Showing posts with label metronidazole. Show all posts
Showing posts with label metronidazole. Show all posts

Wednesday, October 16, 2013

Dying to know about Dientamoeba?

It's difficult to say 'Blastocystis' without saying 'Dientamoeba fragilis'. Both parasites tend to be extremely common in countries where other intestinal parasites (e.g. Entamoeba, Giardia, Cryptosporidium) are of low endemic occurrence, and they are often seen together in patient samples. It is only due to the recent introduction of DNA-based diagnostic methods (PCR) that we now know that these parasites are much more common than previously anticipated.

So, while I'm trying to encourage guest bloggers, I thought I'd introduce a 'guest star' - Dientamoeba!

Dientamoeba fragilis trophozoites with the characteristic binucleated feature.
The parasite belongs to the trichomonads, which also comprise parasites such as Histomonas meleagridis (the cause of 'blackhead disease' in turkeys) and - more distantly - Trichomonas vaginalis.

At our Parasitology Lab at Statens Serum Institut in Copenhagen we have been using real-time PCR for specific detection of Dientamoeba fragilis in faecal samples from patients with gastrointestinal symptoms for quite a few years now. In the period of 2008-2011 we analysed 22,484 stool samples for D. fragilis. The overall prevalence of the parasite in these samples was 43% but depended mainly on age (Figure 1). D. fragilis prevalence appears to fluctuate dramatically depending on the age group. Highest prevalence was seen among 7-year-olds, and a second 'peak' is seen in the parental age suggesting that infected children pass on infections to their parents. 



Figure 1:  Prevalence of D. fragilis as a function of age. (For more information, see Röser et al., 2013b).

Intestinal protozoa are transmitted faecal-orally and most of them have a cyst stage. However, a few protozoa appear not to have a cyst stage, among them D. fragilis. There is a lot of evidence that Histomonas meleagridis is transmitted by eggs of Heterakis gallinae, a nematode of galliform birds. Conspicuously, we recently demonstrated the presence of D. fragilis DNA in surface-sterilised eggs of Enterobius vermicularis (pinworm). The implications of this finding are unclear but could suggest a similar vector-borne transmission of D. fragilis.

As in so many other situations it is not possible to dish out simple guidelines as to when to test for and treat D. fragilis. It is clear that many carriers experience few or no symptoms at all, but there are several case reports demonstrating symptom relief in patients eradicated of D. fragilis. We published one such case recently in 'Ugeskrift for Læger' - the journal of the Danish Medical Association. Basically, the report describes lasting symptom relief after documented eradication of D. fragilis using high dose metronidazole. However, the patient's symptoms returned after a year, and  real-time PCR revealed D. fragilis positive stools. Eradication was achieved using paromomycin (250 mg x 3 for nine days).

Contrary to Blastocystis, this parasite exhibits remarkably limited genetic diversity. We recently analysed three different genetic loci (18S, actin, elongation factor 1-alpha), and we confirmed that only 2 genotypes exist, one of which is very rare. Genetically, however, the two genotypes are quite different, and it will be interesting to compare the nuclear genomes of the two, once they have become available.

Dientamoeba has been speculated to be a neglected cause/differential diagnosis of irritable bowel syndrome (IBS). We once found a statistical significant association between IBS and Dientamoeba; however, other more recent and more targeted studies (one of which is ongoing) have not confirmed this association. However, multiple factors could interact and analysing only simple associations such as symptoms related to parasite presence/absence may be a limiting approach; for instance, infection load/intensity may play a role, and other factors such as host genetics/susceptibility and microbiota ecology may be significant factors influencing on clinical outcome as well. On that note, we have observed some very low Ct values in our real-time PCR results for some of our D. fragilis positive patients, suggesting massive infections. D. fragilis infections are probably often long lasting (months), and if symptoms appear in the initial phase of infection only, cross-sectional studies of prevalence and clinical presentation will be potentially misleading. Large longitudinal cohort studies of pre-school children with monitoring of incidence of pinworm and D. fragilis infections would be extremely informative.

