Elsevier

Infection, Genetics and Evolution

Volume 45, November 2016, Pages 95-97
Infection, Genetics and Evolution

Research paper
Prevalence and genetic diversity of Blastocystis in family units living in the United States

https://doi.org/10.1016/j.meegid.2016.08.018Get rights and content

Highlights

  • First PCR-based survey of Blastocystis in a US population using Blastocystis specific primers.

  • Prevalence of Blastocystis in this study is comparatively low relative to other western populations investigated to date.

  • Blastocystis subtype diversity is largely consistent with that previously reported from studies of European populations.

  • Our data indicates that human-human transmission is unlikely to have occurred within families studied here.

Abstract

The human gut is host to a diversity of microorganisms including the single-celled microbial eukaryote Blastocystis. Although Blastocystis has a global distribution, there is dearth of information relating to its prevalence and diversity in many human populations. The mode of Blastocystis transmission to humans is also insufficiently characterised, however, it is speculated to vary between different populations. Here we investigated the incidence and genetic diversity of Blastocystis in a US population and also the possibility of Blastocystis human-human transmission between healthy individuals using family units (N = 50) living in Boulder, Colorado as our sample-set. Ten of the 139 (~ 7%) individuals in our dataset were positive for Blastocystis, nine of whom were adults and one individual belonging to the children/adolescents group. All positive cases were present in different family units. A number of different Blastocystis subtypes (species) were detected with no evidence of mixed infections. The prevalence of Blastocystis in this subset of the US population is comparatively low relative to other industrialised populations investigated to date; however, subtype diversity was largely consistent with that previously reported in studies of European populations. The distribution of Blastocystis within family units indicates that human-human transmission is unlikely to have occurred within families that participated in this study. It is not unexpected that given the world-wide variation in human living conditions and lifestyles between different populations, both the prevalence of Blastocystis and its mode of transmission to humans may vary considerably.

Introduction

Blastocystis is a single-celled microbial eukaryote that is commonly found in the intestinal tract of a diverse range of non-mammalian and mammalian hosts including humans (Alfellani et al., 2013a, Alfellani et al., 2013b, Tan, 2008). As a consequence of the controversial and unresolved role of Blastocystis in human intestinal disease and the increased awareness of the importance of the gut microbiome (and specific components of the gut microbiome) in human health, research into Blastocystis has greatly increased (Andersen and Stensvold, 2016, Guinane and Cotter, 2013, Roberts et al., 2014, Scanlan, 2012, Scanlan and Stensvold, 2013, Sekirov et al., 2010). Over the past few years the application of sensitive molecular PCR based techniques has also facilitated a better appreciation of the prevalence of Blastocystis in human populations, however, there still remains a lack of reliable epidemiological data on the prevalence and genetic diversity of Blastocystis from many regions of the world (Alfellani et al., 2013a, Alfellani et al., 2013b) including the United States. Moreover, a number of questions relating to the basic ecology and epidemiology of Blastocystis including the mode of Blastocystis transmission to humans remain unanswered (Clark et al., 2013).

It is estimated that more than one billion people worldwide are colonised by Blastocystis (Andersen and Stensvold, 2016). However, there is considerable variation in prevalence rates between different populations; for example, recent reports have given positive prevalence rates of anywhere between ~ 24–100% for different populations living in Europe, the Middle East, India and Africa (AbuOdeh et al., 2016, Alfellani et al., 2013a, Alfellani et al., 2013b, Bart et al., 2013, El Safadi et al., 2014, Krogsgaard et al., 2015, Pandey et al., 2015, Scanlan and Stensvold, 2013, Scanlan et al., 2014). With respect to Blastocystis transmission to humans, three distinct modes of transmission have been proposed (Tan, 2008). Firstly, there is some evidence of zoonotic transmission; however, this is most likely to occur only in certain circumstances and for specific subtypes (STs), e.g. close contact with animals that are host to subtypes that can also colonise humans (Alfellani et al., 2013b, Parkar et al., 2010, Wang et al., 2014). Secondly, environmental sources such as drinking water may also be a potential source of Blastocystis (Leelayoova et al., 2008, Taamasri et al., 2000). Poor sanitation and unsuitable water treatment resulting in the consumption of contaminated water are likely to be contributory in this regard (Taamasri et al., 2000, Tan et al., 2010). Finally, direct human-to-human transmission through contact with infected individuals (directly or indirectly via contaminated food and water) has also been postulated (Anuar et al., 2013, Yoshikawa et al., 2000).

In this study, we analysed the prevalence and genetic diversity of Blastocystis in a subset of the US population and also investigated the possibility of human-to-human transmission of Blastocystis between healthy individuals using families as our sample-set. We deliberately chose families from a limited geographical area as we anticipated that, if human-human transmission of Blastocystis is possible, more of the same Blastocystis STs (alleles) would be shared within, rather than between, family groups. The use of families also facilitates investigation of specific patterns of transmission including vertical and/or horizontal transmission, for example, between mothers and children and between partners and/or children. Moreover, in addition to close human-to-human contact, family groups also possess several attributes that further the analysis of human-to-human transmission including shared environments and degree of genetic relatedness. Our sample-set also included dogs which also allowed for the investigation of dogs as carriers of Blastocystis and potential sources of transmission to humans.

Section snippets

Overview of study and participants

The aim of our study was to survey the prevalence and genetic diversity of Blastocystis in a subset of the (healthy) US population and to investigate the possible human-human transmission of Blastocystis within families. Our samples were taken from a previous study that comprised 50 family units (FUs), (adults, N = 101; mean age, 34.8 years; children/adolescents, N = 38; mean age, 4.1 years) (Song et al., 2013), see Table 1. This dataset also included dogs, which we investigated as a possible source

Results

We detected Blastocystis in 10 of the 139 (~ 7%) individuals in our dataset, see Supplementary Table 1. We found no evidence of mixed Blastocystis infections using ST-specific primers. The cohort of individuals positive for Blastocystis could be further subdivided into two groups; adults and children/adolescents, with nine and one individual(s), respectively, positive for Blastocystis. Of the adults, eight were male and one female and the positive child/adolescent sample was a two year old

Discussion

A renewed research interest in the microbial eukaryote Blastocystis has been largely driven by a greater appreciation of its genetic and phenotypic diversity, ubiquity in human and animal populations, and its potential role in both human health and disease (Andersen and Stensvold, 2016, Tan et al., 2010). Currently, there is little information on Blastocystis prevalence and diversity in US populations derived from sensitive molecular methodologies. Although this is a relatively small sample-set

Conclusions

It is becoming increasingly clear that the prevalence of Blastocystis varies considerably between industrialised (and non-industrialised) populations and that source(s) of Blastocystis transmission to humans will likely vary depending on the population under study. The factors that underpin variation in prevalence are currently unknown but differences in global human living conditions, including sanitation levels, access to clean water and contact with animals that are host to Blastocystis, are

Acknowledgements

This work was funded by a Marie Curie Intra-European Fellowship to Dr Pauline Scanlan. We are grateful to Dr Christen R. Stensvold for useful comments on the manuscript.

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