**7. Role of genetic characteristics of the infecting strains in the pathogenesis of dientamoebiasis**

The outcome of an infection may depend on several factors, among which the genetic charac‐ teristics of the specific pathogen have been identified as an important one. The virulence and disease outcome has been linked to the genotypes of few parasites such as *Entamoeba histoly‐ tica* and *Giardia lamblia* [116–124]. Despite its inability to ascertain correlation between geno‐ type and disease outcome, evidence emerged using the ssu rRNA gene of at least two genetically distinct variants (genotypes 1 and 2) of *D. fragilis* are in existence [6, 9, 20, 125, 126]. Thus, in the case of *D. fragilis* infections, the ssu rRNA gene demonstrated inferiority as a tool for molecular epidemiological studies [127]. Accordingly, new molecular tools were employed to demonstrate the association between variants and clinical disease outcome. One such tool is the use of C-profiling in which the cysteine nucleotide pattern is compared between samples for evidence of genetic variation on the internal transcribed spacer regions (ITS1 and ITS2) of the ribosomal gene [128]. These regions are noncoding sequences reported to be suitable for molecular characterization of phylogenetically related organisms [129]. Bart et al. (2008) and Stark and his group (2009) documented the occurrence in variations of ITS1 in *D. fragilis* isolates [21, 130]. Furthermore, a correlation between certain ITS1 variants and disease outcome was reported [130]. Recently, Barratt et al. (2010) found that the growth of Dienta‐ moeba in certain media formulations varied between different isolates, and while all Dienta‐ moeba isolates described by Barratt and colleagues were from patients with gastrointestinal complaints, this work indicates that phenotypic diversity exists in Dientamoeba and that the variation noted is likely to have a genetic basis. Nevertheless, it is still unclear whether the two genotypes differ in their pathogenicity [131].
