J Clin Pathol 64:933-935 doi:10.1136/jcp.2011.089326
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  • Correspondence

Molecular identification of Pentatrichomonas hominis in two patients with gastrointestinal symptoms

  1. Eric Viscogliosi1
  1. 1Center for Infection and Immunity of Lille, Institut Pasteur de Lille, Inserm U1019, CNRS UMR 8204, University Lille Nord de France, Lille, France
  2. 2Department of Biomedical Sciences, Division of Experimental and Clinical Microbiology, University of Sassari, Sassari, Italy
  3. 3Hôpital Bretonneau, Service de Parasitologie-Mycologie-Médecine Tropicale, Tours, France
  4. 4Hôpital Clocheville, Service de Pédiatrie, Tours, France
  5. 5CHI de Poissy/Saint-Germain-en-Laye, Service de Pathologie, Saint-Germain-en-Laye, France
  1. Correspondence to Eric Viscogliosi, Center for Infection and Immunity of Lille (CIIL), Institut Pasteur de Lille, Inserm U1019, CNRS UMR 8204, University Lille-Nord de France, Biology and Diversity of Emerging Eukaryotic Pathogens, 1 rue du Professeur Calmette, BP 245, 59019 Lille cedex, France; eric.viscogliosi{at}


The trichomonad species Pentatrichomonas hominis colonises the gastrointestinal tract and is generally considered as a commensal organism in humans. However, some studies have recognised an association between diarrhoea and P hominis infection in dogs and cats.1 2 In the present report, we have identified this species using molecular tools in two patients with gastrointestinal troubles. Our data suggest that P hominis is a possible zoonotic species with a significant potential of transmission by water and could be the causative agent of intestinal symptoms in children.

Case reports

An adult (case 1) was followed up for different pathologies including irritable bowel syndrome (IBS). Diarrhoeic stools of the patient were examined and were negative for intestinal parasites. Filter paper/slant culture technique for the recovery of Strongyloides stercoralis larval-stage nematodes from fresh faeces was performed. After 5 days, microscopic examination of the stool culture using merthiolate-iodine-formalin and RAL555 stains did not detect larval nematodes but numerous flagellates, provisionally identified as trichomonads (figure 1A,B). Although no treatment against trichomonads was administered to the patient, the stool examinations performed afterwards did not reveal trichomonads or other parasites.

Figure 1

Cytological appearance of trichomonad cells in stool culture (case 1). (A) Merthiolate-iodine-formalin- and (B) RAL555-stained smears showing numerous trichomonad cells (arrows). Note the round shape of the micro-organisms. Typical microtubular cytoskeletal structures of trichomonads including flagella and axostyle–pelta complex are not visible. Bar=15 μm.

A young child (case 2) presented with abdominal pain and loose stools without fever. A stool sample was examined by direct light microscopy and showed numerous cells assumed to be trichomonad organisms. Additional investigations did not reveal the presence of coinfecting intestinal parasites or pathogenic bacteria. The child was treated with metronidazole (30 mg/kg body weight/day) for 5 days. Treatment was rapidly followed by the clearance of the parasite in subsequent stool tests and the absence of gastrointestinal symptoms.


Two trichomonad species have been isolated from the human intestinal tract: Dientamoeba fragilis and P hominis. Only the former species is considered pathogenic. Regarding P hominis, its host range appears to be very wide since it colonises the gastrointestinal tract of a number of mammalian hosts. To our knowledge, there are only a handful of reports on P hominis mean prevalence in humans. It does not exceed 1–1.5% in Australian Aboriginal communities3 or in adolescent girls, pregnant women and commercial sex workers in Zambia.4 It was suggested that this trichomonad is, in most instances, a harmless commensal organism of the digestive tract. In other mammals, several investigators have recognised a possible association between feline and canine large-bowel diarrhoea and P hominis infection.1 2