Dr Dennis Röser here at the SSI is currently finishing a randomised controlled treatment trial of D. fragilis in children, testing the clinical efficacy of metronidazole treatment versus placebo. Results are expected next year, so watch out for a 'D. fragilis special' by Dr Röser in 2014! It appears a lot easier to eradicate D. fragilis than Blastocystis - at least on a short term basis with metronidazole having an efficacy of about 70% or so (unconfirmed).

A couple of reviews free for download are available; please see literature list below or go here and here.

Suggested literature

Engsbro AL, Stensvold CR, Nielsen HV, & Bytzer P (2012). Treatment of Dientamoeba fragilis in patients with irritable bowel syndrome. The American Journal of Tropical Medicine and Hygiene, 87 (6), 1046-52 PMID: 23091195   

Johnson EH, Windsor JJ, & Clark CG (2004). Emerging from obscurity: biological, clinical, and diagnostic aspects of Dientamoeba fragilis. Clinical Microbiology Reviews, 17 (3) PMID: 15258093

Ogren J, Dienus O, Löfgren S, Iveroth P, & Matussek A (2013). Dientamoeba fragilis DNA detection in Enterobius vermicularis eggs. Pathogens and Disease PMID: 23893951  

Röser D, Nejsum P, Carlsgart AJ, Nielsen HV, & Stensvold CR (2013a). DNA of Dientamoeba fragilis detected within surface-sterilized eggs of Enterobius vermicularis. Experimental Parasitology, 133 (1), 57-61 PMID: 23116599   

Röser D, Simonsen J, Nielsen HV, Stensvold CR, & Mølbak K (2013b). Dientamoeba fragilis in Denmark: epidemiological experience derived from four years of routine real-time PCR. European Journal of Clinical Microbiology & Infectious Diseases : official publication of the European Society of Clinical Microbiology, 32 (10), 1303-10 PMID: 23609513  

Stark DJ, Beebe N, Marriott D, Ellis JT, & Harkness J (2006). Dientamoebiasis: clinical importance and recent advances. Trends in Parasitology, 22 (2), 92-6 PMID: 16380293  

Stark D, Barratt J, Roberts T, Marriott D, Harkness J, & Ellis J (2010). A review of the clinical presentation of dientamoebiasis. The American Journal of Tropical Medicine and Hygiene, 82 (4), 614-9 PMID: 20348509

Stensvold CR, Clark CG, & Röser D (2013). Limited intra-genetic diversity in Dientamoeba fragilis housekeeping genes. Infection, Genetics and Evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases, 18, 284-6 PMID: 23681023

Stensvold CR, Lewis HC, Hammerum AM, Porsbo LJ, Nielsen SS, Olsen KE, Arendrup MC, Nielsen HV, & Mølbak K (2009). Blastocystis: unravelling potential risk factors and clinical significance of a common but neglected parasite. Epidemiology and infection, 137 (11), 1655-63 PMID: 19393117

Wednesday, July 10, 2013

This Month In Blastocystis Research (JUL 2013)

The open access journal 'Tropical Parasitology' (published by the Indian Academy of Tropical Parasitology) has included a symposium on Blastocystis in their January-June (Vol. 3) issue (available here). The symposium comprises three papers; one is on "taxonomy, biology and virulence", the next is on genetic diversity and molecular methods for diagnosis and epidemiology, and the last one is on treatment controversies. I believe that it may take quite a while before these papers will appear in PubMed.

The first paper written by Drs Parija and Jeremiah sums up a few of the aspects related to (especially historical) taxonomic issues and very little on the actual biology of Blastocystis. Meanwhile, there is quite a substantial section on Blastocystis morphology. Regarding virulence, the authors mention the possibility that differences in virulence may be due to differences in subtypes, but that subtyping alone does not predict pathogenicity which in part may be due to varying levels of intra-subtype genetic variation. The authors also briefly mention some of the morphological and phenotypical observations that have been associated with 'pathogenic Blastocystis', such as the amoeboid stage, large cells, rough surface, slow growth rate, and increased binding to lectins. It is always interesting to speculate on such associations, but it must be kept in mind that results from in-vitro experiments may not necessarily reflect in-vivo situations.

