Variable geographic distribution of Blastocystis subtypes and its potential implications

Abstract

Blastocystis is a common intestinal micro-eukaryote found in both humans and non-human hosts and known to be genetically very diverse. It has been divided into numerous subtypes (STs), nine of which have been identified in humans to date. Surveys of ST prevalence have started to emerge over the past few years but to date no data are available for any African country except Egypt and Tanzania. In this study, we determined the prevalence of Blastocystis STs in populations from Libya, Liberia and Nigeria, as well as expanding the dataset available for the UK. A total of 356 Blastocystis STs were identified in this study, 271 from the UK, 38 from Libya, 25 from Liberia and 22 from Nigeria. SSU rRNA gene sequences revealed the presence of eight of the nine STs known from humans but at varying frequencies between countries. ST1 was the most common ST in Libya and Nigeria whereas ST3 showed the highest frequency in the other two countries, as indeed is the case in most populations around the world. ST4 was absent in Libya and ST2 in Nigeria, while no ST5, ST6, ST8 or ST9 infections were detected in any of the three African populations. The picture emerging from this and other surveys suggests that there is significant variation in ST prevalence between populations. Some of the possible reasons for and implications of this diversity are discussed.

Recent Developments in Blastocystis Research

“…In Pakistan (Yakoob et al, 2010) and Egypt (Fouad et al, 2011) significant differences in subtype distribution were found, with ST1 being much more common in IBS patients than controls. A study in the UK found ST4 to be more common and ST1 less so in patients from IBS clinics than in other diagnostic laboratory samples, but not reaching statistical significance (Alfellani et al, 2013). Again, there was a difference in methodology (STS vs. sequencing) as well as many other variables, not the least of which is geography and the presence of ST4, so the potential relationship needs further investigation.…”

“…Together, these make up around 90% of all human Blastocystis in surveys that involve subtyping (Alfellani et al, 2013). These will be discussed further below.…”

“…This subtype is very common in Europe (often the second most common ST found after ST3), but apparently absent in Egypt, Libya, Iran, Nepal, the Philippines, Thailand, Malaysia and Brazil, and rare in many other countries (see summary in Alfellani et al, 2013). Again, there may be some link to the method used (STS in Asia) but not in all countries as sequencing was used in the studies from Libya and Brazil, for example.…”

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

“…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, 2013;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, …”

Molecular Identification and Subtype Analysis of Blastocystis

“…A subtype such as ST4 is common only in Europeans, while subtypes 1-3 are common in humans all over the world (Alfellani et al, 2013b). On the other hand, subtypes other than those belonging to ST1-ST4 appear to be relatively rare in humans (Alfellani et al, 2013b). ST3 is common in both human and nonhuman primates; however, ST3 allele analysis has demonstrated that ST3 strains found in humans and non-human primates are different (Stensvold et al, 2012b).…”