Blastocystis is a single-celled, algae-like intestinal parasite. Aside from yeasts, Blastocystis is the most common eukaryotic (ie non-bacterial) organism found in our gut, and over a billion people may be colonized.
However, the public health significance of Blastocystis colonization is not fully understood. Irritable bowel syndrome (IBS) has been linked to colonization by Blastocystis. This may be due to the fact that the symptoms that can arise during colonization are quite reminiscent of IBS symptoms and both conditions are common. While some studies have found an association between Blastocystis and IBS, many have not.
Once established, this parasite can reside in the intestine for months or years. Although metronidazole is often prescribed for symptomatic infection (and when other causes of symptoms have been ruled out), the use of sensitive diagnostic methods such as PCR has shown us that, in most cases, this drug does not eradicate Blastocystis, even after 10 days of max. dosing, and currently, there is no convincing drug regimen.
Blastocystis comprises many different species (subtypes (ST)), some of which are common in humans. While subtypes 1, 2, and 3 are common in all parts of the world and appear to be equally prevalent in patients with diarrhea and in the general population (ie, people without intestinal complaints), ST4 appears to occur primarily in patients with diarrhea and /o IBS and ST4 is therefore a subtype currently under intense scrutiny. In the meantime, I think most ST3 infestations are harmless. This is supported by some of our recent data showing that ST3 genetic diversity is extensive, suggesting coevolution with humans over a long period. Contrary to this is ST4, which has a nearly clonal population structure, suggesting a recent entry into the human population. Furthermore, ST4 appears to have a restricted geographic distribution, being relatively rare outside of Europe. However, we are still lacking in data, and strict inferences about ST distribution and role in disease are still premature.
If ST4 is pathogenic while other common subtypes are harmless commensals, this is not the first time that parasites that cannot be distinguished by morphology differ in terms of the ability to cause disease. A similar situation is observed in those species of amoebas called Entamoeba histolytica and Entamoeba dispar. While E. dispar is considered by most experts to be a commensal primarily indicating relatively recent exposure to fecal-oral contamination, E. histolytica can cause life-threatening invasive disease, including abscess formation primarily in the liver.
Many of us harbor Blastocystis, and most of us don’t know it. One of the interesting things about Blastocystis is why so many people harbor the parasite, while others don’t. Very little is known about Blastocystis in the environment and whether we are exposed to Blastocystis in food, such as vegetables or drinking water. The prevalence of Blastocystis appears to be higher among adults and the elderly.
Until recently, Blastocystis was quite difficult to detect. Even today, inappropriate methods are used for detection, while sensitive tools such as culture and PCR are increasingly used in modern clinical microbiology laboratories to distinguish between carriers and non-carriers and to assess patients after treatment. . There is no doubt that diagnostic challenges and lack of recognition blastocystis‘The wide genetic diversity has hampered attempts to understand the clinical significance of Blastocystis.
Unbiased information on Blastocystis for the lay person is quite hard to come by and there are many sites on the internet trying to make Blastocystis a commercial success by perpetuating anecdotal data and information on the parasite for which there is currently no epidemiological, genetic or biochemical support.
For more information and updates on Blastocystis, please visit http://www.blastocystisblog.blogspot.com