BackgroundIntestinal protozoan parasites are major contributors to the global burden of gastrointestinal disease causing significant socioeconomic consequences. Children living in resource-poor settings with restricted access to water and sanitary services are particularly at risk of these infections.MethodsA prospective, community-based, cross-sectional survey was conducted in Paraná (southern Brazil) between May 2015 and May 2016. A total of 766 stool samples were individually collected from volunteers (male/female ratio: 0.99; age range: 0–76 years) and used for investigating the presence of intestinal helminth and protozoan species by routine microscopic procedures including the Kato-Katz and modified Ritchie concentration methods and the Ziehl-Neelsen stain technique. Quantitative real-time PCR confirmed microscopy-positive samples for Giardia duodenalis and the assemblages and sub-assemblages determined by multilocus sequence-based genotyping of the glutamate dehydrogenase (gdh) and β-giardin (bg) genes of the parasite. Identification of Blastocystis subtypes was carried out by amplification and sequencing of a partial fragment of the small-subunit ribosomal RNA gene (SSU rDNA) of this heterokont microorganism.ResultsOverall, 46.1% (353/766) of the participants were infected/colonised by at least one intestinal parasite/commensal species. Protozoan and helminth species were detected in 42.7% and 10.1% of the surveyed population, respectively. Blastocystis sp. (28.2%), Endolimax nana (14.9%), and Giardia duodenalis (11.0%) were the most prevalent species found among protozoans and Ascaris lumbricoides (5.0%), Trichuris trichiura (4.6%) and hookworms (1.0%) among helminths. A total of 38 G. duodenalis-positive samples were genotyped at gdh and bg markers, revealing the presence of the sub-assemblages AII (47.4%), AII/AIII (2.6%), BIII (5.3%), BIV (26.3%) and BIII/BIV (13.1%). Two samples (5.3%) were only identified as assemblage B. AII was predominantly found in females aged 5–9 years and was associated with a higher likelihood of reporting gastrointestinal symptoms. A total of 102 Blastocystis-positive samples were successfully subtyped at the SSU rRNA gene revealing the presence of ST1 (36.3%), ST2 (15.7%), ST3 (41.2%), ST4 (2.9%), ST6 (1.0%) and ST8 (2.9%).ConclusionsData presented here indicate that enteric parasites still represent a pressing health concern in Paraná, Brazil, probably due to sub-optimal water, sanitation and hygiene conditions. A mostly anthroponotic origin is suspected for G. duodenalis and Blastocystis sp. infections.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3054-7) contains supplementary material, which is available to authorized users.

Human populations living in the surrounding urban areas of large Brazilian cities have increased vulnerability to intestinal parasites. However, the epidemiological scenario of soil-transmitted helminths (STH) in Curitiba, Paraná’s main city, remains largely unknown. To bridge this gap of knowledge, this study aims to determine the prevalence of intestinal parasites and to investigate potential transmission pathways of the most prevalent species detected. We conducted a cross-sectional epidemiological study between July and September 2014 among schoolchildren in urban and peri-urban (deprived) areas of the municipality of Campo do Tenente, Curitiba. A total of 549 stool samples were used for coproparasitological diagnosis. Microscopy-positive samples of the most common species found were re-assessed by PCR and sequencing methods at the small subunit rRNA gene. Prevalence of infection by any given enteroparasite was 24.8%, but soil-transmitted helminths were only detected in 3.5% of the examined samples. Frequency of protozoan infections reached 90% and 97.8% in single and multiple infections, respectively. Blastocystis sp. (38.9%) was the most frequently species found in the surveyed schoolchildren population. A total of 41 Blastocystis-positive samples were unambiguously typed as ST1 (36.4%), ST2 (21.2%), ST3 (39.4%), and ST1 + ST3 mixed infection (3.0%). These results indicate that Blastocystis transmission is primarily anthroponotic in origin. This data highlights the importance of maintaining the anthelminthic control programs currently in place and of improving sanitary disposal of human excreta in poor-resource settings.

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Three recent studies of Blastocystis epidemiology in mammalian hosts identified four novel sequences that appeared to share B. lapemi as the most similar sequence. However, full-length ssu rRNA gene sequences were not available to confirm the validity of these new subtypes. In the present study, Nanopore MinION sequencing was used to obtain full-length reference sequences for each of the new subtypes. Additionally, phylogenetic analyses and pairwise distance comparisons were performed to confirm the validity of each of these new subtypes. We propose that the novel sequences described in this study should be assigned the subtype designations ST35-ST38. The full-length reference sequences of ST35-ST38 will assist in accurate sequence descriptions in future studies of Blastocystis epidemiology and subtype diversity.

The symptomatology of Blastocystis cannot be attributed to any particular subtype, although can be related to a high Blastocystis infection load. One stool sample from each of 217 schoolchildren of Vale de Sol Paranaguá Bay (Paraná, Brazil) was collected. Three milliliters of each fixed stool sample were processed applying the formalin-ether concentration technique. After obtaining the overall prevalence of intestinal parasites, quantification was carried out in Blastocystis positive samples. A total of 75/217 (34.6%) children suffered from intestinal symptoms (abdominal pain and/or persistent diarrhea), of whom 41.3% (31/75) presented moderate/heavy Blastocystis load with a statistically significant risk to present intestinal symptoms (OR 0.039 [0.006-0.15]; p<0.001) Moreover, those symptomatic schoolchildren monoparasitized only by Blastocystis (10/75, 13.3%), and those polyparasitized by Blastocystis with other non-pathogenic species (15/75, 20%) with moderate/heavy loads, also entail a statistically significant risk of intestinal symptomatology, both in monoparasitism (12%, OR 0.10 [0.004-0.63]; p=0.021) and in polyparasitism with a non-pathogenic parasite (18.6%, OR 0.059 [0.002-0.35]; p=0.001). For the first time in Brazil, using data from schoolchildren of Paranaguá Bay, we demonstrated that moderate/ heavy loads of Blastocystis could be related to intestinal symptoms.