Amoebiasis - Gastrointestinal infections

Amoebiasis

Definition

A diarrhoeal illness or dysentery caused by infection with amoebae.

Prevalence

Up to 50% of the population in the tropics.

Geography

Occurs worldwide but most common in the tropics and subtropics.

Aetiology

The condition is caused by Entamoeba histolytica, transmission occurs through food and drink contamination or by anal sexual activity.

Pathophysiology

The amoeba can exist as two forms; a cyst and a trophozoite, only the cysts survive outside the body. Following ingestion the trophozoites emerge in the small intestine and then pass to the colon where they may invade the epithelium causing ulceration.

Clinical features

Asymptomatic carriage and excretion of potentially infective cysts.

Patients may have a gradual onset of mild intermittent diarrhoea and abdominal discomfort. Subsequently bloody diarrhoea with mucus and systemic upset may occur as a result of colitis, which may be severe. A fulminating colitis with a low-grade fever and dehydration may develop.

Complications

Severe haemorrhage may result from erosion into a blood vessel. Amoebae may then pass to the liver causing hepatitis and intrahepatic abscesses.

Amoebic liver abscesses result in tender hepatosplenomegaly, a swinging fever and malaise.

Progression of fulminant colitis to toxic dilatation risks perforation and peritonitis.

Chronic infection causes fibrosis and stricture formation.

Investigations

Serodiagnosis is by fluorescent antibody titre, positivity is low in asymptomatic carriers. Stool examination may reveal the trophozoites. Liver disease should be suspected if alkaline phosphatase rises, hepatic ultrasound is used to confirm the diagnosis.

Management

Metronidazole is the drug of choice, large liver abscesses require ultrasound guided percutaneous drainage. Prevention is difficult due to the high prevalence of asymptomatic carriers, boiling water for 10 minutes kills the cysts.