Introduction

Dientamoeba fragilis is a protozoan of the human digestive tract, yet its pathogenic role remains poorly understood. Fecal microbiota transplantation (FMT) provides a useful model for investigating the potential pathogenicity and transmission of this protist from donor to recipient. Donor selection is highly stringent, and the presence of D. fragilis is subject to controversy as an exclusion criterion [1-4].

Aims & Methods

This study aimed to determine the prevalence of D. fragilis in both FMT donors and recipients and to evaluate its potential impact on the efficacy and safety of FMT as a treatment for recurrent Clostridioides difficile infection (rCDI). This single-center, longitudinal cohort study analyzed stool samples from FMT donors and recipients at three time points: pre-treatment and at 2 and 8 weeks post-FMT. All samples were negative for D. fragilis on direct microscopy and were retrospectively tested using real-time (RT-PCR). CDI cure rates, gastrointestinal adverse events (AE), and serious adverse events (SAE) were assessed prospectively.

Results

A total of 53 FMT were administered to 47 different patients, with 23 of 53 (43%) derived from D. fragilis-positive donor stool (4 out of 10 donors, 40%). One recipient tested positive before FMT (1/47, 2.1%). Among 22 patients initially negative for D. fragilis who received stool from D. fragilis-positive donors, four (18.2%) tested positive on day 15 post-FMT and remained positive at week 8. None of the recipient with D. fragilis-negative FMT was tested positive. No significant differences in efficacy, AE, or SAE were observed between recipients of FMT from D. fragilis-positive versus -negative donors, even in severely immunocompromised patients. No SAE could be attributed to FMT.

Conclusion

This study suggests that D. fragilis can be transmitted through FMT without significant clinical impact in terms of efficacy and safety. These findings argue for reconsidering the exclusion of positive donors and support the lack of pathogenicity of D. fragilis.

References

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2. Cacciò SM. Molecular epidemiology of Dientamoeba fragilis. Acta Trop 2018 ; 184:73–77.
3. Shasha D, Grupel D, Treigerman O, et al. The clinical significance of Dientamoeba fragilis and Blastocystis in human stool—retrospective cohort study. Clin Microbiol Infect 2024 ; 30:130–136.
4. Terveer EM, Gool T van, Ooijevaar RE, et al. Human Transmission of Blastocystis by Fecal Microbiota Transplantation Without Development of Gastrointestinal Symptoms in Recipients. Clin Infect Dis 2019 ; 71:2630–2636.