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Amoebiasis
Diagnostic Methods
Diagnostic methodsPros and cons
Parasitological diagnosis 
In a case of amoebic dysentery, diagnosis is by microscopic identification of trophozoites or cysts in fresh faecal specimens. A well-trained microscopist is needed because E. histolytica must be differentiated from non-pathogenic amoebae and macrophages. Microscopically the pathogenic amoeba E. histolytica cannot be distinguished from non-pathogenic E. dispar (unless amoebae contain phagocytosed erythrocytes: only E. histolytica is haematophagous!).
In extra-intestinal amoebiasis (suspicion of an amoebic liver abscess), aspirates of abscesses can be investigated.
  • No morphologic differentiation between E. histolytica and E. dispar.
    Microscopy has therefore no diagnostic power to detect asymptomatic carriers infected with E. histolytica!
  • To obtain high sensitivity, multiple stool samples have to be analysed (with three stool samples, sensitivity reaches approx. 95%).
Molecular diagnosis 
Real-time PCR [of rDNA sequence (small subunit) located on an episomal plasmid] allows the discrimination of E. histolytica and E. dispar with a detection limit of one parasite in 10 g stool. It can be execute within 3 hours. This method is the new gold standard for amoebiasis.
  • In contrast to microscopy, allows discrimination between E. histolytica and E. dispar
  • Avoids the over-diagnosis that resulted from poor microscopic quality giving many false positives!
  • Excellent sensitivity (much higher than antigen detection or serology)
  • Excellent specificity
  • Needs expensive equipment and reagents
Antigen detection 
A commercially available test kit differentiates E. histolytica from E. dispar. It detects an E. histolytica-specific adhesion molecule by an enzyme immunoassay.
  • Limitations in sensitivity (compared to real-time PCR)
  • High specificity
Antibody detection 
The detection of circulating antibodies is diagnostically important in invasive amoebiasis (cases of amoebic dysentery or liver abscess). In these cases, very often no cysts or trophozoites can be found in the faeces!
  • Important, high-sensitivity screening method for invasive amoebiasis
  • Not adequate to detect asymptomatic carriers