Trends in Parasitology | Parasite of the Month

Blastocystis
Christen Rune Stensvold,1,* Kevin S.W. Tan,2 and C. Graham Clark3
1
Statens Serum Institut, Copenhagen, Denmark
2
National University of Singapore, Singapore
3
London School of Hygiene and Tropical Medicine, London, UK

KEY FACTS:
Blastocystis from mammals and birds
can be classified into at least 17 sub-
types (STs) currently, based on small
subunit (SSU) rRNA genes. STs are as
divergent as species or even genera.

Humans can host ST1–9 and 12; more

than 90% of human Blastocystis strains
belong to ST1–4.

Reservoir hosts have been identified for all

subtypes except ST9; cryptic host speci-
ficity exists for at least some of them.

Two genomes: a nuclear genome of

12.9–18.8 Mb (depending on ST)
encoding 5713–6544 proteins, and a
mitochondrial genome of 27.7–29.3 kb.

Blastocystis can be cultured easily in

Jones’ and other media with fecal
bacteria. A genetic manipulation method
for ST7 has been described recently.

Subtype nomenclature was introduced

when it became clear that the names of
Trends in Parasitology previous species were invalid or
represented multiple very distinct entities.

Blastocystis colonizes the large intestine and divides by binary fission. In vitro, Blastocystis can adhere to intestinal DISEASE FACTS:
mucin and secrete cysteine proteases that contribute to pathogenesis through degradation of secretory IgA, Rho/ Despite more than 1 billion carriers
ROCK-mediated tight-junction compromise, NF-κB-mediated secretion of inflammatory cytokines, and host cell worldwide, the public health significance
apoptosis. It is currently unknown whether this occurs in vivo. Most gut microbiota studies that include Blastocystis remains unknown.
report that Blastocystis is a common constituent of the healthy gut microbiota and is associated with higher bac-
terial richness, and that long-term asymptomatic carriage is common. In contrast, a couple of recent studies have Blastocystis has been found more com-
suggested that Blastocystis decreases beneficial gut bacteria, leading to a dysbiotic state. Such discrepant obser- monly in the gastrointestinal tract of
vations have led to confusion on the clinical relevance of the parasite. Blastocystis is relatively rare in patients with healthy individuals.
inflammatory bowel disease, and its role in irritable bowel syndrome is still controversial.
Gut bacterial diversity and richness are
mostly higher in Blastocystis-positive
individuals. ST7 has been shown to
decrease the levels of beneficial gut
bacteria such as Bifidobacterium and
Lactobacillus.

The zoonotic contribution to human

Blastocystis colonization is probably low.

TAXONOMY AND CLASSIFICATION:

KINGDOM: Sar
PHYLUM: Stramenopiles
CLASS: Bigyra
ORDER: Opalinata
FAMILY: Blastocystidae
GENUS: Blastocystis
SPECIES: Currently not applicable

Trends in Parasitology
*Correspondence:
run@ssi.dk (C.R. Stensvold).

Trends in Parasitology, Month 2020, Vol. xx, No. xx © 2020 Elsevier Ltd. All rights reserved. https://doi.org/10.1016/j.pt.2019.12.008 1
Trends in Parasitology | Parasite of the Month
Resources
www.pubmlst.org/blastocystis

Literature
1. Stensvold, C.R. et al. (2007) Terminology for Blastocystis subtypes – a consensus. Trends Parasitol. 23, 93–96
2. Adl, S.M. et al. (2019) Revisions to the classification, nomenclature, and diversity of eukaryotes. J. Eukaryot. Microbiol. 66, 4–119
3. Clark, C.G. et al. (2013) Recent developments in Blastocystis research. Adv. Parasitol. 82, 1–32
4. Tito, R.Y. et al. (2019) Population-level analysis of Blastocystis subtypes prevalence and variation in the human gut microbiota. Gut 68, 1180–1189
5. Denoeud, F. et al. (2011) Genome sequence of the stramenopile Blastocystis, a human anaerobic parasite. Genome Biol. 12, R29
6. Gentekaki, E. et al. (2017) Extreme genome diversity in the hyper-prevalent parasitic eukaryote Blastocystis. PLoS Biol. 15, e2003769
7. Silberman, J.D. et al. (1996) Human parasite finds taxonomic home. Nature 380, 398
8. Li, F.J. et al. (2019) Successful genetic transfection of the colonic protistan parasite Blastocystis for reliable expression of ectopic genes. Sci. Rep. 9, 3159
9. Yason, J.A. et al. (2019) Interactions between a pathogenic Blastocystis subtype and gut microbiota: in vitro and in vivo studies. Microbiome 7, 30
10. Beghini, F. et al. (2017) Large-scale comparative metagenomics of Blastocystis, a common member of the human gut microbiome. ISME J. 11, 2848–2863

2 Trends in Parasitology, Month 2020, Vol. xx, No. xx © 2020 Elsevier Ltd. All rights reserved. https://doi.org/10.1016/j.pt.2019.12.008