Molecular characterization of Blastocystis species in Oregon identifies multiple subtypes

The association of Blastocystis species infections with gastrointestinal symptoms in humans is clouded by the variable presentation of disease and multiple lineages of the parasite that can infect humans and other animals. It has long been suspected that certain subtypes of Blastocystis may be more or less pathogenic, be restricted to certain hosts, or have limits to their geographic distribution. In the state of Oregon, USA, Blastocystis spp. are the most commonly encountered parasites in fecal specimens submitted for diagnostic evaluation, yet the diversity of subtypes is unknown. In this study, fecal samples were collected from individuals experiencing symptoms associated with blastocystosis and analyzed by polymerase chain reaction for presence of the parasite and DNA sequenced for subtyping. Five of 19 individuals tested positive for the parasite, all of which were also positive by previous ova and parasitology examination. DNA sequencing of the small subunit ribosomal DNA and elongation factor 1 alpha gene followed by phylogenetic subtyping identified five unique subtypes, representing Blastocystis subtypes 1, 2, 3, 4, and 8. No symptoms were consistently associated with presence or absence of infection, although abdominal pain and fatigue were reported by all infected individuals. Multiple subtypes are indicative of multiple sources of infection, suggesting more extensive surveys are required to understand the transmission of this parasite.