Blastocystis hominis is a protozoan found in several forms (amoeboid, granular, vacuolar, cyst). It is one of the most frequently occurring human parasites. The invasive form are cysts. Infection occurs via the faecal-oral route through the consumption of contaminated water or food. Currently, it is believed that there are non-pathogenic and pathogenic strains of Blastocystis hominis. The latter are responsible for symptomatic blastocystosis.

Most blastocystis infections are asymptomatic. In clinical cases, the invasion of Blastocystis hominis is characterized by chronic, less frequently, acute diarrhea. In addition, abdominal pain, small-spot rash, weakness, weight loss and headaches may occur. It is likely that the invasion of Blastocystis hominis may contribute to the development of irritable bowel syndrome.

Traveling to countries with low sanitary and hygienic standards is a factor conducive to infection. Inborn or acquired immunodeficiency are considered to contribute to the occurrence of clinical symptoms, but there is no evidence of a relationship between the degree of damage to the immune system and the occurrence of symptomatic blastocystosis. Preventive treatment of blastocystosis consists in observing basic hygiene rules, the consumption of safe (pathogen free) water and food.