PCR fingerprinting of Blastocystis isolated from symptomatic and asymptomatic human hosts

Comparative molecular prevalence and subtypes distribution of Blastocystis sp. a potentially zoonotic infection isolated from symptomatic and asymptomatic patients in Iran: A systematic review and meta-analysis

PURPOSE

The present systematic review and meta-analysis was aimed to assess the weighted molecular prevalence of Blastocystis sp. in humans along with the comparative molecular prevalence and subtypes distribution of Blastocystis isolated from symptomatic and asymptomatic patients in Iran.

METHODS

International electronic databases including Medline/PubMed, ProQuest, Scopus, Embase, and Google Scholar were explored until 4th October 2020. Heterogeneity index was evaluated among studies using Cochran's Q test and I² index. Finally, 23 eligible studies were qualified to be included in this review.

RESULTS

The pooled molecular prevalence of Blastocystis sp. in Iran was reported 15.2% (95% CI 11.5-19.7). In addition, the molecular prevalence based on PCR-sequencing and STS primers was reported 12.5% (95% CI 8.6-17.7) and 19.8% (95% CI 13.1-28.8), respectively. Interestingly, there was a considerably higher prevalence among asymptomatic patients [25.1% (95% CI 20.8-30.0)] in comparison to symptomatic ones [21.0% (95% CI 15.9-27.2)]. In addition, the frequency of Blastocystis ST1, ST2, and ST3 from positive samples in symptomatic patients was 19.7%, 35.1%, and 47.4%, respectively. In addition, the prevalence of Blastocystis ST1, ST2, and ST3 from positive samples in asymptomatic patients was 27.1%, 26.8%, and 37.8%, respectively. The results obtained in Iran showed that Blastocystis is more common in asymptomatic patients compared to patients having clinical symptoms. Of note, ST3, as the most common subtype causing clinical symptoms, was the most prevalent reported subtype among both symptomatic and asymptomatic patients in the country.

CONCLUSIONS

Hence, the pathogenicity of the Blastocystis parasite is not subtype-specific and appears to be related to a variety of risk factors. Still the Blastocystis epidemiology is open to question and more large-scale studies should be performed on this aspect.

Subtyping of Blastocystis sp. isolated from symptomatic and asymptomatic individuals in Makkah, Saudi Arabia

BACKGROUND

Blastocystis is a group of cosmopolitan gastrointestinal parasite of humans and a wide variety of animals. These anaerobic protozoans include more than 17 specific small-subunit ribosomal RNA subtypes, of which nine are found in humans with a variable geographical distribution. Until now, no study has described the Blastocystis subtypes present in Saudi Arabia.

METHODS

In total, 1,262 faecal samples were collected from patients with gastrointestinal complaints and asymptomatic individuals visiting two major hospitals. All samples were analysed by F1/R1 diagnostic PCR, microscopy and culture methods. The subtypes of Blastocystis sp. isolates were determined by the sequenced-tagged site (STS)-based method.

RESULTS

One-hundred-thirty-three positive cases were detected by F1/R1 diagnostic PCR, of which 122 were also positive by the culture method and 83 by direct microscopy. The sensitivities of direct microscopy and the culture method were 62% and 92%, respectively. Subtype (ST3) was the most prevalent (80.5%), followed by ST1 (14.5%) and ST2 (5%). ST4, ST5, ST6 and ST7 were not detected in this study. ST3 infections were significantly predominant (P < 0.05) among symptomatic patients.

CONCLUSIONS

To our knowledge, this study provides the first run-through information on Blastocystis sp. epidemiology in Makkah city, revealing a rather moderate prevalence of 10.5% and the presence of three subtypes, ST1, ST2, and ST3. ST3 was the most predominant, particularly among symptomatic patients.

Features of Blastocystis spp. in xenic culture revealed by deconvolutional microscopy

Blastocystis spp. are common human enteric parasites with complex morphology and have been reported to cause irritable bowel syndrome (IBS). Deconvolutional microscopy with time-lapse imaging and fluorescent spectroscopy of xenic cultures of Blastocystis spp. from stool samples of IBS patients and from asymptomatic, healthy pigs allowed observations of living organisms in their natural microbial environment. Blastocystis organisms of the vacuolated, granular, amoebic and cystic forms were observed to autofluorescence in the 557/576 emission spectra. Autofluorescence could be distinguished from fluorescein-conjugated Blastocystis-specific antibody labelling in vacuolated and granular forms. This antibody labelled Blastocystis subtypes 1, 3 and 4 but not 5. Surface pores of 1 μm in diameter were observed cyclically opening and closing over 24 h. Vacuolated forms extruded a viscous material from a single surface point with coincident deflation that may demonstrate osmoregulation. Tear-shaped granules were observed exiting from the surface of an amoebic form, but their origin and identity remain unknown.

