Abstract:Blastocystis is a common parasite of the human large intestine but has an uncertain role in disease. In this review, we appraise the published evidence addressing this and its weaknesses. Genetic diversity studies have led to the identification of numerous subtypes within the genus Blastocystis and, recently, methods for studying variation within subtypes have been developed, with implications for our understanding of host specificity. The geographic distribution of subtypes is summarised and the impact this may have on investigations into the role of the organism in disease is discussed. Finally, we describe the organelle and nuclear genome characteristics and look to future developments in the field.

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The development and integration of DNA-based methods in research and clinical microbiology laboratories have enabled standardised and comprehensive detection and differentiation of the microbes colonising our guts. For instance, the single-celled parasites Blastocystis and Dientamoeba appear to be much more common than previously thought, especially so in healthy individuals. While increasing evidence appears to suggest limited pathogenicity of these parasites, next-generation-sequencing-based studies have helped us to appreciate links between parasite colonisation and certain host phenotypical characteristics and gut microbial profiles. The fundamental question remains as to whether such parasites are merely indicators or active manipulators of gut microbiota structure and function. In this article, we collate existing evidence that these parasites are, at minimum, indicators of intestinal microbiota structure.

Blastocystis is a genetically diverse intestinal protist colonising both human and non-human hosts. By 2013, 17 subtypes had been acknowledged. Since then, nine more subtypes have been proposed. We argue that several recently proposed subtypes are invalid. We also revisit recommendations regarding the requirements for annotating sequences as new subtypes.

Blastocystis is a common single-celled intestinal parasitic genus, comprising several subtypes. Here, we screened data obtained by metagenomic analysis of faecal DNA for Blastocystis by searching for subtype-specific genes in coabundance gene groups, which are groups of genes that covary across a selection of 316 human faecal samples, hence representing genes originating from a single subtype. The 316 faecal samples were from 236 healthy individuals, 13 patients with Crohn's disease (CD) and 67 patients with ulcerative colitis (UC). The prevalence of Blastocystis was 20.3% in the healthy individuals and 14.9% in patients with UC. Meanwhile, Blastocystis was absent in patients with CD. Individuals with intestinal microbiota dominated by Bacteroides were much less prone to having Blastocystis-positive stool (Matthew's correlation coefficient = -0.25, P < 0.0001) than individuals with Ruminococcus- and Prevotella-driven enterotypes. This is the first study to investigate the relationship between Blastocystis and communities of gut bacteria using a metagenomics approach. The study serves as an example of how it is possible to retrospectively investigate microbial eukaryotic communities in the gut using metagenomic datasets targeting the bacterial component of the intestinal microbiome and the interplay between these microbial communities.

Blastocystis SSU-rDNA sequence data from 317 captive and free-living non-human primates (NHPs) representing 30 genera of apes, Old and New World (OW and NW) monkeys and prosimians were analysed to investigate subtype (ST) and allele distribution among hosts. Excluding 20 mixed ST infections, 27% of the sequences belonged to ST1, 22% to ST2, 34% to ST3, 1% to ST4, 4% to ST5, 11% to ST8, <1% to ST13 and 1% to ST15. The study confirmed cryptic host specificity of ST1 and ST3; conversely, considerable overlap in ST2 alleles exists among humans and NHPs. Subtype distribution in humans and NHPs differs mainly in that ST4 is rarely reported in NHPs while ST5 and ST8 are both unusual in humans. This may be due to host specificity and/or the apparent geographically restricted range of some subtypes. While the distribution of ST1, ST2 and ST3 was independent of NHP group or geographical association, ST5 was seen only in apes and OW monkeys and ST8 primarily in arboreal NHPs and only in species native to Asia or South America.

Background Maternal obesity is associated with adverse pregnancy outcomes. Probiotic supplementation during pregnancy may have positive effects on blood glucose, gestational weight gain (GWG), and the risk of gestational diabetes mellitus [GDM and glycated hemoglobin (HbA1c)]. Objectives This feasibility study involved a daily probiotic intervention in obese pregnant women from the early second trimester until delivery. The primary aim was to investigate the effect on GWG and maternal glucose homeostasis (GDM and HbA1c). Secondary aims were the effect on infant birth weight, maternal gut microbiota, and other pregnancy outcomes. Methods We carried out a randomized double-blinded placebo-controlled study in 50 obese pregnant women. Participants were randomly allocated (1:1) to multistrain probiotic (4 capsules of Vivomixx®; total of 450 billion CFU/d) or placebo at 14–20 weeks of gestation until delivery. Participants were followed with 2 predelivery visits at gestational week 27–30 and 36–37 and with 1 postdelivery visit. All visits included blood and fecal sampling. An oral-glucose-tolerance test was performed at inclusion and gestational week 27–30. Results Forty-nine participants completed the study. Thirty-eight participants took &gt;80% of the capsules (n = 21), placebo (n = 17). There was no significant difference in GWG, GDM, HbA1c concentrations, and infant birth weight between groups. Fecal microbiota analyses showed an overall increase in α-diversity over time in the probiotic group only (P = 0.016). Conclusions Administration of probiotics during pregnancy is feasible in obese women and the women were willing to participate in additional study visits and collection of fecal samples during pregnancy. Multistrain probiotic can modulate the gut microbiota in obese women during pregnancy. A larger study population is needed to uncover pregnancy effects after probiotic supplementation. This trial was registered at clincaltrials.gov as NCT02508844.

Background Taenia solium and Taenia saginata are zoonotic parasites of public health importance. Data on their occurrence in humans and animals in western Europe are incomplete and fragmented. In this study, we aimed to update the current knowledge on the epidemiology of these parasites in this region.MethodsWe conducted a systematic review of scientific and grey literature published from 1990 to 2015 on the epidemiology of T. saginata and T. solium in humans and animals. Additionally, data about disease occurrence were actively sought by contacting local experts in the different countries.ResultsTaeniosis cases were found in twelve out of eighteen countries in western Europe. No cases were identified in Iceland, Ireland, Luxembourg, Norway, Sweden and Switzerland. For Denmark, Netherlands, Portugal, Slovenia, Spain and the UK, annual taeniosis cases were reported and the number of detected cases per year ranged between 1 and 114. Detected prevalences ranged from 0.05 to 0.27%, whereas estimated prevalences ranged from 0.02 to 0.67%. Most taeniosis cases were reported as Taenia spp. or T. saginata, although T. solium was reported in Denmark, France, Italy, Spain, Slovenia, Portugal and the UK. Human cysticercosis cases were reported in all western European countries except for Iceland, with the highest number originating from Portugal and Spain. Most human cysticercosis cases were suspected to have acquired the infection outside western Europe. Cases of T. solium in pigs were found in Austria and Portugal, but only the two cases from Portugal were confirmed with molecular methods. Germany, Spain and Slovenia reported porcine cysticercosis, but made no Taenia species distinction. Bovine cysticercosis was detected in all countries except for Iceland, with a prevalence based on meat inspection of 0.0002–7.82%.ConclusionsDetection and reporting of taeniosis in western Europe should be improved. The existence of T. solium tapeworm carriers, of suspected autochthonous cases of human cysticercosis and the lack of confirmation of porcine cysticercosis cases deserve further attention. Suspected cases of T. solium in pigs should be confirmed by molecular methods. Both taeniosis and human cysticercosis should be notifiable and surveillance in animals should be improved.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-2280-8) contains supplementary material, which is available to authorized users.