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Chapter 4: Gastrointestinal infections 153

Investigations
The toxin is demonstrable in the faeces.
Enterocyte
Management Raised cAMP
Treatmentissupportivewithrespiratorysupportasindi-
cated. Intravenous antitoxin and guanidine hydrochlo-
ride to reverse neuromuscular blockade has been used. G M1 ganglioside

Cholera toxin
Cholera
LUMEN Secretion of fluid
Definition
Cholera is an acute infection of the gastrointestinal tract Figure 4.2 Pathophysiology of secretory diarrhoea in cholera.
caused by the Gram-negative bacterium Vibrio cholera.
3 The B subunit of the exotoxin binds to intestinal ep-
Incidence itheliumexpressingtheG M1 gangliosideandtheAunit
66 cases in the past 20 years in the United Kingdom, activates adenylate cyclase (see Fig. 4.2). The result is
endemic in South East Asia and South America. an increase in cellular levels of cAMP and massive se-
cretion of isotonic fluid into the intestinal lumen.
Aetiology
4 Asecondtoxin termed zonula occludens toxin (ZOT)
V. cholera is found free living in fresh water, it is only
damages the tight junctions between enterocytes al-
pathogenic in humans. It can contaminate shellfish.
lowing the passage of water and electrolytes.
Transfer from human carriers is via the faeco–oral route.
The serovar 0:1 is the major pathogenic strain and Clinical features
is divided into two biotypes; classical and the more Theincubationperiodisbetweenafewhoursand1week.
widespread El Tor (named after the quarantine camp Most patients have a mild self-limiting diarrhoeal illness
in which it was discovered). Phage typing can be used to but in severe cases there may be watery diarrhoea with
examine epidemics to try and see if the observed condi- mucous, termed rice water stool. It is vital to adequately
tions originated from a single source (see Fig. 4.1). fluid resuscitate patients with such diarrhoea to prevent
the onset of hypovolaemic shock.
Pathophysiology
1 V. cholera is damaged by stomach acid therefore pa- Investigations
tients on acid suppressing medication are particularly The diagnosis is often made on clinical features alone,
susceptible to infection. pendingtheresultsofstoolcultureswhicharediagnostic.
2 Once in the small bowel proliferation occurs and there However, stool microscopy may reveal the characteristic
is production of an exotoxin. motile organisms.

Serotyping of Biotype: growth on
Bacteria somatic O media, and enzyme
antigens production

Classical
Serovar 0:1

Vibrio cholera El Tor
Non 0:1
Figure 4.1 Subtypes of cholera.