Blastocystosis refers to a medical condition caused by infection with Blastocystis. Blastocystis is a protozoal, single-celled parasite that inhabits the gastrointestinal tracts of humans and other animals. Many different types of Blastocystis exist, and they can infect humans, farm animals, birds, rodents, amphibians, reptiles, fish, and even cockroaches.
The common protozoan parasite Blastocystis hominis that lives in the gut has been associated with irritable bowel syndrome, and it may be that Blastocystis hominis will turn out to be the cause of IBS in many patients. Better understanding of the biology and pathogenicity of Blastocystis hominis has only emerged quite recently.