Abstract
Blastocystis is a prevalent enteric protozoan that infects a variety of vertebrates. Infection with Blastocystis in humans has been associated with abdominal pain, diarrhea, constipation, fatigue, skin rash, and other symptoms. Researchers using different methods and examining different patient groups have reported asymptomatic infection, acute symptomatic infection, and chronic symptomatic infection. The variation in accounts has lead to disagreements concerning the role of Blastocystis in human disease, and the importance of treating it. A better understanding of the number of species of Blastocystis that can infect humans, along with realization of the limitations of the existing clinical laboratory diagnostic techniques may account for much of the disagreement. The possibility that disagreement was caused by the emergence of particular pathogenic variants of Blastocystis is discussed, along with the potential role of Blastocystis infection in irritable bowel syndrome (IBS). Findings are discussed concerning the role of protease-activated receptor-2 in enteric disease which may account for the presence of abdominal pain and diffuse symptoms in Blastocystis infection, even in the absence of fever and endoscopic findings. The availability of better diagnostic techniques and treatments for Blastocystis infection may be of value in understanding chronic gastrointestinal illness of unknown etiology.
Highlights
Blastocystis is a prevalent enteric protist that infects a variety of vertebrates
A study published by two physicians in California in 1988 reported symptoms of blastocystosis could usually be attributed to another cause and suggested that Blastocystis was non-pathogenic [5]
This study found that patients with irritable bowel syndrome (IBS)-d exhibited significantly higher protease levels in stool specimens, which were not found in patients diagnosed with diarrhea from acute infectious causes
Summary
Blastocystis is a prevalent enteric protist that infects a variety of vertebrates. Researchers have described asymptomatic and symptomatic infection in humans. Isolates that have been associated with symptomatic infection in humans have been found in asymptomatic carriers, so subtyping can not establish Blastocystis as a cause of illness in a particular patient. Many researchers identified a specific finding which they felt would be inconsistent with the behavior of a pathogen, such as a lack of correlation between the quantity of Blastocystis in stool samples and the patient's symptoms [133] or the absence of endoscopic findings in symptomatic infection [129]. Following an increase in detection rates of Blastocystis in the 1990's (see Appendix A in additional file 1), US studies show Blastocystis appearing frequently as a symptomatic mono-infection [14] with characteristics similar to Cryptosporidium parvum and Entamoeba histolytica. Studies may have fulfilled many criteria listed in a 1990 communication as necessary to establish the pathogenicity of Blastocystis [110]: fulfillment of Koch's postulates [48,104,141]; identification of an immune response [82,85,86]; definition of the pathogenesis [83,127,128,142]; identification of treatments [94,143,144]; and description of point source outbreak of diarrhea where Blastocystis was the cause [57,131,145]
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