One topic that keeps popping up in the literature - and also in two of the papers here in this symposium - is the possibility of 'amoebic forms' of Blastocystis being associated with symptomatic infection. This hypothesis was introduced in 2006 by Tan and Suresh, I believe; Scanlan (2013) speculated that amoeboid forms might be the nutrient acquiring form potentially selecting for bacterial virulence or certain bacterial communities through grazing; please go here for more thoughts from a previous blog post.

My own experience on Blastocystis morphology mainly stems from looking at cultures, and since we practically only get isolates from patients with gastrointestinal disease, I don't know what Blastocystis cultures from asymptomatic individuals look like. A dear colleague of mine - Marianne Lebbad, a brilliant Swedish parasitologist with many years in business - sent me the picture below (light microscopy of a faecal concentrate) and speculates that Blastocystis might be able to form groups/clusters of cells, maybe even with the ability to form a mono-layer on the surface of the gut mucosa? I've never observed the cluster formation in cultures, but then again, we have no idea of whether the stages seen in in vitro cultures (microaerophilic environment) are identical to the in vivo stages (strictly anaerobic), and exactly how Blastocystis lives and multiplies in the colon... Anyway, the idea of biofilm comes into mind. It would be nice to learn more from colleagues with a similar experience.

Light microscopy of Blastocystis apparently forming a cluster of cells; we wonder whether the cells are in fact 'glued' together and if so, how? Courtesy of Dr Marianne Lebbad.

Moving on to the next paper, this one was written by me and deals mostly with issues and developments within the field of diagnostics, molecular characterisation, and molecular epidemiology. The target audience comprises clinical microbiologists and those involved in Blastocystis epidemiology and genetic diversity research. Included is a table, which is basically a reproduction of the one included in the recent paper by Alfellani et al. (2013) displaying the distribution of subtypes in humans across different geographical regions. I hope that the open access feature of this paper will prompt even more researcher into Blastocystis epidemiology! At least it is currently listed on the site as 'popular'!

The third paper in the string is written by Drs Sekar and Shanthi. These authors put emphasis on the conspicuous lack of data on the metabolic processes of Blastocystis, making it difficult to establish how to best approach antibiotic intervention; we must anticipate that with more genomic and transcriptomic data analyses arriving within a foreseeable future we will soon know much more about this. They also reiterate what has been put forth by many, namely that differences in eradication may boil down to differences in drug susceptibility, which again may be due to a variety of reasons, including genetic diversity, which is extreme in Blastocystis.

According to these authors, 'therapy should be limited to patients with persistent symptoms subsequent to a complete work up for alternative etiologies'; at the present stage this appears sensible, although clinicians would probably appreciate a clearer definition of 'symptoms'!

The review goes through some of the drugs most commonly used for treating Blastocystis, including metronidazole, paromomycin and co-trimoxazole, but also includes a few data on the use of the probiotic Saccharomyces boulardii in attempts to eradicate Blastocystis. There is not very much on the mechanisms of drug action, - it's more like a summary of data coming out from different studies, including the few placebo-controlled ones.
Regarding co-trimoxazole (which is also known as 'Bactrim' or 'Septra') this drug combo is often administered to HIV-patients prophylactically against Pneumocystis. In a study of parasites in Danish HIV patients, only 6/96 patients were given co-trimoxazole (unpublished data); two of these patients had Blastocystis. Hence, one 'alternative' way of finding out about the efficacy of co-trimoxazole on Blatocystis is to test the stools from patients undergoing long-term Pneumocystis prophylaxis comparing these patients to a cohort not receiving Pneumocystis prophylaxis but otherwise similar.

I find it a bit peculiar though to go through a review on treatment data that does not at one single point mention the need for sensitive diagnostics when evaluating courses of treatment and the identification of carriers and non-carriers. Also, there are some passages which are quite difficult for me to follow, for instance p. 36, second column, bottom section.

I hope that this symposium will inspire some of our colleagues and contribute to an increased understanding of Blastocystis.

