Amoebiasis

Clinical data

• The patient was a 46 year old man from a Cape Town township.
• He gave a history of severe diarrhoea and weakness.
• On examination he was dehydrated and shocked.
• He died soon after admission.

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Macroscopic pathology

• The specimen is the caecum and ascending colon, the commonest site for amoebiasis.
• There are multiple mucosal ulcers - these have the classical appearance of amoebic colitis.

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Pathogenesis

• 80% of patients infected with Entamoeba histolytica will be asymptomatic.
• When E. histolytica becomes pathogenic, it invades the crypts of colonic glands and burrows down into the submucosa.
• It  is stopped by the muscularis propria, so then burrows laterally, and with the resulting inflammation and necrosis a flask-shaped ulcer is formed.
• (E. histolytica utilises various virulence factors and enzymes in this process of invasion.) 

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Disease progression

• Initially the mucosa between the ulcers is relatively normal.
• As the ulcers enlarge they become confluent.
• The overlying is mucosa is undermined, and, deprived of its blood supply, it sloughs.
• (This specimen is from a different patient.)

• In about 40% of patients the parasite embolises to the liver via splanchnic vessels.
• In our original patient the result was multiple liver abscesses.
• (Unlike our patient, most patients no longer have gastro-intestinal symptoms when presenting with an amoebic liver abscess.)

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This is the external appearance of the liver. It is enlarged, weighing 3.5kg. One abscess has ruptured through the capsule.

This is the cut surface of the liver.

• There are abscesses varying from 1 to 7cm in diameter.
• They have a shaggy fibrin lining.
• At autopsy the abscesses were filled with a typical reddish-brown liquid "sauce".
• Venous thrombus and a large geographic venous infarct can also be seen.

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Diagnosis

• On microscopy, the stool contained blood, mucus and pus cells.
  • There were also ova of Ascaris lumbricoides and Trichuris trichuria.
  • No Entamoeba histolytica trophozoites or cysts were seen.
     
• Examination of repeated fresh, warm stool samples (x 3) improves the detection rate of active amoeba trophozoites by microscopy.
• If ingested red blood cells are seen within the trophozoite the organism is most likely E. histolytica rather than one of the non-pathogenic amoebae. https://www.cdc.gov/dpdx/amebiasis/index.html#tabs-1247369-2
• E. histolytica can also be diagnosed by specific antigen or serum antibody tests.

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Treatment

• The treatment is metronidazole.
• Drainage of liver abscesses is seldom required.

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