Blastocystis identified in humans used to be referred to as "Blastocystis hominis". However, after the advanced use of nucleic acid-based tools in the 90s and 00s it became clear that
1) morphologically identical Blastocystis can be genetically extremely diverse
2) Blastocystis in humans comprises at least 9 species (or, perhaps more correctly, ribosomal lineages), 8 of which can be found in other animals as well.
This means that host origin is not a reliable indicator of organism identity.
Blastocystis appears to exhibit only moderate host specificity - at least at subtype level - , and until a more substantial sampling from various hosts has been carried out, we will have to go with "Blastocystis sp." followed by an appropriate subtype (ST) number (according to species/ribosomal lineage), e.g. "Blastocystis sp. ST3", which is one of the 4 subtypes commonly found in humans.
In order to make subtype analysis very easy, we have created a site (together with Keith Jolley, Oxford University), where a bulk of sequences can be assigned to subtype in few seconds. Single sequence entries are also possible.
To sum up: Blastocystis hominis is a misleading and currently an invalid taxon.
(Read more about this in our Blastocystis consensus paper from 2007 in Trends in Parasitology)
1) morphologically identical Blastocystis can be genetically extremely diverse
2) Blastocystis in humans comprises at least 9 species (or, perhaps more correctly, ribosomal lineages), 8 of which can be found in other animals as well.
This means that host origin is not a reliable indicator of organism identity.
Blastocystis appears to exhibit only moderate host specificity - at least at subtype level - , and until a more substantial sampling from various hosts has been carried out, we will have to go with "Blastocystis sp." followed by an appropriate subtype (ST) number (according to species/ribosomal lineage), e.g. "Blastocystis sp. ST3", which is one of the 4 subtypes commonly found in humans.
In order to make subtype analysis very easy, we have created a site (together with Keith Jolley, Oxford University), where a bulk of sequences can be assigned to subtype in few seconds. Single sequence entries are also possible.
To sum up: Blastocystis hominis is a misleading and currently an invalid taxon.
(Read more about this in our Blastocystis consensus paper from 2007 in Trends in Parasitology)
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