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Dientamoeba Fragilis, the Neglected Trichomonad of the Human Bowel

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Dientamoeba Fragilis, the Neglected Trichomonad of the Human Bowel crossmark Dientamoeba fragilis, the Neglected Trichomonad of the Human Bowel Damien Stark,a Joel Barratt,b Douglas Chan,b John T. Ellisb Division of Microbiology, Sydpath, St Vincent’s Hospital, Darlinghurst, NSW, Australiaa; School of Life Sciences and the I3 Institute, University of Technology Sydney, Broadway, NSW, Australiab SUMMARY ..................................................................................................................................................553 INTRODUCTION ............................................................................................................................................553 HISTORICAL ASPECTS ......................................................................................................................................554 TAXONOMY ................................................................................................................................................554 GENETIC DIVERSITY ........................................................................................................................................555 MORPHOLOGICAL CHARACTERISTICS ....................................................................................................................556 Trophozoites .............................................................................................................................................556 Downloaded from Precysts...................................................................................................................................................557 Cysts......................................................................................................................................................558 DIAGNOSTIC TECHNIQUES ................................................................................................................................558 Microscopy ...............................................................................................................................................558 Culture ...................................................................................................................................................559 Immunoassays............................................................................................................................................560 PCR.......................................................................................................................................................560 CLINICAL ASPECTS AND EPIDEMIOLOGY..................................................................................................................562 TRANSMISSION .............................................................................................................................................567 Cysts or Pinworm?........................................................................................................................................567 http://cmr.asm.org/ DIENTAMOEBA CARRIAGE IN ANIMALS ....................................................................................................................568 PATHOGENICITY............................................................................................................................................569 PATHOLOGY................................................................................................................................................570 THERAPY....................................................................................................................................................570 Arsenic-Based Compounds...............................................................................................................................571 Tetracycline and Erythromycin ...........................................................................................................................571 Iodoquinol................................................................................................................................................571 Paromomycin ............................................................................................................................................572 Metronidazole ............................................................................................................................................572 Secnidazole and Ornidazole..............................................................................................................................572 In Vitro Susceptibility Testing .............................................................................................................................572 on May 11, 2016 by guest CONCLUSIONS .............................................................................................................................................573 ACKNOWLEDGMENTS......................................................................................................................................573 REFERENCES ................................................................................................................................................573 AUTHOR BIOS ..............................................................................................................................................579 SUMMARY INTRODUCTION Dientamoeba fragilis is a protozoan parasite of the human bowel, ientamoeba fragilis is a single-celled protozoan parasite commonly reported throughout the world in association with gas- Dlargely ignored by medicine as a cause of human gastrointes- trointestinal symptoms. Despite its initial discovery over 100 years tinal (GI) disease and is often described as a “neglected parasite.” ago, arguably, we know less about this peculiar organism than any Despite regular, continuous reports emerging over the last 100 other pathogenic or potentially pathogenic protozoan that infects years that describe an association between D. fragilis and human humans. The details of its life cycle and mode of transmission are GI disorders, including diarrhea, it is still often ignored as a patho- not completely known, and its potential as a human pathogen is gen, and routine testing may not be routinely conducted by diag- debated within the scientific community. Recently, several major nostic laboratories. Indeed, knowledge on the basic biology of this advances have been made with respect to this organism’s life cycle and molecular biology. While many questions remain unan- swered, these and other recent advances have given rise to some Published 11 May 2016 intriguing new leads, which will pave the way for future research. Citation Stark D, Barratt J, Chan D, Ellis JT. 2016. Dientamoeba fragilis, the This review encompasses a large body of knowledge generated on neglected trichomonad of the human bowel. Clin Microbiol Rev 29:553–580. various aspects of D. fragilis over the last century, together with an doi:10.1128/CMR.00076-15. Address correspondence to Damien Stark, [email protected]. update on the most recent developments. This includes an update D.S. and J.B. contributed equally to this work. on the latest diagnostic techniques and treatments, the clinical Supplemental material for this article may be found at http://dx.doi.org/10.1128 aspects of dientamoebiasis, the development of an animal model, /CMR.00076-15. the description of a D. fragilis cyst stage, and the sequencing of the Copyright © 2016, American Society for Microbiology. All Rights Reserved. first D. fragilis transcriptome. July 2016 Volume 29 Number 3 Clinical Microbiology Reviews cmr.asm.org 553 Stark et al. species is scant at best. As a result, we remain ignorant of this an adult male from England (11). Thus, in the space of 4 years parasite’s host distribution, its life cycle, and many other aspects of following the discovery of D. fragilis, controversy surrounding its its biology. However, recent developments have been made in the pathogenicity arose and persists to this day. field of D. fragilis research, which are changing this profile. The design and development of new, modern diagnostic tests for D. TAXONOMY fragilis have been associated with a major increase in the rate of Jepps and Dobell were the first to not only describe D. fragilis in detection of this parasite in cases of GI disease. This in turn has the literature but also to assign it a taxonomic position (1). In resulted in a reassessment of historical knowledge on D. fragilis, 1918, three Entamoeba species were known to occur in the human particularly its potential role as a human pathogen. This review bowel: the nonpathogenic species Entamoeba coli and Entamoeba focuses on D. fragilis as a cause of human disease and on its diag- nana (now known as Endolimax nana) and the pathogenic species nosis and treatment and provides an update on our current un- Entamoeba histolytica. While this new protozoan was placed in the derstanding of its biology and life cycle. family Entamoebidae, Jepps and Dobell (1) argued that as it had a binucleated form and no cyst stage, it not only was a new species HISTORICAL ASPECTS but also warranted the formation of a new genus. They demon- The distinguished English protozoologist Charles Wenyon is strated that once outside the human body, this organism became credited with the discovery of D. fragilis in 1909 after examining “fragile” and degenerated rapidly. Subsequently, the name Dien- Downloaded from his own parasitological stool preparations. However,
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