Blastocystis in the human gastrointestinal tract - commensal or "silent" pathogen?

Blastocystis is a unicellular anaerobic microorganism inhabiting the human and animal gastrointestinal tract (GIT). It is the most abundant representative of eukaryotes reported in human feces and found in approx. a billion people worldwide. Despite the common occurrence, its direct pathogenicity and status among other, more significant, GIT parasites remain unclear. Blastocystis colonization is associated with various non-specific clusters of symptoms, such as diarrhea, abdominal pain, flatulence, or nausea and is often diagnosed in patients with irritable bowel syndrome, ulcerative colitis, or urticaria. Controversy persists mainly because of the detection of Blastocystis even in asymptomatic patients and the unclear mechanism of its potential pathogenicity. Also, for the reasons mentioned above, no treatment guidelines are available.