ABSTRACT

Blastocystis is a nonmotile, extracellular, anaerobic stramenopile that inhabits the gastrointestinal tract of humans and animals. With a worldwide distribution, it is probably the most common eukaryotic microorganism in human gut. Contradictory findings about Blastocystis pathogenicity have emerged since its discovery in the beginning of the twentieth century, but it is obvious that most individuals infected with Blastocystis do not present any symptoms and indeed the organism may be an indicator of a healthy gut microbiota. However, a variety of nonspecific gastrointestinal complaints and some cutaneous lesions may be observed in symptomatic cases. In addition, Blastocystis has been linked to several chronic gastrointestinal disorders, such as irritable bowel syndrome (IBS) in certain population groups. Recent studies have indicated that Blastocystis pathogenicity is a complex phenomenon involving multiple factors. In the treatment of symptomatic cases, an efficient eradication strategy is not still described. Significant improvements have been achieved within the last decade in understanding the key concepts of the organism thanks to the increasing use of molecular methods and publication of two genome sequences. Many subtypes (arguable species) of Blastocystis and subtype-dependent host specificity of Blastocystis have been identified through phylogenetic analyses. Also investigations of zoonotic and waterborne transmission potentials of Blastocystis have yielded conclusive results. This chapter gives an overview of recent history and latest development relating Blastocystis.