Differences in clinical significance and morphologic features of Blastocystis sp subtype 3.

Blastocystis is a polymorphic intestinal parasite that is common in humans. A total of 51 asymptomatic and symptomatic patients positive for Blastocystis only were included in the study. Symptoms were mainly nonspecific gastrointestinal symptoms. Blastocystis isolates were xenically cultured and subtyped. Blastocystis species subtype 3 was the predominant subtype. Intrasubtype differences (vacuolar/amoeboid presence) in subtype 3 morphotypes were observed in 32 asymptomatic and symptomatic subtype 3 cases and could possibly be related to Blastocystis pathogenic potential. Diverse morphologic features (vacuolar transiting to amoeboid), probably reflecting the progression from an asymptomatic to a symptomatic state, were observed in an asymptomatic subtype 3 carrier who later had symptoms. Searching for amoeboid forms might be helpful to presumptively screen symptomatic patients with subtype 3 or to follow up an asymptomatic subtype 3 carrier in case symptoms become evident before antiprotozoal treatment was attempted. Further studies on the roles of morphologic features and variation within Blastocystis species subtypes as predictors of symptoms are encouraged.

Blastocystosis: an emerging or re-emerging potential zoonosis?

Blastocystis sp. is an intestinal protozoa that was formerly recognised as a yeast. However, it has since been classified in the Stramenopile Kingdom. In addition to being observed in humans, the disease has been diagnosed in a wide range of animals (mammals, amphibians, birds, reptiles and arthropods). Extensive genetic heterogeneity has been demonstrated. Blastocystis sp. subtypes 1 to 9 were recently considered to be of zoonotic origin. While some suggested that Blastocystis might play a pathogenic role in intestinal disorders in humans, others reported that there was no correlation. Furthermore, amoeboid forms of Blastocystis might be implicated in pathogenesis. In spite of recent reports, earlier data on the prevalence of the parasite suggest that blastocystosis could have occurred sporadically or continuously in the past. It might be speculated that in cases of zoonotic genotypes producing amoeboid forms, Blastocystis sp. infection might rather be considered a potential re-emerging zoonosis.