Blastocystis subtypes in symptomatic and asymptomatic family members and pets and response to therapy

BACKGROUND

Blastocystis is a common, enteric parasite. The pathogenicity of the organism is uncertain, but subtypes (ST) 1 and 3 have been reported more likely to cause irritable bowel-like symptoms.

AIMS

We treated symptomatic patients positive for Blastocystis with conventional therapy and analysed 16 small-subunit (SSU) rDNA to assess clearance and carriage rates and ST prevalence of the parasite in the asymptomatic household members.

METHODS

In a longitudinal, prospective case study, 11 symptomatic patients positive for Blastocystis underwent outpatient clinical assessment to exclude other diagnoses before 14 days of either metronidazole 400 mg three times daily or trimethoprim/sulfamethoxazole 160/800 mg twice-daily therapy. Faecal specimens were collected from patients at baseline, day 15, 28 and 56 after therapy and from 17 family members and eight pets at day 15. Specimens were analysed using faecal smear, culture and polymerase chain reaction analysis of 16SSU rDNA.

RESULTS

No patient cleared the organism following therapy. ST 1 (45%), 3 (36%), 4 (36%) and 6 (9%) were found in the symptomatic Blastocystis patients, and ST identified before and after therapy were identical in each individual. All household contacts were positive for Blastocystis and 16/17 (94%) contacts showed identical Blastocystis ST to the symptomatic family member. All pets were positive for Blastocystis with polymerase chain reaction testing, 7/8 (88%) demonstrating ST concordance with the symptomatic Blastocystis patients.

CONCLUSIONS

Conventional therapy is ineffective for symptomatic Blastocystis infection. The high prevalence of Blastocystis infection within households suggested transmission between humans and their pets. Subtyping analysis of SSU rDNA alone in Blastocystis does not appear to predict pathogenicity.

Urinary hyaluronidase activity in rats infected with Blastocystis hominis--evidence for invasion?

The fact whether Blastocystis hominis can invade has always been in question. Apart from a few sporadic studies such as that done on gnotobiotic guinea pigs which showed surface invasion and mucosal inflammation of the host's intestine caused by B. hominis infection, no real documentation of invasion has been proven. Studies have shown that hyaluronidase is secreted during the penetration into the host's skin and gut by nematode parasites. Hyaluronidase activity in protozoa namely Entamoeba histolytica has also been described previously. This study attempts to determine hyaluronidase in urine samples of B. hominis-infected rats. The presence of hyaluronidase in urine provides an indirect evidence of invasion by B. hominis into colonic epithelium causing the degradation of extracellular matrix proteins namely hyaluronic acid (HA). HA is depolymerized by hyaluronidase which may be used by organisms to invade one another. In this study, the levels of urinary hyaluronidase of Sprague-Dawley rats infected with B. hominis were monitored for 30 days. Hyaluronidase levels in the infected rats were significantly higher on days 28 and 30 compared to the day before inoculation (P < 0.01 and P < 0.05, respectively). During this stage, parasitic burden in infected stools was also at a high level. Proinflammatory cytokines, interleukin-6 and interleukin-8, were also significantly higher (P < 0.05) in the serum of infected rats. The study demonstrates that since no other pathogen was present and that amoeboid forms of the parasites have been shown to exist previously, the elevated levels of hyaluronidase in this preliminary finding suggests that the organism is capable of having invasion or penetration activity in the hosts' intestine.

Differences in clinical significance and morphologic features of Blastocystis sp subtype 3

Blastocystis is a polymorphic intestinal parasite that is common in humans. A total of 51 asymptomatic and symptomatic patients positive for Blastocystis only were included in the study. Symptoms were mainly nonspecific gastrointestinal symptoms. Blastocystis isolates were xenically cultured and subtyped. Blastocystis species subtype 3 was the predominant subtype. Intrasubtype differences (vacuolar/amoeboid presence) in subtype 3 morphotypes were observed in 32 asymptomatic and symptomatic subtype 3 cases and could possibly be related to Blastocystis pathogenic potential. Diverse morphologic features (vacuolar transiting to amoeboid), probably reflecting the progression from an asymptomatic to a symptomatic state, were observed in an asymptomatic subtype 3 carrier who later had symptoms. Searching for amoeboid forms might be helpful to presumptively screen symptomatic patients with subtype 3 or to follow up an asymptomatic subtype 3 carrier in case symptoms become evident before antiprotozoal treatment was attempted. Further studies on the roles of morphologic features and variation within Blastocystis species subtypes as predictors of symptoms are encouraged.

