Mapping Blastocystis epidemiology and diagnostics across Europe: A One Health survey of professional practice, perceptions and unmet needs

Blastocystis is one of the most prevalent intestinal protists in humans and animals, yet its clinical significance remains unresolved, and its diagnosis is poorly standardised. We aimed to map professional practice, perceptions, and unmet needs in Blastocystis epidemiology and diagnostics across Europe. Within the European Cooperation in Science and Technology (COST) Action CA21105, Working Group 1 conducted a multinational cross-sectional survey using a dedicated structured online questionnaire distributed through national representatives and European professional networks across COST member countries, and responses on institutional profiles, diagnostic and subtyping workflows, perceived clinical relevance, and treatment were analysed using Pearson chi-square tests. A total of 439 fully completed, valid questionnaires from 38 countries were evaluated. Human-derived stool samples predominated (75.3%). Microscopy remained the principal screening method (61.6%), whereas only 16.9% used molecular methods alone, and 75.0% performed no subtyping. Subtyping was associated with institution type and research purpose (p < 0.001): universities and epidemiological laboratories drove barcoding/Sanger sequencing, whereas health institutions most often did not subtype. Reporting to clinicians was inconsistent (20.5% never reported). Most clinicians (96.2%) linked Blastocystis to gastrointestinal symptoms, and metronidazole was the predominant treatment choice (57.8%) despite inconsistent efficacy. Respondents endorsed standardisation and data-sharing, citing the lack of guidelines and inter-group communication (44.6%), as well as insufficient funding, as the principal barriers to improving practices. Overall, a marked gap separates near-universal professional conviction in the clinical relevance of Blastocystis from the diagnostic and molecular capacity to test it; these findings provide an evidence base for uniform, One Health–oriented guidelines for Blastocystis diagnosis and surveillance across Europe.