For over a century, the clinical significance of Blastocystis has puzzled medical doctors scientists. After realising the extensive genetic diversity in Blastocystis, one of the current main hypotheses is that Blastocystis subtypes differ in terms of clinical significance. In other words: Symptoms, such as diarrhoea or other intestinal upset, may be associated only with one or more subtypes, while other subtypes are strict commensals.
Blastocystis is very difficult to eradicate and colonisation is chronic. Do symptoms caused by potentially pathogenic subtypes persist or do they develop initially only to diminish after host immunological adaptation? Do fluctuations in symptoms reflect fluctuations in parasite load? Such issues ire important when interpreting results generated from cross-sectional surveys of subtypes in various cohorts.
Moreover, intestinal symptoms are difficult to define. Diarrhoea may be defined by 3 stool passages per day or more, while many other symptoms can be very difficult to define, if at all possible. Irritable bowel syndrome (IBS) and - to some extent - food allergy may both be considered differential diagnoses of symptomatic Blastocystis infections.
IBS diagnosis is currently defined by the Rome III criteria, and there are at least three types of IBS, namely IBS with diarrhoea, IBS with constipation and IBS with a mixture of diarrhoea and constipation.
Symptoms may be experienced differently from person to person. While abdominal cramping is perceived mostly as a symptom and something unpleasant, flatulence may by many be seen as a sign of a "healthy tummy" (e.g. due to consumption of a high fibre diet), although "inconvenient". Some individuals may very well tolerate intermittent intestinal symptoms and do not consult their GPs or other health care professionals, while others may be much more sensitive to any changes in for instance stool patterns.
What some people do not realise is that many methods fail to detect Blastocystis. PCR and culture are the most sensitive methods, but are still only rarely used. Moreover, PCR is also suitable for the detection of Dientamoeba fragilis, which is a parasite often seen in co-infection with Blastocystis. These two parasites are probably the most common single-celled eukaryotes in the human intestine.
This means that complete and accurate microbiological make-ups are far from always performed. And so, incomplete microbiological examination coupled with differential diagnostic challenges, potential immunological adaptation and the very subjective components of symptom presentation renders our quest for clear-cut associations extremely challenging. Blastocystis will often be seen as the culprit of symptoms, possibly simply to the reason that it is the only potential microbial pathogen that has been demonstrated in a stool sample. Cohort studies using sensitive diagnostic methods for pathogen surveillance are expensive, but may be one of the few only ways forward with regard to epidemiological studies that can assist us in resolving the clinical significance of Blastocystis.
Blastocystis is very difficult to eradicate and colonisation is chronic. Do symptoms caused by potentially pathogenic subtypes persist or do they develop initially only to diminish after host immunological adaptation? Do fluctuations in symptoms reflect fluctuations in parasite load? Such issues ire important when interpreting results generated from cross-sectional surveys of subtypes in various cohorts.
Moreover, intestinal symptoms are difficult to define. Diarrhoea may be defined by 3 stool passages per day or more, while many other symptoms can be very difficult to define, if at all possible. Irritable bowel syndrome (IBS) and - to some extent - food allergy may both be considered differential diagnoses of symptomatic Blastocystis infections.
Symptoms may be experienced differently from person to person. While abdominal cramping is perceived mostly as a symptom and something unpleasant, flatulence may by many be seen as a sign of a "healthy tummy" (e.g. due to consumption of a high fibre diet), although "inconvenient". Some individuals may very well tolerate intermittent intestinal symptoms and do not consult their GPs or other health care professionals, while others may be much more sensitive to any changes in for instance stool patterns.
What some people do not realise is that many methods fail to detect Blastocystis. PCR and culture are the most sensitive methods, but are still only rarely used. Moreover, PCR is also suitable for the detection of Dientamoeba fragilis, which is a parasite often seen in co-infection with Blastocystis. These two parasites are probably the most common single-celled eukaryotes in the human intestine.
This means that complete and accurate microbiological make-ups are far from always performed. And so, incomplete microbiological examination coupled with differential diagnostic challenges, potential immunological adaptation and the very subjective components of symptom presentation renders our quest for clear-cut associations extremely challenging. Blastocystis will often be seen as the culprit of symptoms, possibly simply to the reason that it is the only potential microbial pathogen that has been demonstrated in a stool sample. Cohort studies using sensitive diagnostic methods for pathogen surveillance are expensive, but may be one of the few only ways forward with regard to epidemiological studies that can assist us in resolving the clinical significance of Blastocystis.
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