Blastocystis

Blastocystis is an anaerobic, unicellular protist with a worldwide distribution. In mammalian and avian hosts, molecular studies have allowed the identification of at least 22 distinct ribosomal lineages, termed subtypes (STs), which could be considered separate species. At least 10 of these, ST1–9 and ST12, have been identified in humans, and all, except for ST9, have also been reported in non-human hosts, suggesting a potential for zoonotic transmission of the parasite. Despite being one of the most prevalent intestinal parasitic micro-eukaryotes, its role in health and disease remains controversial. Indeed, carriers are often asymptomatic but may also have acute and chronic disorders, including urticaria. However, in vitro studies allowed the identification of potential pathogenic mechanisms. Conversely, recent investigations have focused on associations between Blastocystis and gut microbiota characteristics, with multiple independent datasets suggesting that the protist is linked with a healthy gut microbiota, characterized by high bacterial species diversity, mainly potentially beneficial ones. Here we summarize some of the recent developments and advances in Blastocystis research, including updates on the taxonomy, molecular epidemiology, diagnostic methods, clinical significance, and genomics of this challenging microorganism.