Wednesday, April 3, 2013

Blastocystis and IBD

We recently published what could be seen as a pilot study on inflammatory bowel disease (IBD) and the two most common intestinal parasites, Blastocystis and Dientamoeba fragilis.

The aim of the study was to identify possible differences in the prevalence of infection with Blastocystis and D. fragilis in patients with active and inactive IBD compared to controls.

We included 100 Danish patients with IBD (42 with Crohn's Disease, 41 with ulcerative colitis and 17 with ileal pouch-anal anastomosis) and 96 controls, used state-of-the-art diagnostics for Blastocystis and D. fragilis (PCR) and we saw striking differences in prevalence. While 19% of all healthy individuals had Blastocystis, only 5% of those with IBD had Blastocystis, and of the 42 patients with Crohn's Disease, only 1 had Blastocystis. In contrast, D. fragilis was not more common in healthy individuals than in IBD patients. Also, in patients with ulcerative colitis, Blastocystis was significantly more common in patients with inactive disease compared to patients with active disease.

Absence of Blastocystis in patients with Crohn's Disease and active ulcerative colitis may be due to unfavourable conditions for colonisation and should be explored further in order to investigate whether these potentially unfavourable conditions reflect differences in the composition of the microbiota in these patients, and/or whether this has something to do with host immunity. We are currently confirming the virtual absence of Blastocystis in Crohn's patients in another study based on metagenomic analysis of faecal DNA, and it will be very interesting to analyse the differences in Blastocystis prevalence in view of potential differences in bacterial communities.

The literature on Blastocystis and IBD is relatively limited, and I plan to return, maybe later this year, with a more elaborate post on the topic.


Petersen AM, Stensvold CR, Mirsepasi H, Engberg J, Friis-Møller A, Porsbo LJ, Hammerum AM, Nordgaard-Lassen I, Nielsen HV, & Krogfelt KA (2013). Active ulcerative colitis associated with low prevalence of Blastocystis and Dientamoeba fragilis infection. Scandinavian journal of gastroenterology PMID: 23528075


  1. This is quite interesting. I've read that a large number of B. hominus can infect mouse models (titer dependent). I haven't found any studies that use the chemically induced colitis mouse model in combination with B. hominus to determine if Blastocystis knocks down or exacerbates the auto-immune response in mice. It would be interesting to know if supplements of Blastocystis could be used to ameliorate symptoms (like Bacteroides uniformes usage to treat metabolic syndrome symptoms).

    IBS seems to be associated with the opposite trend-high B. hominis. Do you have any guesses about why this might be the case?

  2. Dear William,

    thanks for the comment.

    Yes, it is very exciting! After several years in business now, my experience is that - at least in Denmark - the lowest prevalence of Blastocystis is seen in patients with IBD and acute diarrhoea (0-10%), IBS patients have a somewhat higher prevalence, while healthy individuals approach a prevalence of 30% (PCR-based data). So, the healthier a person is, the more likely is it that this person is a Blastocystis carrier! Also, if you have been diagnosed with D. fragilis - you are more likely also to have Blastocystis compared to people without D. fragilis.