Introduction
Blastocystis, a protist commonly found in the human gastrointestinal tract, is one of the most prevalent eukaryotic microorganisms globally1. It exhibits significant genetic diversity, with at least 44 subtypes (STs) identified to date based on sequence analyses of the small subunit ribosomal RNA (SSU rRNA) gene2,3. Among these, ST1-ST10, ST12, ST14, ST16, ST23, ST35, and ST41 have been reported from humans, with ST1 to ST4 being the most frequently identified4,5. The interaction of Blastocystis with the gut microbiota and the host immune system has been linked to a range of clinical outcomes, highlighting its potential relevance to human health6.
Blastocystis is distributed worldwide, with varying occurrence rates across different regions. It has been reported globally, with variations likely influenced by differences in sanitation and hygiene practices7. Blastocystis is found to be present in both healthy individuals and those experiencing gastrointestinal symptoms. Some studies have reported associations between symptoms such as diarrhea, abdominal pain, bloating, and the presence of Blastocystis8. However, these associations are inconsistent across studies, and the public health significance of Blastocystis remains uncertain, primarily due to conflicting evidence regarding its role in health and disease.
The clinical significance of Blastocystis has been a topic of ongoing debate. Historically considered a parasitic organism, some studies have questioned whether certain subtypes or host interactions might contribute to health outcomes in specific contexts9. The genetic diversity of Blastocystis adds complexity, with some subtypes being more frequently detected in symptomatic individuals, while others are commonly found in asymptomatic populations. The interplay between Blastocystis, the host immune response, and the gut microbiota is believed to play a critical role in determining its impact on human health10.
The existing literature presents diverse perspectives on Blastocystis. Some studies suggest that Blastocystis presence may be associated with beneficial changes in the gut microbiota, such as increased bacterial diversity and anti-inflammatory responses8. Conversely, some studies report that Blastocystis may be associated with reduced beneficial bacteria and an altered gut microbiome composition11. Given the conflicting evidence regarding the pathogenicity of Blastocystis, a comprehensive scoping review is warranted to systematically map the existing evidence. This review will synthesize original research studies on human subjects, focusing on the association between Blastocystis presence and various clinical outcomes.
Objectives
The primary objective of this scoping review is to systematically map the existing evidence on Blastocystis presence and clinical outcomes in humans. This review will help clarify the current state of knowledge, identify research gaps, and provide a foundation for future studies that can further explore this relationship. The following research questions will be assessed:
1. What evidence exists on the relationship between Blastocystis occurrence and human clinical outcomes?
2. What evidence exists regarding the diagnostic methods used for Blastocystis detection, and their performance and accuracy?
3. What evidence is available on the treatment and management options for Blastocystis?
Methods
This scoping review will be conducted and reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) extension for scoping reviews (PRISMA-ScR)12.
Literature searches
Systematic searches for relevant published studies will be conducted in PubMed, EMBASE, Web of Science, and the Cochrane Library. An experienced methodologist will develop and validate search strategies to ensure maximum sensitivity. Searches will be performed without time restrictions, and the date of the search, search strategy, and number of search results will be documented for each database.
Selection of studies
The selection process will involve two stages: screening and eligibility assessment. Titles and abstracts will be screened by two independent reviewers to identify potentially relevant studies, using Rayyan. Full-text articles of studies deemed relevant will be retrieved and assessed for eligibility based on predefined criteria, by two reviewers. Disagreements will be resolved through discussion or by consulting a third reviewer. Screening results and reasons for exclusion will be documented in PRISMA flowcharts.
Eligibility criteria
To be included in this scoping review, studies must involve human participants with confirmed (or, for the diagnostic question, suspected) Blastocystis infection. To be a confirmed case, the infection must be diagnosed using reliable methods such as direct microscopy, culture, conventional and qPCR, or next-generation sequencing (NGS). Studies that primarily focus on other parasitic infections, where Blastocystis is not the main focus, will be excluded.
Studies that include both symptomatic and asymptomatic individuals with Blastocystis infection will be eligible, as this should assist in providing a comprehensive understanding of the organism’s potential pathogenicity and its association with various clinical outcomes (Table 1).
