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
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Blastocystis colonizes the large intestine and divides by binary fission. In vitro, Blastocystis can adhere to intestinal
mucin and secrete cysteine proteases that contribute to pathogenesis through degradation of secretory IgA, Rho/
ROCK-mediated tight-junction compromise, NF-κB-mediated secretion of inflammatory cytokines, and host cell
apoptosis. It is currently unknown whether this occurs in vivo. Most gut microbiota studies that include Blastocystis
report that Blastocystis is a common constituent of the healthy gut microbiota and is associated with higher bacterial
richness, and that long-term asymptomatic carriage is common. In contrast, a couple of recent studies have
suggested that Blastocystis decreases beneficial gut bacteria, leading to a dysbiotic state. Such discrepant observations
have led to confusion on the clinical relevance of the parasite. Blastocystis is relatively rare in patients with
inflammatory bowel disease, and its role in irritable bowel syndrome is still controversial.
KEY FACTS:
Blastocystis from mammals and birds
can be classified into at least 17 subtypes
(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 specificity
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
previous species were invalid or
represented multiple very distinct entities.
DISEASE FACTS:
Despite more than 1 billion carriers
worldwide, the public health significance
remains unknown.
Blastocystis has been found more commonly
in the gastrointestinal tract of
healthy individuals.
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
*Correspondence:
run@ssi.dk (C.R. Stensvold).
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Trends in Parasitology, March 2020, Vol. 36, No. 3 © 2020 Elsevier Ltd. All rights reserved. https://doi.org/10.1016/j.pt.2019.12.008 315
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Resources
www.pubmlst.org/blastocystis
Literature
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