PCR-based subtyping of Blastocystis isolates from symptomatic and asymptomatic individuals in a major hospital in Ankara, Turkey

The stool samples obtained from 94 patients with gastrointestinal symptoms and 109 asymptomatic individuals, who checked in due to other reasons, admitted at a major hospital in Ankara, Turkey were examined with native Lugol's iodine, trichrome, and Kinyoun's acid-fast stainings for parasitology examinations and with in vitro culture method for detection of Blastocystis. In a total of 203 stool samples tested, native Lugol's iodine and trichrome stainings could detect 12 (5.9%) and 20 (9.9%) positive samples for Blastocystis, respectively. Conversely, culture method could detect 66 (32.5%) positive samples, and this method was more sensitive compared to the both microscopic examinations (p < 0.001). Among 66 positive samples for Blastocystis, 27 were from symptomatic patients and 39 were from asymptomatic group. Subtypes (STs) were determined by PCR using seven different sequence-tagged site primers. ST3 was the most dominant in both symptomatic and asymptomatic groups and followed by ST1 or ST2. There were mixed infections with STs 1 and 2 or STs 1 and 3 in nine isolates. There was no statistical significance of the distribution of Blastocystis sp. subtypes between symptomatic and asymptomatic individuals (p > 0.05).

Blastocystis: unravelling potential risk factors and clinical significance of a common but neglected parasite

Two independent studies were conducted to describe symptoms and potential risk factors associated with Blastocystis infection. Isolates were subtyped by molecular analysis. In the NORMAT study (126 individuals randomly sampled from the general population) 24 (19%) were positive for Blastocystis. Blastocystis was associated with irritable bowel syndrome (P=0.04), contact with pigs (P<0.01) and poultry (P=0.03). In the Follow-up (FU) study (follow-up of 92 Blastocystis-positive patients), reports on bloating were associated with subtype (ST) 2 (P<0.01), and blood in stool to mixed subtype infection (P=0.06). ST1 was more common in FU individuals (32%) than in NORMAT individuals (8%), whereas single subtype infections due to ST3 or ST4 were seen in 63% of the NORMAT cases and 28% of the FU cases. Only FU individuals hosted ST7, and ST6/7 infections due to ST7 or ST9 were characterized by multiple intestinal symptoms. The data indicate subtype-dependent differences in the clinical significance of Blastocystis.

Pursuing the clinical significance of Blastocystis--diagnostic limitations

The clinical significance of one of the most prevalent single-celled intestinal parasites worldwide, Blastocystis, remains unsettled. A plethora of clinical and epidemiological studies have been undertaken to generate data on its prevalence in different populations and investigate the role of the parasite as a cause of gastro- and extra-intestinal disease. In this article, we pinpoint limitations of studies that seek to determine the clinical significance of Blastocystis, based on shortcomings in our understanding of Blastocystis diagnosis and biology, and identify methodologies for further studies aimed at determining the molecular epidemiology and clinical impact of this parasite.

Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection

Blastocystis is a prevalent enteric protozoan that infects a variety of vertebrates. Infection with Blastocystis in humans has been associated with abdominal pain, diarrhea, constipation, fatigue, skin rash, and other symptoms. Researchers using different methods and examining different patient groups have reported asymptomatic infection, acute symptomatic infection, and chronic symptomatic infection. The variation in accounts has lead to disagreements concerning the role of Blastocystis in human disease, and the importance of treating it. A better understanding of the number of species of Blastocystis that can infect humans, along with realization of the limitations of the existing clinical laboratory diagnostic techniques may account for much of the disagreement. The possibility that disagreement was caused by the emergence of particular pathogenic variants of Blastocystis is discussed, along with the potential role of Blastocystis infection in irritable bowel syndrome (IBS). Findings are discussed concerning the role of protease-activated receptor-2 in enteric disease which may account for the presence of abdominal pain and diffuse symptoms in Blastocystis infection, even in the absence of fever and endoscopic findings. The availability of better diagnostic techniques and treatments for Blastocystis infection may be of value in understanding chronic gastrointestinal illness of unknown etiology.

New insights on classification, identification, and clinical relevance of Blastocystis spp

SUMMARY

Blastocystis is an unusual enteric protozoan parasite of humans and many animals. It has a worldwide distribution and is often the most commonly isolated organism in parasitological surveys. The parasite has been described since the early 1900s, but only in the last decade or so have there been significant advances in our understanding of Blastocystis biology. However, the pleomorphic nature of the parasite and the lack of standardization in techniques have led to confusion and, in some cases, misinterpretation of data. This has hindered laboratory diagnosis and efforts to understand its mode of reproduction, life cycle, prevalence, and pathogenesis. Accumulating epidemiological, in vivo, and in vitro data strongly suggest that Blastocystis is a pathogen. Many genotypes exist in nature, and recent observations indicate that humans are, in reality, hosts to numerous zoonotic genotypes. Such genetic diversity has led to a suggestion that previously conflicting observations on the pathogenesis of Blastocystis are due to pathogenic and nonpathogenic genotypes. Recent epidemiological, animal infection, and in vitro host-Blastocystis interaction studies suggest that this may indeed be the case. This review focuses on such recent advances and also provides updates on laboratory and clinical aspects of Blastocystis spp.