References:

SYMPOSIUM

Parija SC & Jeremiah SS (2013). Blastocystis: Taxonomy, biology and virulence Tropical Parasitology DOI: 10.4103/2229-5070.113894
 
Stensvold CR (2013). Blastocystis: Genetic diversity and molecular methods for diagnosis and epidemiology Tropical Parasitology DOI: 10.4103/2229-5070.113896  

Sekar U & Shanthi M (2013). Blastocystis: Consensus of treatment and controversies Tropical Parasitology DOI: 10.4103/2229-5070.113901

OTHER:

Scanlan PD (2012). Blastocystis: past pitfalls and future perspectives. Trends in parasitology, 28 (8), 327-34 PMID: 22738855

Stensvold CR, Nielsen SD, Badsberg JH, Engberg J, Friis-Møller N, Nielsen SS, Nielsen HV, & Friis-Møller A (2011). The prevalence and clinical significance of intestinal parasites in HIV-infected patients in Denmark. Scandinavian Journal of Infectious Diseases, 43 (2), 129-35 PMID: 20936912  

Tan TC & Suresh KG (2006). Predominance of amoeboid forms of Blastocystis hominis in isolates from symptomatic patients. Parasitology Research, 98 (3), 189-93 PMID: 16323025

Saturday, June 15, 2013

Blastocystis - 'Monsters Inside Me'

I woke up this morning, grabbed my smartphone and went on to check my Blastocystis Google Alert. There was one entry, and this was the one:




Now, I could probably do a post with hundreds of examples showing how the internet abounds with material that may misguide/misinform people on Blastocystis pathogenicity. As such, this video is a nice example of how you can diligently manipulate people into thinking that severe, debilitating disease can be caused by Blastocystis.

Now, before I move on, I have to say that if this is a documentary, I'm very sorry for the couple in this video who have suffered the pain and consequences of sudden debilitating illness. Precautions have to be taken when you are exposed to sewage to avoid contracting infections.

The symptoms that are described in the video - including the weight loss - could be attributable to many different bacterial and viral pathogens, even parasites such as Cryptosporidium and maybe also Giardia; to this end, the video provides us with no information on other pathogens found in the patient's stool. Even in the event that Blastocystis was the only potential pathogen found, other pathogens may have been overlooked if sensitive diagnostics were not taken into use.

It is possible that Bill Wilson contracted Blastocystis only after signing on to his plumbing contract, but it is also possible that he had it a long time before. Many of us (up to 30% of the healthy Danish population) are colonised, and colonisation is often chronic.

We are informed that the patient receives a course of metronidazole, a drug that is often used to treat Blastocystis, but which in fact has a limited efficacy in vivo when used alone. Bill apparently clears his symptoms after metronidazole treatment, but we do not know whether in fact Bill also clears his Blastocystis infection, which could be determined by post-treatment stool tests. Metronidazole is capable of clearing a large number of anaerobic bacterial and protozoan species, and it is not unlikely that the drug has eradicated one or more pathogens that Bill could have contracted during his work (or elsewhere), and so symptom relief may be due to clearance of a non-Blastocystis pathogen instead.

Finally, it may be so that symptom disappearance coincides with spontaneous pathogen resolution. Cryptosporidiosis, for instance, can cause quite debilitating disease even in immunocompetent individuals, causing the infected individuals to lose a lot of water due to diarrhoea lasting for days or even weeks, but the disease is usually self-limiting.

So, this video tells a story that makes the audience automatically think that Bill Wilson's disease is due to Blastocystis. Apart from the statement 'Complications from a Blastocystis hominis infection can be fatal' and the explanation of how metronidazole works on Blastocystis, there is not really any statements or information in the video that do not make sense; the video is just put together in a way so that the viewer automatically deduces that Blastocystis is the culprit. A diligent act of manipulation!

Please note that this post is about how information on Blastocystis can be conveyed to an audience and not about the particular case as such.