In order to identify the trichomonad species found in stool culture (case 1) or stool samples (case 2) from the two patients, the internal transcribed spacer 1 (ITS1)-5.8S rRNA-ITS2 region was amplified from DNA extracted from these samples as described elsewhere.5 Following cloning of the PCR products, 10 clones were arbitrarily selected for each sample and sequenced on both strands. The clones from strains PM (case 1) and KGB (case 2) exhibited 98.3–100% sequence identity strongly suggesting that they were all derived from the same species (figure 2). These sequences also exhibited 98.9–99.6% identity to homologous sequences from P hominis strains available from different hosts. These results unequivocally identified trichomonads found in the digestive tract of the two patients as P hominis and suggested that the same P hominis species could possibly colonise many mammal species, including dogs, bovid and humans. Consequently, our data raised the crucial question of the as-yet-unknown zoonotic potential of P hominis, which is frequently found in pets. Other trichomonad species such as Tritrichomonas foetus5 and Tetratrichomonas sp.6 have an animal reservoir and are also able to colonise humans.

Figure 2

Alignment of sequences of the ITS1-5.8S rRNA-ITS2 region of clones obtained in this study (PM and KGB strains from case 1 and case 2, respectively) and those of trichomonad species of interest found in humans (Trichomonas vaginalis) and animals (Tritrichomonas foetus). The low number of differences (up to four) observed between the clones of the same Pentatrichomonas hominis strain was likely due to the expected variation within the multiple copies of the RNA genes in any given genome. In the common part of our alignment (335 positions including gaps), the sequences of strains PM and KGB exhibited 74.8–75.4%, 59.6–60.2% and 98.9–99.6% identity to homologous sequences from T vaginalis, T foetus and P hominis strains isolated from dogs, bovid and humans. Differences between the clones obtained in this study and differences between these clones and the homologous sequences of P hominis strains isolated from different hosts are shaded (14 variable positions in the common part of the alignment). The nucleotide sequences obtained in this study have been deposited in GenBank under accession numbers HM853978 to HM853987. The sequences of the primers used in this study are underlined. Gaps are represented by asterisks. SSU, small subunit; LSU, large subunit.

In the stool culture of the first patient, P hominis cells were observed exhibiting a round shape in merthiolate-iodine-formalin- and RAL555-stained smears (figure 1A,B). Typical microtubular structures of trichomonads (flagella, axostyle–pelta) were not visible, suggesting that the observed cells represented pseudocysts.7 The main mode of transmission of P hominis is the likely consumption of contaminated food and water through the standard faecal–oral route. Since this species does not form true cysts, vegetative cells have to survive for some time in the environment. In the experimental conditions of filter paper/slant cultures performed in the present work, trichomonads were growing in distilled water at 25°C and remained viable for at least 10 days, suggesting a relatively prolonged P hominis survival in water and, consequently, a significant potential of this species to use waterborne routes of transmission.

As described above, P hominis was the probable causative agent of gastrointestinal troubles in the child (case 2). Indeed, the child did not present other gastrointestinal pathogens and metronidazole treatment led to clearance of trichomonads and clinical recovery. By contrast, in the first patient, IBS was likely to be the main source of intestinal symptoms and probably represented favourable conditions for the development of P hominis infection as a secondary event, since we observed the clearance of trichomonad cells after IBS treatment without antiparasitic treatment. Until now, this trichomonad has been described as a potential aetiological agent of child diarrhoea3 8 (as in case 2), and only rarely in adults. Evidence suggests that more children than adults appear to harbour P hominis, possibly due to children having less strict personal hygiene and the as-yet-unknown increased child susceptibility to the pathogenic effects of this parasite.

Take-home messages

  • Pentatrichomonas hominis is a possible zoonotic species with a significant potential of transmission by the waterborne route and could be the aetiological agent of gastrointestinal troubles in children.

  • The difficulty in identifying pseudocysts of P hominis in stool samples could explain the underestimation of this protozoan infection in humans.


  • Details have been removed from these case descriptions to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.

  • Funding DM was supported by grants from the ERASMUS Programme and Regione Autonoma della Sardegna, and CM by a grant from the Ministère Français de l'Education Nationale, de la Recherche et de la Technologie.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.