Medical Fun Facts Podcast

MFF0016: Blastocystis hominis

Blastocystis hominis is a eucaryotic parasite which may or may not be pathogenic in humans.

It’s commonly found in faeces of people who have no symptoms and has usually been regarded as a commensal microorganism and of no clinical significance. The conventional wisdom is that it reflects exposure or contact with untreated water.

In faecal specimens from patients with gastrointestinal problems, Blastocystis hominis is often an incidental finding and of no consequence.

However, there are some gastroenterologists and a growing group of alternative medicine practitioners who place great weight on finding Blastocystis hominis in stool specimens. The alternative medicine (integrative) practitioners though go further and find whole stool analysis to be useful. I will do another show on whole stool analysis another time.

One of the downsides of modern technology is that with the advent of the multiplex polymerase chain reaction or multiplex PCR, as well as real pathogens like SalmonellaCampylobacter and Shigella, targets for Blastocystis hominis and Dientamœba fragilis are included because they can be. We now see more and more people who present with gastrointestinal problems being referred to pathologists for stool examination and instead of the traditional wet preparation, concentrate and culture, a multiplex PCR is being performed because it’s cheaper and faster. This has resulted in more people receiving reports indicating the presence of Blastocystis hominis in their stool. For the alternative medicine practitioners, I’ve heard they take this to mean the presence of Blastocystis hominis as significant even in the absence of symptoms like severe diarrhoea, nausea, colic, bloating, excessive flatus (farting), loss of appetite and fatigue. To confer significance in the absence of symptoms and then to offer so-called ‘natural’ remedies is farcical.

Much more research is required to discern just which strains of Blastocystis hominis may be important to human pathology and more work is needed to discourage the use of whole stool analysis which offers no real value and costs patients huge sums of money.

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