Reference:

Stensvold CR, Smith HV, Nagel R, Olsen KE, & Traub RJ (2010). Eradication of Blastocystis carriage with antimicrobials: reality or delusion? Journal of clinical gastroenterology, 44 (2), 85-90 PMID: 19834337

Saturday, February 23, 2013

Blastocystis aux Enfers

We tremble at the thought of being devoured by a ferocious animal, - of ending our days in a narrow, suffocating slimy tube covered in acidic, nauseating glaze! Remarkably, for some eukaryotic beings, this is the only way forward if they want to carry on with their lives! Intestinal protists such as Blastocystis are in a state of hibernation when outside our bodies and the only thing that may rouse these Sleeping Beauties to action is the passage through low pH enzyme ponds. They thrive, grow and raise their progeny only in the swampy Tartarus of our large intestines; they bequeath to their offspring the affinity for this gloomy, filthy slew; this murky, densely populated, polluted channel, and when the pool of poo becomes all too arid, they know it’s time to buckle up, shut down, and prepare themselves for the great unknown which can potentially mean death to them if eventually they are not lucky enough to be gulped down by another suitable host.

Source
And yet, despite their remarkable modesty and humble requirements these little buggers are being bullied by their inhospitable human hosts; we’d throw anything at them to force them out, organic and inorganic compounds meant to arrest or even kill them. But the whelps of Blastocystis appear extremely resilient, which may hold the key to part of their success; they stay afloat on the Styx of our bowels. In order to eschew Flagyl, perhaps they bribed Phlegyas?

I think it's sometimes useful to put things into a completely different perspective. In any event, from an evolutionary biology standpoint it is highly interesting that a genus which is genetically related to water molds such as those causing potato blight and sudden oak death, has so successfully adapted to a parasitic, anaerobic life style, capable of protractedly colonising a plethora of very diverse host species including members of primates, other mammals, birds, reptiles, amphibians and arthropods and thereby evading innate and adaptive immune defenses from such a diverse range of hosts. One could be inclined to say: Well done! But which is it? Parasitism? Commensalism? Mutalism? Symbiosis? And what will happen to Blastocystis in the future? Will this successful crusader eventually succumb to our avid but maybe imprudent war strategies? And if so, what will happen to us after removing such a common player from our intestinal ecosystems?

Tuesday, December 18, 2012

Blastocystis Highlights 2012

2012 is coming to an end and it is also time for taking stock of the year Blastocystis-wise. We saw many significant scientific papers, among them a paper by Poirier and colleagues, predicting a potential role for Blastocystis in irritable bowel syndrome (IBS), based on analysis of their recent genome data.They propose that Blastocystis is genetically armed with the equipment necessary to cause intestinal dysbiosis, and potentially IBS, which may be a cause of dysbiosis. Indeed, members of this group found that the Blastocystis genome encodes various proteases and hydrolases that, if secreted, may be involved with perturbations of the gut flora; however, we need transcriptional profiling or similar studies to find out, whether these enzymes are actually expressed. Some species of Entamoeba are also in possession of multiple "virulence genes", but for some species they apparently remain un-expressed, and most Entamoeba species are still considered harmless.


Friday, October 26, 2012

The "Flagyl" Poll

For some reason the "Flagyl" poll in the right side bar of this blog was reset; the number of votes was approaching 100. The question was

"For those who have received metronidazole (Flagyl or Protostat) treatment for Blastocystis, please indicate whether you experienced no, transient or permanent improvement (or none of the above)"

The interesting thing is that there was a tie between "no improvement" and "transient improvement", and although this poll could have been heavily biased in numerous ways, it is still completely in line with our experience: Many patients report transient alleviation of symptoms, while others have no clinical benefit from Flagyl. Flagyl is an antibiotic targeting a wide range of bacteria and single-celled parasites. It is sometimes successful in terms of eradicating Dientamoeba fragilis, one of the most common parasites in the human intestine, and a parasite which may cause symptoms especially in children (we are currently conducting a randomised control clinical trial at Statens Serum Institut to explore clinical and microbiological effect of metronidazole treatment of children with D. fragilis).

Many people will get diagnosed with Blastocystis without knowing whether they might also be positive for D. fragilis (and vice versa). It is a complex situation, since both parasites are common, they are difficult to detect unless you use PCR or other specialised analyses, and in most labs they are not tested for on a routine basis. And if they happen to be part of the panel of organisms that is tested for, it may be so that insensitive methods are used for their detection, which means that only a fraction of the cases will be detected. So, this is a bit of a conundrum in itself!

