Clinical significance of Dientamoeba fragilis and Blastocystis: Lessons from clinical trials, cohort studies, and faecal microbiota transplantation - a narrative review.

Authors

Ludovico Cobuccio, Keyvan Moser, Damien Jacot, Nathalie Kapel, Anastasios D Tsaousis, Tatiana Galperine

Published in

Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases. Oct 06, 2026. Epub Oct 06, 2026.

Abstract

The adoption of highly sensitive syndromic multiplex PCR panels led to an increase in Blastocystis and Dientamoeba fragilis detection, two of the most commonly identified intestinal protists worldwide. With positivity rates of 15-25% on syndromic gastrointestinal panels, a positive result frequently triggers antimicrobial treatment despite uncertain clinical significance.
To synthesise multi-dimensional evidence on the pathogenicity of Blastocystis and D. fragilis from multiple lines of investigation and to propose a pragmatic clinical decision framework for interpreting positive test results.
A systematic search of PubMed/MEDLINE (inception to January 2026) was conducted using structured queries for Blastocystis and D. fragilis across thematic blocks: epidemiology, molecular diagnosis, pathogenicity mechanisms, clinical trials, faecal microbiota transplantation (FMT), and microbiome associations. No language restriction was applied. Study selection prioritised randomised controlled trials, prospective FMT cohorts, large-scale metagenomic analyses, and systematic reviews. Reference lists of retrieved articles were manually screened.
Current evidence suggests asymptomatic carriage is the biological norm for both organisms, and no specific subtypes, genotypes, or parasite load thresholds have been consistently linked to disease. Three placebo-controlled randomised controlled trials (RCTs) showed no treatment benefit: two conducted in paediatric populations and one an adult pilot study. FMT cohort studies demonstrate safe transmission without adverse events. Metagenomic analyses of nearly 57,000 individuals have identified an association between Blastocystis carriage, greater microbial diversity, and more favourable cardiometabolic profiles, although the direction and causality of these relationships remain unclear.
In immunocompetent hosts, detection of Blastocystis or D. fragilis does not indicate disease; for Blastocystis in particular, carriage should be regarded as an ecological marker of the intestinal microbiota. A clinical decision algorithm is proposed in which reassurance is the default, treatment is reserved for exceptional circumstances (severe immunosuppression or chronic unexplained symptoms after thorough exclusion of alternative diagnoses), and clinical response, not PCR clearance, serves as the only meaningful endpoint.

PMID:
42838172
Bibliographic data and abstract were imported from PubMed on 07 Oct 2026.

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