Cryptosporidiosis is caused by the intracelullar intestinal protists from genus Cryptosporidium and phyllum Apicomplexa. C. parvum and C. hominis are the most common cryptosporidia in humans.
They are causing diarrhea that is especially dengerous in immunocompromised pacients including that with AIDS. Other human protozoal intestinal parasites include Isospora belli, Cyclospora cayetanensis, Balantidium coli and Dientamoeba fragilis.