So, it's not easy to know what causes the temporary alleviation in some patients. Is it due to parasite recrudescence? Is it due to parasite eradication with subsequent re-infection? And which parasite? Blastocystis? Dientamoeba? Any others? Or, is it due to perturbation of the intestinal flora in a "positive" direction, which is then gradually going back to normal? Placebo effect? There are possibly many more explanations...

However, deep sequencing of faecal samples pre- and post treatment of parasite-positive patients will probably answer many of our questions...

Literature:
Engsbro AL, Stensvold CR, Nielsen HV, & Bytzer P (2012). Treatment of Dientamoeba fragilis in Patients with Irritable Bowel Syndrome. The American journal of tropical medicine and hygiene PMID: 23091195

Engsbro AL, & Stensvold CR (2012). Blastocystis: to treat or not to treat ... But how? Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 55 (10), 1431-2 PMID: 22893582

Monday, October 8, 2012

Additional Comments on Blastocystis Treatment

I want to thank for the many emails I get! Unfortunately, I cannot respond to each one of them, in part due to time limits, in part since some of them are a bit off my topic or very difficult to answer. However, a few words on Blastocystis treatment (again!), which will hopefully satisfy some of the readers: 

Differences in the reported efficacy (microbiological and clinical cure) of certain drugs or drug combinations may be due to one or more of the following:

1) Actual differences in efficacy due to differences in pharmacokinetics, and -dynamics. Some drugs used for treatment of intestinal parasites are absorbed quickly from the intestine, while others are practically not absorbed at all (but stay in the intestinal lumen). For instance: Metronidazole is absorbed almost 100% in the proximal part of the intestine and may very well fail to reach Blastocystis, which resides is in the large intestine.

2) Different methods are used for evaluating treatment efficacy. If insensitive methods are used, the efficacy of any drug will be overestimated. Culture in combination with PCR is clearly advantageous in terms of evaluating microbiological efficacy since it will detect viable cells (see previous blog posts).

3) Drugs used in Blastocystis treatment may have broad spectrum antibiotic activity (e.g. metronidazole) and thus affect the surrounding microbiota, which again may influence the ability of Blastocystis to continue establishment. Hence indirect drug actions may play a role too. 

Could vegetables contribute to Blastocystis transmission?

4) Diet. What types of food do we eat? I notice that some people undergoing treatment for “blastocystosis” are cautious about eating carbs, for instance, and turn to vegetables only or at least non-carb diets, thinking that by cutting out carbs, they will cut off the "power supply" to Blastocystis. I’m not sure that this approach is very effective and it’s also important to acknowledge that the processing and metabolism of the foods that we ingest are complex. I hope to be able to do a blog post once on short-chain fatty acids, for instance. Again, changes in our diets may influence our bacterial flora which again may have an impact on Blastocystis. Importantly, we don’t know much about potential transmission of Blastocystis from raw vegetables and whether this could be a potential source infection (vegetables contaminated with Blastocystis).

5) Which leads to the next issue: The issue of re-infection. With so many people infected by Blastocystis (probably between 1-2 b people) it is likely that many of us are often exposed to the parasite. If we receive treatment but are not cut off from the source of infection, microbiological and clinical cure will be short-lived if at all possible.

6) Compliance - some drugs have serious adverse effects, and so, failure to reach microbiological cure may stem from failure to comply with drug prescriptions.

7) Differences in drug susceptibility. There is evidence from in vitro studies that Blastocystis subtypes exhibit differences in drug susceptibility.

In the absence of sound data that take all of the above factors into account, it is not possible for me (or anyone) to predict exactly which drug (combo) that will work and which will not. I think that it is important that GPs or specialists who take an interest in treating Blastocystis collaborate with diagnostic labs that are experts on Blastocystis diagnostics. If any drug or drug combo enabling microbiological cure can be identified, such pilot data can be used to design randomised controlled treatment studies that again will assist us in identifying whether Blastocystis eradication leads to clinical improvement.

I will try and provide some thougths on other future directions for Blastocystis research soon. Stay tuned!

Saturday, August 18, 2012

To Treat or Not To Treat... But How?

In the "To Treat or Not To Treat" series (please look up previous post here), we have come to the "...But How?" episode.

