Blastocystis is a common inhabitant of the human gut, colonizing at least one billion people at a prevalence ranging from <10% to 100% in healthy human populations globally. The majority of carriers remain asymptomatic, suggesting that Blastocystis is largely a commensal, though Blastocystis has also been implicated in disease in some people. However, there are no in vivo model systems in which to experimentally test the impact of Blastocystis on mammalian hosts and the gut ecosystem and determine which factors underlie these variable clinical outcomes. We evaluated a rat model for sustaining of a human-derived Blastocystis ST1 and assess colonization success and longevity. Because of the broad host range of Blastocystis, we compared the rat with three other rodent species to establish the reproducibility of our method. Blastocystis was introduced by esophageal gavage and colonization success evaluated by Blastocystis culture. Culture was also used to determine that all animals were negative prior to colonization and negative controls remain Blastocystis-free. In this study, Blastocystis ST1 established in 100% of the outbred rats (Rattus norvegicus) and gerbils (Meriones unguiculatus) challenged. Rats were colonized asymptomatically for more than one year, but Blastocystis ST1 was not transmitted between rats. Mus musculus strain CD1 and Mastomys coucha were not susceptible to Blastocystis ST1. Thus, rats appear to be a suitable in vivo model for studies of Blastocystis ST1, as do gerbils though testing was less extensive. This work lays the foundation for experimental work on the role of Blastocystis in health and disease.

Biology Centre Czech Academy of Sciences Institute of Parasitology České Budějovice Branišovská 31 370 05 Czech Republic

Biology Centre Czech Academy of Sciences Institute of Parasitology České Budějovice Branišovská 31 370 05 Czech Republic; Department of Medical Biology Faculty of Science University of South Bohemia Branišovská 31 370 05 České Budějovice Czech Republic

Department of Botany and Biodiversity Research Centre University of British Columbia Vancouver British Columbia V6T 1Z4 Canada; Department of Zoology University of British Columbia Vancouver British Columbia V6T 1Z4 Canada

Statens Serum Institut Artillerivej 5 DK 2300 Copenhagen S Denmark

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