Monday, January 14, 2013

A Penny For Your Thoughts

So, what should we do about Blastocystis? What do we want to know?

I believe the imminent answer to the latter question is easy: We want to know whether it’s pathogenic, whether we should treat it and how. But I also think that there are many other interesting aspects of Blastocystis which are also of broad interest to the general public, namely: How about the many cases of asymptomatic Blastocystis carriage? What does Blastocystis do in our guts? Could it have any potentially beneficial impact on our health?

Given the fact that Blastocystis has not been implicated in any outbreaks (admittedly: I guess that no one actually ever looked for Blastocystis in outbreak investigations... except for me!), I reckon that the chance of it being involved in acute diarrhoea is small. So, in that respect it's very different from the other intestinal protists such as Giardia, Cryptosporidium, Cyclospora, microsporidia, even Entamoeba histolytica. It's actually more reminiscent of helminth infections, which are are often chronic, and when light hardly give rise to symptoms (depending on species that is!).So I'm more thinking along the lines of co-evolution, adaptation, etc.

Maybe future research will call for a shift in paradigm, but until then I think that we should do what we already can, just at a larger scale and see where it takes us, namely:

1) Epidemiological associations: Investigation of subtype epidemiology in different human cohorts (IBS, IBD, healthy individuals (background populations), infectious diarrhoea, chronic diarrhoea) etc.  Barcoding is the state-of-the-art here, - easy, inexpensive, quick, and precise. Include studies of animals for knowledge on transmission dynamics. It’s important to display subtype distributions in many countries, since we have strong evidence that the distribution of subtypes may be very different among regions. MLST analysis is important for resolving zoonotic transmission issues.

2) Longitudinal studies of large cohorts of Blastocystis-naïve patients. Given the prevalence of Blastocystis, most of us are probably exposed and susceptible. Identify 500 negative individuals and follow them over 2-3 y and have them submit a stool sample every month + diary/questionnaire. Importantly: Use PCR for detection.Very costly though, but can be combined with analysis of other parasites and bacteria as a joint proposal.

3) Genome analysis: Denoeud and colleagues sequenced the entire genome of ST7, but we need the genomes of the common subtypes as well. ATCC strains are available in the event that axenic cultures cannot be obtained. And yes, we should definitely pursue the development of easily applicable axenisation protocols. Those people I know well and who tried to grow Blastocystis in the absence of bacteria failed to do so.

4) Transcriptome analysis: Analysis of gene expression. Requires genome data. Investigation into whether the virulence genes present in ST7 (and which may also be present in other subtypes) are actually expressed.

5) In-vitro systems. Enterocyte models with “live flora” including Blastocystis. Longitudinal studies. Monitoring of the structure and function of the flora and metabolites and enzymes excreted by Blastocystis.

6) Randomised controlled treatment studies with volunteers. If the CDD treatment (secnidazole, diloxanide furoate and co-trimoxazole) is as good as it promises, why not choose this combo for starters? Not sure about the adverse effect here, though, - they might be quite heavy, and some people are allergic to co-trimoxazole.

7) Real-time PCR screening for carriers. A few real-time PCRs have been published already, including the one we use in our lab (look up ref below). These assays enable quantification based on Ct-values and will therefore reveal potential associations between infection intensity and symptoms.

8) Blastocystis and the bacterial flora: Metagenomic studies + 16S/18S profiling.
These are just keywords / headlines, some of which I've already been mentioning. Some of these thing are difficult if at all feasible and there are many more things that can be done, especially in terms of in-vitro models, - but these may be quite expensive. Good thing is that NGS methods are now becoming less pricy. 

One thing is clear: we need multidisciplinary studies to obtain enough information for us to answer the first question in this post. 

(Wait, - is this post actually a re-description of Koch's Postulates for Blastocystis?? It would certainly be appropriate!).

Further reading:

Denoeud, F., Roussel, M., Noel, B., Wawrzyniak, I., Da Silva, C., Diogon, M., Viscogliosi, E., Brochier-Armanet, C., Couloux, A., Poulain, J., Segurens, B., Anthouard, V., Texier, C., Blot, N., Poirier, P., Ng, G., Tan, K., Artiguenave, F., Jaillon, O., Aury, J., Delbac, F., Wincker, P., Vivarès, C., & El Alaoui, H. (2011). Genome sequence of the stramenopile Blastocystis, a human anaerobic parasite Genome Biology, 12 (3) DOI: 10.1186/gb-2011-12-3-r29

Stensvold, C., Ahmed, U., Andersen, L., & Nielsen, H. (2012). Development and Evaluation of a Genus-Specific, Probe-Based, Internal-Process-Controlled Real-Time PCR Assay for Sensitive and Specific Detection of Blastocystis spp. Journal of Clinical Microbiology, 50 (6), 1847-1851 DOI: 10.1128/JCM.00007-12

Alfellani, M., Stensvold, C., Vidal-Lapiedra, A., Onuoha, E., Fagbenro-Beyioku, A., & Clark, C. (2013). Variable geographic distribution of Blastocystis subtypes and its potential implications Acta Tropica DOI: 10.1016/j.actatropica.2012.12.011

Stensvold, C., Alfellani, M., & Clark, C. (2012). Levels of genetic diversity vary dramatically between Blastocystis subtypes Infection, Genetics and Evolution, 12 (2), 263-273 DOI: 10.1016/j.meegid.2011.11.002

Wawrzyniak, I., Texier, C., Poirier, P., Viscogliosi, E., Tan, K., Delbac, F., & El Alaoui, H. (2012). Characterization of two cysteine proteases secreted by Blastocystis ST7, a human intestinal parasite Parasitology International, 61 (3), 437-442 DOI: 10.1016/j.parint.2012.02.007


  1. Thanks for your thoughts. After reading your blog, first thing that comes to my mind is that research on Blastocystis and Dientamoeba fragilis is focused on proofing that the bug is pathogenic. Whereas I'm thinking of the Hygiene hypothesis... Did anyone ever tried to proof the opposite? Not that the two parasite species are part of a healthy intestinal environment, but like helminths, they may have an positive effect on the human immune system?

  2. You're comment is extremely relevant in my opinion, and if you enter "hygiene hypothesis" in the search box on this blog, you will see that I've been thinking along the same lines...

  3. As someone who has blastocystis, and is symptomatic, I just want to know how to eradicate it. Everything else is just icing on the cake.