Table 1. Inclusion and exclusion criteria for each research question.
| Research Question | Population | Exposure | Comparator | Outcomes | Study Design | Exclusion criteria |
|---|
| 1 | What evidence exists
on the relationship
between Blastocystis
infection and clinical
outcomes, and
pathogenicity in
humans? | Humans of all ages | Blastocystis infection | No Blastocystis
infection | All reported clinical
outcomes (e.g.,
gastrointestinal/extra-
intestinal symptoms,
pathogenicity etc.) | Cross-sectional,
cohort studies,
case-control studies,
prevalence studies,
systematic reviews. | Study Type: Editorials,
letters, commentaries,
conference abstracts,
case series, case reports,
clinical guidelines,
narrative reviews (though
reference lists will be
screened), and non-peer-
reviewed works (e.g.,
theses, preprints).
Subject: Animal studies
or research conducted
solely in non-human
settings (e.g., laboratory/
animal models).
Confirmation: Studies
where Blastocystis
infection is neither
confirmed nor suspected.
Results: Studies reporting
combined treatment
outcomes without
Blastocystis-specific
results
Focus: Studies where
Blastocystis is not the
main focus, including
those primarily
addressing other
parasitic infections or
treatments not targeting
Blastocystis specifically.
Language: Except
English, Greek, Spanish,
German, French,
Norwegian, Danish,
Russian, and Turkish. |
| Research Question | Population | Index Test | Reference Test | Outcomes | Study Design |
|---|
| 2 | What evidence
exists regarding the
diagnostic methods
used for Blastocystis
diagnosis, and their
performance? | Humans of all
ages suspected of
Blastocystis infection | Diagnostic methods
(e.g., microscopy,
culture, molecular
diagnostics) | Any reference
standard or
another diagnostic
method | All reported test
accuracy outcomes. | Diagnostic accuracy
studies, clinical trials,
systematic reviews. |
| Research Question | Population | Intervention | Comparator | Outcomes | Study Design |
|---|
| 3 | What evidence is
available on the
treatment options for
Blastocystis infection,
and how effective are
these interventions
in managing the
infection and
associated symptoms? | Humans of all ages
with confirmed
Blastocystis infection | Any treatment for
Blastocystis | No treatment,
placebo, or
alternative
strategies | All reported outcomes
(e.g. eradication of
Blastocystis, symptom
resolution etc.) | Clinical trials, cross-
sectional, cohort
studies, case-control
studies, systematic
reviews. |
Studies published in all languages spoken by the panel members will be considered (English, Greek, Spanish, German, French, Norwegian, Danish, Russian, and Turkish), in order to maximize data capture.
Eligible study types include randomized and non-randomized trials, cohort studies, case-control, systematic reviews, and cross-sectional studies (with or without a control group). Editorials, letters, commentaries, conference abstracts, case series, case reports, clinical guidelines, narrative reviews, and non-peer-reviewed work (e.g. theses), will be excluded. Narrative review articles will not be included, but their reference lists will be explored for further data sources (Table 1).
No date limit will be used for the inclusion criteria, in order to provide a full evidence map on this topic.
Data extraction
Data from included studies will be charted using a standardized data extraction form. The form will be piloted to ensure consistency and reliability. Data extraction will be performed independently by two reviewers, with cross-checking to resolve discrepancies. Additional data or clarifications will be sought from study authors when required.
Data items
The data items to be extracted will include:
Study Characteristics: Author, year of publication, study type, design, setting, and geographical location.
Population Details: Number of participants, age, gender
Details of Blastocystis Infection: Detection methods used, subtype identification, presence or absence of symptoms.
Clinical Outcomes: All reported symptoms (including gastrointestinal, dermatologic etc. symptoms), associations with Blastocystis subtypes (if reported), any given treatment and treatment outcome, and any other clinically relevant outcome
Subgroups: studies will be presented in subgroups based on study design and patient population.
