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Chapter 4: Gastrointestinal infections 151

Identification of the C. difficile toxin in the stool by Amoebiasis

ELISA is specific and is routinely used.
Definition
Culture is possible but usually not required.

Adiarrhoealillnessordysenterycausedbyinfectionwith
amoebae.
Management
The broad-spectrum antibiotics should be stopped and
acombination of adequate fluid replacement and oral Prevalence
metronidazole is used. Second-line therapy is with oral Up to 50% of the population in the tropics.
vancomycin.
Geography
Giardiasis Occurs worldwide but most common in the tropics and
subtropics.
Definition
Infection of the gastrointestinal tract by Giardia lamblia
a flagellate protozoa. Aetiology
The condition is caused by Entamoeba histolytica,trans-
Aetiology mission occurs through food and drink contamination
Giardia is found worldwide especially in the tropics and or by anal sexual activity.
is an important cause of traveller’s diarrhoea, it is also
found in the United Kingdom. Pathophysiology
The amoeba can exist as two forms; a cyst and a tropho-
Pathophysiology zoite, only the cysts survive outside the body. Following
The organism is excreted in the faeces of infected pa- ingestion the trophozoites emerge in the small intestine
tients as cysts. These are ingested, usually in contami- and then pass to the colon where they may invade the
nated drinking water. The organism then develops into a epithelium causing ulceration.
trophozoite, which colonises and multiplies in the small
intestine. Diarrhoea results from inflammation of the
Clinical features
epithelium.
Asymptomatic carriage and excretion of potentially

infective cysts.
Clinical features
Patients may have a gradual onset of mild intermittent
Patients may be asymptomatic carriers or may present
diarrhoea and abdominal discomfort. Subsequently
1–2weeksafteringestion ofcystswithdiarrhoea,nausea,
bloody diarrhoea with mucus and systemic upset may
anorexia, abdominal discomfort and distension. There
occur as a result of colitis, which may be severe. A
may be steatorrhoea, and if the condition is prolonged
fulminating colitis with a low-grade fever and dehy-
there may be weight loss.
dration may develop.
Investigations
Stoolspecimen:Identificationoftrophozoitesorcysts. Complications

Aspirates from the duodenum or jejunal biopsy can Severe haemorrhage may result from erosion into a

be used for identification. blood vessel. Amoebae may then pass to the liver caus-
Serological responses can be measured. ing hepatitis and intrahepatic abscesses.

Amoebic liver abscesses result in tender hepatosplen-

Management omegaly, a swinging fever and malaise.
A 3-day course of metronidazole or a single oral dose of Progression of fulminant colitis to toxic dilatation
tinidazole are highly effective treatments for giardiasis. risks perforation and peritonitis.
Prevention is by improved sanitation and precautions Chronic infection causes fibrosis and stricture forma-
with drinking water. tion.