Blastocystis may be susceptible to a number of drugs - in vitro. In vitro is not the opposite of in vivo. In vitro just  means that the test has been done on an organism that has been isolated from its usual habitat and tested e.g. in a flask, test tube, etc. In the lab, strains can be challenged and manipulated in multiple ways, but there is no guarantee that the outcome of an in vitro susceptibility test is reproducible in vivo, i.e. when the organism is challenged in its natural habitat and under "natural" conditions. Hence, if you test Blastocystis against metronidazole or any other compound (such as iodine) in vitro, and you observe an effect, you cannot rely on being able to reproduce the effect in vivo. This is due to a variety of reasons including pharmaco-kinetics and pharmaco-dynamics, including the ability of the drug to reach the parasite in its ecological niche, impact of the drug on other micro-organisms, drug interactions, strain-dependent differences in susceptibility (including inherent or acquired resistance), etc.

We recently described a case in which a woman with irritable bowel syndrome (according to the Rome III criteria) had both Blastocystis subtype 9 (ST9) and Dientamoeba fragilis. In order to try and eradicate the parasites and to see whether any eradication would impact on her clinical situation, she received multiple courses of antibiotic treatment:

1. Metronidazole (750 mg x 3/d for 10 days)
2. Tetracycline (500 mg x 4/d for 10 days)
3. Trimethoprim + Sulfamethoxazole (TMP 800 mg + SXT 160 mg x 2/d for 7 days)
4. Mebendazole + Metronidazole (100 mg x 2 separated by 2 weeks; subsequently metronidazole as in 1.)
5. Paromomycin + Metronidazole (PM 500 mg + MZ 170 mg x 3/d for 10 days)

Mebendazole was given to the entire household due to suspicion of pinworm infection running in the family that could be a potential reservoir of D. fragilis (re-)infection.

No clinical alleviation was seen throughout this period.

PCR-based detection of Blastocystis and D. fragilis was used to evaluate  faecal samples 5-10 days post-treatment: Microbiological effect was seen only on D. fragilis which was cleared only after treatment with PM + MZ (5).

So, Blastocystis "survived" this series of antimicrobial treatment. In Denmark, no further relevant treatment options are available for general use (actually, even the use of Humatin (PM) needs a special license).

None of the patient's family members or pets were found to be colonised by the same strain, probably indicating that there was no "local" reservoir for ST9, and that the repeated finding of ST9 was not due to re-infection.

It may be so that Blastocystis requires a certain intestinal bacterial flora to establish. However, we expect that substantial perturbations in the intestinal flora must have taken place during the patient's various treatments, and therefore Blastocystis must be able to quickly overcome and adapt to such perturbations. It may add to the conundrum that in this case the woman harboured ST9, which is only very rarely seen in humans, and we might therefore deduce that its presence would be more volatile. No animal/environmental reservoir has yet been identified for ST9.

There is no doubt that microbiomic profiling of the intestinal flora would be of great benefit in a case like this. If data could be achieved on the impact of these drugs on the relative bacterial structure and function by metagenomic approaches, then this would allow us to explore the changes in the general flora that Blastocystis is capable of withstanding. Certainly, none of these drugs had a measurable in-vivo protistocidal effect on Blastocystis when administered as shown.

I re-emphasise that it is far from certain that Blastocystis is capable of inducing disease, directly or indirectly, and hence, we do not know if, and in which situations, we should aim at eradicating it. Suffice it to say, that in our hands and with the compounds that are available for general use in Denmark, it is apparently extremely challenging to eradicate Blastocystis, if at all possible.

Microbe Resilience (Source)

Further reading:

Coyle CM, Varughese J, Weiss LM, & Tanowitz HB (2012). Blastocystis: to treat or not to treat... Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 54 (1), 105-10 PMID: 22075794

Engsbro AL, & Stensvold CR (2012). Blastocystis: To Treat Or Not To Treat...But How? Clinical infectious diseases : an official publication of the Infectious Diseases Society of America PMID: 22893582

Stensvold CR, Smith HV, Nagel R, Olsen KE, & Traub RJ (2010). Eradication of Blastocystis carriage with antimicrobials: reality or delusion? Journal of clinical gastroenterology, 44 (2), 85-90 PMID: 19834337