Results
The results section will describe the evidence of the relationship between Blastocystis infection and clinical outcomes, variations in outcomes based on diagnostic methods, and the pathogenicity of specific Blastocystis subtypes. Identified and included studies will be presented in both tabular and graphical forms, offering a complete evidence map on this topic. Research gaps will also be identified, and recommendations for future studies will be provided.
Critical appraisal of individual sources of evidence
As critical appraisal is not a mandatory step in scoping reviews, it is not planned to be conducted.
Discussion and conclusions
The findings of this scoping review will provide a comprehensive synthesis of the current evidence on Blastocystis's potential associations with clinical outcomes. Despite its high prevalence and global distribution, Blastocystis remains poorly understood, with conflicting perspectives regarding its clinical relevance13.
In conclusion, this scoping review aims to serve as a foundational resource for researchers and clinicians, guiding the design of targeted studies and providing a robust evidence base for Blastocystis research.
Ethics and consent
Ethics and consent were not required.
Data availability statement
No data are associated with this article
Faculty Opinions recommendedReferences
- 1.
Stensvold CR:
Thinking Blastocystis out of the box.
Trends Parasitol.
2012; 28(8): 305. PubMed Abstract
| Publisher Full Text
- 2.
Maloney JG, Molokin A, Seguí R, et al.:
Identification and molecular characterization of four new Blastocystis subtypes designated ST35-ST38.
Microorganisms.
2023; 11(1): 46. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 3.
Koehler AV, Herath HMPD, Hall RS, et al.:
Marked genetic diversity within Blastocystis in Australian wildlife revealed using a next generation sequencing-phylogenetic approach.
Int J Parasitol Parasites Wildl.
2024; 23: 100902. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 4.
Jinatham V, Yowang A, Stensvold CR, et al.:
Blastocystis colonization and associations with population parameters in Thai adults.
PLoS Negl Trop Dis.
2024; 18(7): e0012292. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 5.
Hernández-Castro C, Maloney JG, Agudelo-López SP, et al.:
Identification and validation of novel Blastocystis subtype ST41 in a Colombian patient undergoing colorectal cancer screening.
J Eukaryot Microbiol.
2023; 70(5): e12978. PubMed Abstract
| Publisher Full Text
- 6.
Deng L, Wojciech L, Gascoigne NRJ, et al.:
New insights into the interactions between Blastocystis, the gut microbiota, and host immunity.
PLoS Pathog.
2021; 17(2): e1009253. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 7.
El Safadi D, Gaayeb L, Meloni D, et al.:
Children of senegal river basin show the highest prevalence of Blastocystis sp. ever observed worldwide.
BMC Infect Dis.
2014; 14: 164. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 8.
Boorom KF, Smith H, Nimri L, et al.:
Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection.
Parasit Vectors.
2008; 1(1): 40. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 9.
Ajjampur SSR, Tan KSW:
Pathogenic mechanisms in Blastocystis spp. — Interpreting results from in vitro and in vivo studies.
Parasitol Int.
2016; 65(6 Pt B): 772–9. PubMed Abstract
| Publisher Full Text
- 10.
Aykur M, Malatyalı E, Demirel F, et al.:
Blastocystis: a mysterious member of the gut microbiome.
Microorganisms.
2024; 12(3): 461. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 11.
Yason JA, Liang YR, Png CW, et al.:
Interactions between a pathogenic Blastocystis subtype and gut microbiota: in vitro and in vivo studies.
Microbiome.
2019; 7(1): 30. PubMed Abstract
| Publisher Full Text
| Free Full Text
- 12.
Tricco AC, Lillie E, Zarin W, et al.:
PRISMA extension for Scoping Reviews (PRISMA-ScR): checklist and explanation.
Ann Intern Med.
2018; 169(7): 467–73. PubMed Abstract
| Publisher Full Text
- 13.
Tsaousis AD, Gentekaki E, Stensvold CR:
Advancing research on Blastocystis through a One Health approach [version 1; peer review: 3 approved].
Open Res Eur.
2024; 4: 145. PubMed Abstract
| Publisher Full Text
| Free Full Text
