Genetic diversity and pathogenicity of Blastocystis.

<i>Blastocystis</i> is a unicellular, anaerobic protist which lives in the intestinal tract of diverse animals, including humans. It was found that the host specificity and the pathogenic potential of different isolates are correlated with sequence variations in the SSU-rRNA gene. Identification of the organism to the species level is still an unresolved challenge. Genetic diversity revisions have led to the identification of 17 subtypes (STs) within the <i>Blastocystis</i> genus, and 9 (ST1 to ST9) have been reported in humans with varying prevalence. Since the members of the genus revealed a large genetic diversity, several molecular modalities of subtyping methods have been developed. Numerous studies on conveying the pathogenic potential to the molecular subtypes are available, but they could not be compared or analysed with the different molecular techniques employed. The use of different approaches may give false positives during diagnosis and the possibility of missed infections. A review of recent scientific literature indicates that the development of PCR assays is needed for molecular epidemiology and for mixed infections in health and disease cohorts, and also to help identify sources of <i>Blastocystis</i> transmission to humans, as well as to identify potential animal and environmental reservoirs. This review summarizes some of the recent progress and improvements in <i>Blastocystis</i> research on genetic diversity, taxonomy, molecular epidemiology, pathogenicity and subtyping methods.