Real Time PCR for Dientamoeba fragilis: a comparison between molecular and microscopical approach

Introduction. Dientamoeba fragilis is an intestinal protozoan parasite that is attracting growing interest. Several authors have associated the presence of this faecal agent to numerous intestinal and systemic clinical symptoms, even though asymptomatic carriers have been reported.Actually, to perform the coproparasitology exam for the identification of D. fragilis it is necessary to recur to an expert microscopist. Recently, several real-time TaqMan assays for the detection of D. fragilis has been reported. In this work we validate an original real-time PCR (TaqMan), re-evaluating the traditional microscopic diagnosis. Moreover, the potential for quantitative information, intrinsic of this molecular technique, was preliminarly explored. Methods. Forty-six carriers of D. fragilis were selected from patients referred to the Service of Microbiology of Padova University Hospital. The parasite was preliminarily detected on several occasions in each patient using traditional microscopy. A control group included forty-two healthy volunteers. Real-time PCR was applied to a stool sample from each subject. On the same sample, gel-electrophoresis amplicon detection PCR and microscopic examination were also performed. Results. The sensitivity of real-time PCR was 100%, whereas microscopy showed 93% sensitivity (direct wet mount on fixed stools and trichrome stain), gel-electrophoresis PCR 76% and Giemsa stain 52%.The specificity of all methods was 100%. On the quantitative side, the frequency distribution of the protozoan load of the stools revealed a near to log-normal pattern is apparent for the data yielded by real-time PCR. Conclusions. The real-time PCR was clearly superior to either the gel electrophoresis PCR or the traditional microscopic examination. Just one unpreserved stool sample was adequate to find the parasite. The entire procedure could be performed within a few hours avoiding toxic dyes.