Entamoeba histolytica and Entamoeba dispar

It has now been established that two distinct species, although morphologically identical, exist within what was originally known as Entamoeba histolytica: E. dispar and E. histolytica, for the nonpathogenic and pathogenic forms, respectively (Diamond and Clark 1993). For both diagnostic as well as epidemiological reasons, it is necessary to establish markers to differentiate between the two Entamoeba species. The PCR has shown to be a promising tool for this purpose, since no time-consuming cultivation of the organism is needed.

Tachibani et al. (1991) clarified DNA differences between pathogenic and non-pathogenic isolates of E. histolytica (Tachibani 1991), which has been used to design PCR assays for diagnosis of stool specimen (Rivera et al. 1996; Sanuki et al. 1997). Other gene targets for Entamoeba species-specific single or nested PCR, are the genes for the small subunit rRNA (Clark and Diamond 1991; Katzwinkel-Wladarsch et al. 1994) and the 16S rRNA (Troll et al. 1997). PCR based on extra-chromosomal circular DNA from E. histolytica has also been used to differentiate between the two Entamoeba-species (Acuna-Soto et al. 1993; Aguirre et al. 1995). The latter assay was modified and used in a PCR assay, which was preceded by a rapid extraction procedure and followed by colorimetric product detection, PCR-SHELA (Britten et al. 1997).

Although microscopy remains the method of choice for Entamoeba-detection, specific PCR assays for differentiation between E. dispar and E. histolytica will greatly help the physicians determine whether they must treat the patients or not.

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