Culture of amoebae

Culture of amoebae has been long established (Robinson 1968). However, it is carried out in few laboratories and usually as part of isoenzyme typing of E. histolytica isolates. Nevertheless, Haque et al. (1995) found that culture in Robinson's medium (1968) was more reliable than microscopy in identifying Entamoeba species.

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Triage Micro Parasite Panel (Biosite Inc., San Diego, CA) is a commercial kit detecting antigens of G. intestinalis, E. histolytica/dispar and Cryptosporidium in unpreserved, fresh or frozen stool samples. The test is rapid and can be used as a screen for immediate testing of specimens however, the high cost of the assay may limit its applications and this test does not differentiate between E. histolytica and E. dispar (Sharp et al. 2001).

Differentiation of Entamoeba histolytica and Entamoeba dispar

Entamoeba histolytica and the non-pathogenic E. dispar are morphologically identical. The finding of haematophagous trophozoites is diagnostic for E. histolytica. Otherwise positive findings, whether of cyst or trophozoite must be reported as E. histolytica/E. dispar. Antigen-detection methods that can differentiate between E. histolytica and E. dispar have been developed recently (Abd-Alla et al. 1993; Haque et al. 1994) and a commercial version of one of these, the E. histolytica test (TechLab, Inc., Blacksberg, VA) has been tested in the field with encouraging results (Haque et al. 1995). An improved, second-generation LabTech kit showed an increased sensitivity of 100% and 95.7% of antigen detection in intestinal infections and liver abscess cases respectively (Haque et al. 2000). Another ELISA-based commercial test that has been investigated (Ang et al. 1996) is the ProSpecT® (Alexon Inc, Sunnyvale, CA, USA).

Molecular methods based on detection of E. histolytica-specific DNA by PCR amplification have been developed in recent years. A number of primers designed for E. histolytica-unique genes proved to be useful for the detection of parasites in both stool samples and liver abscess material (Clark and Diamond 1991; Tachibana et al. 1991; Prakash et al. 2000; Zaman et al. 2000). The PCR-based diagnostics of E. histolytica infections although specific and sensitive are not yet widely used. One of the limiting factors is that formalin based fixtives usually used to preserve specimens could interfere with DNA recovery from the sample. Further optimization of sample processing is necessary to allow more common application of molecular techniques.

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