Friday, May 18, 2012

Blastocystis network on Facebook

This blog includes everything from updates on Blastocystis research, paper evaluations, polls, links, lab SOPs, to network opportunities and social interaction suggestions for all of us interested in Blastocystis. This time I want to guide your attention towards the Blastocystis network on Facebook. This is a good place to discuss personal experience with e.g. Blastocystis diagnosis and treatment and symptoms. The group is called "Blastocystis sp. (Blastocystis hominis and sp.)". If you have any experience and comments on Flagyl/Protostat (metronidazole), CDD regimens, including Secnidazole, Nitazoxanide, Furazolidone, Septrim (or Bactrim), Diloxanide Furoate, or other agents, please look up the group and share... We need your experience and views.

Monday, May 7, 2012

Blastocystis: To Treat or Not to Treat...

This year, Coyle et al. published a Clinical Practice paper in Clinical Infectious Diseases, a journal with a 5-year impact factor of almost 8. It is still difficult to get papers on Blastocystis published in clinical, peer-reviewed journals of major impact, probably due to the fact that evidence of Blastocystis' pathogenicity is so far only indicative, so it is great to see that the authors have managed to get their manuscript past those iron doors!

A few issues have come to my attention. When reading the abstract the reader will get the impression that subtypes are synonymous with genotypes, which is not the case. In the case of Blastocystis, a subtype is equivalent to a species; one of the reasons why we haven't allocated species names to Blastocystis from humans, other mammals and birds yet, is that we do not have sufficient data on genetic diversity and host specificity to come up with relevant names.

It says in the first page (pdf) that Blastocystis subtype (ST) 3 is found only in humans, which is not true. This subtype is common in non-human primates and can be seen in other, larger animals, including dogs, and also birds, if I remember correctly. However, so far, we only have multilocus sequence typing data from human and non-human primates, and these data indicate that ST3 found in non-human primates is often different from ST3 found in humans.

The authors recommend that asymptomatic individuals with few cysts should not be treated. Then what about asymptomatic individuals with many cysts? Also, with the diagnostic short-comings of microscopy of faecal concentrates, the suggested cut-off at 5 organisms per visual field appears arbitrary and, in best case, fortuitous.

In the abstract, the authors state that metronidazole is the drug of choice, although they appear to be quite aware that this drug has limited effect in terms of eradicating Blastocystis. So, why is metronidazole the drug of choice? Blastocystis is a parasite lodged primarily in the large intestine, and therefore we must anticipate that metronidazole often fails to reach the the parasite in sufficient concentrations due to absorption proximally in the gut. Luminal agents, such as paromomycin, are probably more likely to work, maybe in combination with metronidazole, although we have had a case, where even this combination was not effective.


When reviewing studies of treatment, it is important to acknowledge that insensitive methods have been used to evaluate drug efficacy. Culture combined with PCR is in my opinion the best method available in this respect. I prefer adding culture to the test, since culture detects viable Blastocystis (as opposed to PCR which will detect both viable and non-viable cells). Future randomised controlled treatment studies should therefore use culture and PCR to identify carriers both pre- and post-treatment. Whether Blastocystis-positive stool post-treatment is due to recrudescence, resistance or reinfection is not easily evaluated, but some useful information can be achieved by multi-locus sequence typing of isolates pre- and post-treatment.

Literature cited:

Coyle CM, Varughese J, Weiss LM, & Tanowitz HB (2012). Blastocystis: to treat or not to treat... Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 54 (1), 105-10 PMID: 22075794  

Stensvold CR, Alfellani M, & Clark CG (2012). Levels of genetic diversity vary dramatically between Blastocystis subtypes. Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases, 12 (2), 263-73 PMID: 22116021  

Stensvold CR, Smith HV, Nagel R, Olsen KE, & Traub RJ (2010). Eradication of Blastocystis carriage with antimicrobials: reality or delusion? Journal of clinical gastroenterology, 44 (2), 85-90 PMID: 19834337

Saturday, March 31, 2012

Blastocystis Treatment

In my opinion, in many cases we should "leave Blastocystis alone". In some cases, however, treatment may be warranted. However, currently there are no convincing drug regimens. RCTs needed.
For more information, please consult this review.