Phenotypic and genotypic characterisation of Blastocystis hominis isolates implicates subtype 3 as a subtype with pathogenic potential

Despite frequent reports on the presence of Blastocystis hominis in human intestinal tract, its pathogenicity remains a matter of intense debate. These discrepancies may be due to the varying pathogenic potential or virulence of the isolates studied. The present study represents the first to investigate both phenotypic and genotypic characteristics of B. hominis obtained from symptomatic and asymptomatic individuals. Symptomatic isolates had a significantly greater size range and lower growth rate in Jones' medium than asymptomatic isolates. The parasite cells of symptomatic isolates exhibited rougher surface topography and greater binding affinity to Canavalia ensiformis (ConA) and Helix pomatia (HPA). The present study also identifies further phenotypic characteristics, which aided in differentiating the pathogenic forms from the non-pathogenic forms of B. hominis. Blastocystis subtype 3 was found to be correlated well with the disease.

Micro-eukaryotic diversity of the human distal gut microbiota: qualitative assessment using culture-dependent and -independent analysis of faeces

Molecular ecological surveys of the human gut microbiota to date have focused on the prokaryotic fraction of the community and have revealed a remarkable degree of bacterial diversity and functionality. However, there is a dearth of information on the eukaryotic composition of the microbiota, and no culture-independent sequence-based surveys of human faeces are available. Culture-independent analyses based on DNA extraction and polymerase chain reaction targeting both the total eukaryotic 18S rRNA genes and fungal internal transcribed regions (ITS), together with culture-dependent analyses of fungi, were performed on a group of healthy volunteers. Temporal analysis was also included wherever possible. Collectively, the data presented in this study indicate that eukaryotic diversity of the human gut is low, largely temporally stable and predominated by different subtypes of Blastocystis. Specific analyses of the fungal populations indicate that a disparity exists between the cultivable fraction, which is dominated by Candida sp, and culture-independent analysis, where sequences identical to members of the genera Gloeotinia/Paecilomyces and Galactomyces were most frequently retrieved from both fungal ITS profiles and subsequent clone libraries. Collectively, these results highlight the presence of unprecedented intestinal eukaryotic inhabitants whose functional roles are as yet unknown in healthy individuals. Furthermore, differences between results obtained from traditionally employed culture-based methods and those obtained from culture-independent techniques highlight similar anomalies to that encountered when first analysing the bacterial diversity of the human faecal microbiota using culture-independent surveys.

Blastocystis sp. subtype 5: a possibly zoonotic genotype

Blastocystis has a widespread distribution in a variety of animals, which is a potential source of infection for humans. Previous studies show that Blastocystis sp. subtypes 1-4, 6, and 7 were composed of isolates from humans and animals, while Blastocystis sp. subtype 5 included only pig and cattle isolates. A more recent study on the basis of the SSU rDNA sequence has showed that a single Blastocystis isolate amplified directly from the faeces of a Thai human belongs to Blastocystis sp. subtype 5, but that study failed to cultivate this isolate. We report herein two human isolates from in vitro cultures belonging to Blastocystis sp. subtype 5 and one human isolate from in vitro culture containing two distinct genotypes of Blastocystis sp. subtypes 3 and 5 using PCR amplification with seven kinds of sequence-tagged site (STS) primers. Additionally, 16 Blastocystis isolates from pigs living in the same rural area with the three humans infected Blastocystis sp. subtype 5 were also genotyped by PCR with the STS primers, and all isolates from pigs and humans were compared by small-subunit ribosomal RNA (SSU rRNA) restriction-fragment-length polymorphism (RFLP) analyses using two restriction endonucleases (HinfI and RsaI). The results indicated that all of the isolates from pigs showed Blastocystis sp. subtype 5 and the RFLP patterns of all of the isolates from humans except for the mixed one were identical or quite similar to those of the 16 pig isolates with both HinfI and RsaI enzymes. These findings provide additional molecular-based evidence supporting the zoonotic potential of Blastocystis sp. subtype 5. This study also showed that Blastocystis sp. subtype 3 overgrew Blastocystis sp. subtype 5 in vitro.

Terminology for Blastocystis subtypes--a consensus

Blastocystis is a ubiquitous enteric protistan parasite that has extensive genetic diversity and infects humans and many other animals. Distinct molecular methodologies developed to detect variation and obtain information about transmission patterns and clinical importance have resulted in a confusing array of terminologies for the identification and designation of Blastocystis subtypes. In this article, we propose a standardization of Blastocystis terminology to improve communication and correlate research results. Based primarily on published small-subunit ribosomal RNA gene analyses, we propose that all mammalian and avian isolates should be designated Blastocystis sp. and assigned to one of nine subtypes.