cotransporter, the re-uptake of Na (then water) becomes possible. 5 The faecal losses of electrolytes are relatively constant, so cholera leads fairly predictably to a hypokalaemic metabolic acidosis in addition to severe volume depletion. 6 Once the toxin is removed, normal epithelial regeneration replaces the population of cells which have been physiologically reprogrammed with a new population of enterocytes which secrete water and electrolytes normally.Management. The management of cholera exploits these principles:1 Oral rehydration solution (ORS) is used to stimulate Na-glucose cotransport and increase uptake of water and electrolytes into the small intestine. The ORS must contain potassium, and ideally bicarbonate CME Tropical medicineor citrate to help compensate for the loss of bicarbonate in stool. 2 Antibiotics are useful to reduce both the amount of toxin being generated and stool losses, and to allow the repopulation of the epithelial compartment with normal cells, thus shortening the clinical illness.The International Centre for Diarrhoeal Disease Research in Bangladesh has extensive experience of managing cholera. Using the guiding principles listed above, it has managed to reduce the mortality of cholera to well below 1%. The addition of zinc has allowed a further reduction in duration of illness. 3,10,11 Oral rehydration therapy is the mainstay of treatment, wi...

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