It causes a watery diarrhea which is severe in immunocompromised individuals such as AIDS, cancer patients etc. Infection is acquired by ingestion of oocysts. It presents as watery diarrhea, abdominal cramps , dehydration, fever and vomiting. Oocysts can be visualised in stool by modified acid fast staining. Nuclei of sporozoites can be stained with DAPI. Immunofluorescence and ELISA can be used for the detection of antigens and antibodies. PCR is mainly used for research and epidemiological purposes.
Cryptosporidium parvum oocysts stained with modified acid-fast. Against a blue-green background, the oocysts stand out in a bright red stain. Sporozoites are visible inside the two oocysts to the right in this image.