Dientamoeba fragilis as a cause of travelers' diarrhea: report of seven cases

Comparison and Recommendations for Use of Dientamoeba fragilis Real-Time PCR Assays

Dientamoeba fragilis is a gastrointestinal trichomonad parasite whose pathogenicity is yet to be determined. The difficulty involved in microscopically diagnosing D. fragilis in feces led to the development of real-time PCR methodologies for the detection of D. fragilis in stool samples. Prevalence studies in Europe show much higher levels of infection where a laboratory-developed real-time assay is the predominant assay for the detection of Dientamoeba fragilis than in regions that use the EasyScreen assay for detection of gastrointestinal pathogens. The aim of this study was to compare a commercially available Dientamoeba fragilis assay (Genetic Signatures EasyScreen assay) to a widely used laboratory-developed real-time PCR method. Two hundred fifty fecal samples were screened using the laboratory-developed real-time assay on four real-time PCR platforms producing a number of discrepant results. Limit-of-detection studies were undertaken to attempt to resolve sensitivity for each platform tested. The presence or absence of Dientamoeba fragilis DNA in discrepant samples was shown using PCR amplicon next-generation sequencing. Eukaryotic 18S diversity profiling was conducted on discrepant samples to identify the presence or absence of additional protozoan species in samples that may be responsible for cross-reactivity seen in these samples. The results revealed the potential for multiple false-positive results when using the laboratory-developed real-time assay across multiple real-time platforms using manufacturer default settings. This report provides recommendations to resolve these issues where possible and suggestions for future prevalence studies, and it emphasizes the EasyScreen assay as the molecular method of choice as well as the need for standardization of detection assays across all nations screening for D. fragilis.

Current treatment options for Dientamoeba fragilis infections

Dientamoeba fragilis belongs to the trichomonad group of protozoan parasites and it has been implicated as a cause of gastrointestinal disease with world-wide prevalences ranging from 0.5% to 16%. The majority of patients with dientamoebiasis present with gastrointestinal complaints. Chronic symptoms are common with up to a third of patients exhibiting persistent diarrhoea. Numerous studies have successfully demonstrated parasite clearance, coupled with complete resolution of clinical symptoms following treatment with various antiparasitic compounds. Treatments reported to be successful for dientamoebiasis include carbarsone, diphetarsone, tetracyclines, paromomycin, erythromycin, hydroxyquinolines and the 5-nitroimidazoles, including metronidazole, secnidazole, tinidazole and ornidazole. It is of note that most current treatment data is based only on small number of case reports. No large scale double blind randomised placebo controlled trials testing the efficacy of antimicrobial agents against D. fragilis has been undertaken highlighting the need for further study. In addition there is very little in vitro susceptibility data available for the organism making some current treatment options questionable. The aim of this review is to critically discuss all treatment options currently available for dientamoebiasis.

Enteric protozoa in the developed world: a public health perspective

Several enteric protozoa cause severe morbidity and mortality in both humans and animals worldwide. In developed settings, enteric protozoa are often ignored as a cause of diarrheal illness due to better hygiene conditions, and as such, very little effort is used toward laboratory diagnosis. Although these protozoa contribute to the high burden of infectious diseases, estimates of their true prevalence are sometimes affected by the lack of sensitive diagnostic techniques to detect them in clinical and environmental specimens. Despite recent advances in the epidemiology, molecular biology, and treatment of protozoan illnesses, gaps in knowledge still exist, requiring further research. There is evidence that climate-related changes will contribute to their burden due to displacement of ecosystems and human and animal populations, increases in atmospheric temperature, flooding and other environmental conditions suitable for transmission, and the need for the reuse of alternative water sources to meet growing population needs. This review discusses the common enteric protozoa from a public health perspective, highlighting their epidemiology, modes of transmission, prevention, and control. It also discusses the potential impact of climate changes on their epidemiology and the issues surrounding waterborne transmission and suggests a multidisciplinary approach to their prevention and control.

New advances in the in-vitro culture of Dientamoeba fragilis

SUMMARYDientamoeba fragilis is an intestinal protozoan in humans that is commonly associated with diarrhoea and other gastrointestinal complaints. Studies conducted to investigate the biology of this parasite are limited by methods for in vitro cultivation. The objective of this study was to improve a biphasic culture medium, based on the Loeffler's slope, by further supplementation in order to increase the yield of trophozoites in culture. The current in vitro culture of D. fragilis is a xenic culture with a mix of bacteria. Three different liquid overlays were evaluated including Earle's balanced salt solution (EBSS), PBS and Dulbecco's modified PBS (DPBS), for their ability to support the in vitro growth of D. fragilis trophozoites. Out of these 3 overlays EBSS gave the highest increase in the trophozoite numbers. The effect of supplementation was analysed by supplementing EBSS with ascorbic acid, ferric ammonium citrate, L-cysteine, cholesterol and alpha-lipoic acid and quantification of in vitro growth by cell counts. A new liquid overlay is here described based upon EBSS supplemented with cholesterol and ferric ammonium citrate that, in conjunction with the Loeffler's slope, supports the growth of D. fragilis trophozoites in vitro. This modified overlay supported a 2-fold increase in the numbers of trophozoite in culture from all 4 D. fragilis isolates tested, when compared to a PBS overlay. These advances enable the harvest of a larger number of trophozoites needed for further studies on this parasite.

