What is Dientamoeba fragilis?

Dientamoeba fragilis is a parasite belonging to the protozoan group. Protozoan parasites are very small single-celled parasites not visible with the naked eye. Among this larger group, Dientamoeba fragilis is classified with the trichomonads, which usually include parasites that are able to move around using typically four to six flagella. Interestingly, Dientamoeba fragilis does not possess any flagellum at all. Consequently, it was previously thought to be a member of the amoeba’s group, explaining its name. However, more studies about its genetic characteristics have allowed putting it in the flagellated group of trichomonads instead. It has then been hypotheses that Dientamoeba fragilis had previously had one or more flagella, but that it had lost them over the course of the evolution. As such, this parasite can now be considered as a kind of estranged amoeba coming from a flagellated ancestor. One interesting fact about it is that Dientamoeba fragilis is one of the smallest parasites residing in the human intestine, but it is susceptible to cause no symptom at all, as it has been detected in the faeces of many healthy people.

Notably, the protozoan parasite Dientamoeba fragilis was identified in 1918, almost a hundred years ago, and it was thought back then that it was harmless for humans. It remains considered as non-pathogenic for humans for a long time leading to a massive lack of scientific studies about it. Nowadays, despite increasing evidences to the contrary, the pathogenicity of this parasite remains controversial, as many old school physicians still have doubts about its potential to cause an actual disease, mainly because of the great number of asymptomatic cases, as well as its high occurrence with other parasites. It is indeed very common to find it concomitantly with other intestinal parasites, like pinworms (Enterobius vermicularis), which is a nematode from the parasitic group of helminths (worm), when testing somebody presenting gastrointestinal symptoms. Furthermore, many other intestinal protozoan parasites have also been reported concomitantly with Dientamoeba fragilis. As this parasite is very hard to diagnose, it also remains highly under-diagnosed using many standard diagnostic techniques, adding to the controversy about its pathogenicity. However, more and more physicians are now thinking that this parasite is able to cause a real gastrointestinal disease that they have called dientamoebiasis.

This specific parasite is present everywhere in the world. In fact, it has been detected in every inhabited territory on the planet. It has also been suggested that this parasite could be even more present in developed countries than in developing countries, which is quite rare for parasitic diseases. However, it is very difficult to assess the real number of infected people worldwide as it remains largely under-diagnosed, but some studies has suggested that Dientamoeba fragilis is potentially one of the most common gastrointestinal infectious diseases found in developed countries, especially in young adult and children. Furthermore, assessing accurately the actual prevalence of this parasite is complicated as most laboratories do not use the right techniques allowing the specific detection of this parasite and many actual infections with Dientamoeba fragilis remain unknown or attributed to other pathogens. However, some studies performed on healthy subjects have also suggested that almost everybody has specific antibodies against Dientamoeba fragilis within their body, meaning that almost everybody has, at least once in its life, encounters and fights against this parasite.

The controversy surrounding the real pathogenic potential of Dientamoeba fragilis has lasted for almost a century now. As this parasite was not considered as problematic for the human health, there is a great lack of scientific studies involving it. As such, very few things are known about its life cycle, its causes, its specific effective treatments and its behaviour once inside the human body. Many features attributed to this parasite are still unverified hypotheses and a lot of scientific studies are needed to really understand it. However, recent studies have suggested that some people supposedly suffering from the irritable bowel syndrome were actually infected with Dientamoeba fragilis. Some of them were even cured after following a specific treatment against this parasite. This kind of findings could potentially push the research world forwards. It could then not be surprising to see a lot more studies of this parasite in the future. Those would be very important in order to understand properly this underestimated pathogen.