Characterisation of polymorphic DNA and its application to typing of Entamoeba histolytica and Entamoeba dispar

A key question in amoebiasis is whether the variable symptoms of amoebic infections are a reflection of different strains of E. histolytica. To address this, tools that allow typing of E. histolytica isolates are needed and this objective formed the basis of the present study. A method for PCR-based DNA typing of E. histolytica isolates has been developed using multiple loci with internal short tandem repeats (STRs) as the polymorphic markers. It has been shown that E. dispar isolates can also be typed by this approach and species-specific primers have been developed for two loci. E. histolytica and E. dispar samples from a wide geographic range were studied to validate the general utility of these loci. Results revealed that E. histolytica is genetically highly variable. This was evident in all the communities studied. E. dispar also displays intra-species variation. The patterns seen for individual strains of both species were stable over time in the same infection. With few exceptions a single E. histolytica or E. dispar strain was identified in samples from infected family groups and outbreaks. Our results show both the existence of mixed species infection as well as the possibility of co-infection with different strains of the same species.