A case-controlled study of Dientamoeba fragilis infections in children

Dientamoeba fragilis is a pathogenic protozoan parasite that is implicated as a cause of human diarrhoea. A case-controlled study was conducted to determine the clinical signs associated with D. fragilis infection in children presenting to a Sydney Hospital. Treatment options are also discussed. Stool specimens were collected from children aged 15 years or younger and analysed for the presence of D. fragilis. In total, 41 children were included in the study along with a control group. Laboratory diagnosis was performed by microscopy of permanently stained, fixed faecal smears and by real-time PCR. Gastrointestinal symptoms were present in 40/41 (98%) of these children with dientamoebiasis, with diarrhoea (71%) and abdominal pain (29%) the most common clinical signs. Chronic gastrointestinal symptoms were present in 2% of cases. The most common anti-microbial used for treatment was metronidazole (n=41), with complete resolution of symptoms and clearance of parasite occurring in 85% of cases. A treatment failure rate occurred in 15% of those treated with metronidazole. Follow-up treatment comprised of an additional course of metronidazole or iodoquinol was needed in order to achieve complete resolution of infection and symptoms in this group. This study demonstrates the pathogenic potential of D. fragilis in children and as such it is recommended that all laboratories must routinely test for this organism and treat if detected.

Newly defined conditions for the in vitro cultivation and cryopreservation of Dientamoeba fragilis: new techniques set to fast track molecular studies on this organism

Dientamoeba fragilis is a pathogen of the human gastrointestinal tract that is a common cause of diarrhoea. A paucity of knowledge on the in vitro cultivation and cryopreservation of Dientamoeba has meant that few studies have been conducted to investigate its biology. The objective of this study was to define, for the first time, in vitro culture conditions able to support the long-term in vitro growth of Dientamoeba. Also, we aimed to define a suitable method for cryopreserving viable Dientamoeba trophozoites. A modified BD medium, TYGM-9, Loeffler's slope medium, Robinson's medium, Medium 199, Trichosel and a Tritrichomonas fetus medium were compared, using cell counts, for their ability to support the growth of D. fragilis at various temperatures and atmospheric conditions. Loeffler's slope medium supported significantly better growth compared to other media. A temperature of 42°C and a microaerophilic atmosphere were also optimum for Dientamoeba growth. To our knowledge, this is the first study to describe and compare different culture media and conditions for the growth of clinical isolates of D. fragilis. This new technology will aid the development of diagnostics for dientamoebiasis as well as facilitate large-scale sequencing projects that will fast track molecular studies on D. fragilis.

Comparison of microscopy, two xenic culture techniques, conventional and real-time PCR for the detection of Dientamoeba fragilis in clinical stool samples

Dientamoeba fragilis is a pathogenic protozoan parasite that is notoriously difficult to diagnose. The aim of this study was to determine the gold standard for laboratory detection of D. fragilis. A total of 650 human faecal samples were included in the study. All specimens underwent the following: microscopy using a permanent stain (modified iron-haematoxylin), culture using a modified Boeck and Drbohlav's medium (MBD) and TYGM-9, a conventional polymerase chain reaction (PCR) and a real-time PCR (RT-PCR). The overall prevalence of D. fragilis in the study population was 5.4% (35/650). RT-PCR detected 35 isolates, conventional PCR detected 15 isolates, MBD culture detected 14 isolates, TYGM-9 detected ten isolates, while microscopy detected 12 isolates. RT-PCR detected an additional 15 positive samples compared to the other diagnostic methods, all of which were confirmed by sequencing. When all methods were compared to each other, RT-PCR showed a sensitivity and specificity of 100 and 100%, conventional PCR 42.9 and 100%, MBD culture 40 and 100%, TYGM-9 culture 28.6 and 100%, and microscopy 34.3 and 99%, respectively. These results show that RT-PCR is the diagnostic method of choice for the detection of D. fragilis in clinical samples and, as such, should be considered as the gold standard for diagnosis.

Parasitological diagnosis combining an internally controlled real-time PCR assay for the detection of four protozoa in stool samples with a testing algorithm for microscopy

Molecular detection of gastrointestinal protozoa is more sensitive and more specific than microscopy but, to date, has not routinely replaced time-consuming microscopic analysis. Two internally controlled real-time PCR assays for the combined detection of Entamoeba histolytica, Giardia lamblia, Cryptosporidium spp. and Dientamoeba fragilis in single faecal samples were compared with Triple Faeces Test (TFT) microscopy results from 397 patient samples. Additionally, an algorithm for complete parasitological diagnosis was created. Real-time PCR revealed 152 (38.3%) positive cases, 18 of which were double infections: one (0.3%) sample was positive for E. histolytica, 44 (11.1%) samples were positive for G. lamblia, 122 (30.7%) samples were positive for D. fragilis, and three (0.8%) samples were positive for Cryptosporidium. TFT microscopy yielded 96 (24.2%) positive cases, including five double infections: one sample was positive for E. histolytica/Entamoeba dispar, 29 (7.3%) samples were positive for G. lamblia, 69 (17.4%) samples were positive for D. fragilis, and two (0.5%) samples were positive for Cryptosporidium hominis/Cryptosporidium parvum. Retrospective analysis of the clinical patient information of 2887 TFT sets showed that eosinophilia, elevated IgE levels, adoption and travelling to (sub)tropical areas are predisposing factors for infection with non-protozoal gastrointestinal parasites. The proposed diagnostic algorithm includes application of real-time PCR to all samples, with the addition of microscopy on an unpreserved faecal sample in cases of a predisposing factor, or a repeat request for parasitological examination. Application of real-time PCR improved the diagnostic yield by 18%. A single stool sample is sufficient for complete parasitological diagnosis when an algorithm based on clinical information is applied.