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Amoebiasis Diagnosis
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Amoebiasis
Diagnosis

Diagnostic methods

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.

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.

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.

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!

 

Diagnostic strategies

  1. To diagnose a suspicious case of invasive amoebiasis
    For screening, serology is the first choice. In early infection, serology might be negative due to the retarded detection of circulating antibodies. Amoebae can also be detected in abscess aspirates by microscopy or PCR. Stool examinations are often negative in invasive amoebiasis.
     
  2. To detect asymptomatic carriers of E. histolytica
    Screen stool samples with an antigen detection assay or with PCR. Microscopy and serology have no diagnostic value for carriers!
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