Cryptosporidiosis in humans is caused primarily by two species, Cryptosporidium parvum and C. hominis. There are annually approximately 1.4 cases/100,000 in the United States reported to the Centers for Disease Control. Infection results from ingestion of fecally contaminated water or food containing the infectious oocyst form. Sporozoites are released from the oocyst in the small intestine and attach to the epithelial cell surface. Upon invasion of the epithelial cells the parasite undergoes both the sexual and asexual stages of the life cycle. Infection with C. parvum in a normal host leads to days to several weeks of non-bloody diarrhea.