I've tried to summarise a few facts here:
- Blastocystis is a single-celled, microbial parasitic protist colonising mainly the large intestine of man and other mammals, birds, reptiles, and other animals, even insects.
- The parasite is extremely common in humans, and possibly the most common microbial non-fungal eukaryote in the human intestine. More than one billion people may be colonised.
- Blastocystis comprises many ribosomal lineages, most or all of which are comparable to separate species; they are currently known as subtypes (ST).
- Humans are common hosts of ST1, ST2, ST3 and ST4, whereas other subtypes such as ST6, ST7 and ST8 are seen occasionally. ST5 and ST9 are very rare in humans.
- Almost all subtypes found in humans are also found in animals; however, zoonotic transmission is probably uncommon, at least for the most common subtypes (ST1—ST4).
- Most carriers do probably not experience more intestinal symptoms than the average individual.
- We do not know when to seek to eradicate Blastocystis and there are no valid treatment guidelines. The effect of metronidazole may be very limited.
- ST3 is probably the most common subtype in humans.
- ST4 may be more much more common in Europe than outside Europe.
- ST4 has been seen frequently in patients with different types of diarrhoea or other intestinal problems, but appears uncommon in healthy individuals.
- Blastocystis is best detected by (real-time) PCR and culture; conventional parasitological techniques have generally poor sensitivity.
· Ongoing epidemiological studies seek to analyse subtype distributions in various cohorts, e.g. IBS patients and the background population. We also continuously explore the genetic variation and host specificity of Blastocystis. Genome studies seek to unravel virulence genes that may be involved in pathogenesis, but only the genome for ST7 has been sequenced so far.