Infected animals suffer acute gastroenteritis and diarrhoea, which normally lasts several days. Individuals with compromised immune response, however, can suffer prolonged infection and cases resulting in mortality are commonplace. There is currently no known therapy.

The infected animals excrete oocysts in their faeces, which can survive considerable periods outside their hosts. Transmission is by ingestion of the oocysts. This makes cryptosporidium a significant water and food borne pathogen.

Control focuses on eliminating oocysts in water supplies. Two species, C. hominis and C. parvum, which differ in host range, genotype and pathogenicity, are most relevant to humans. C. hominis is restricted to humans, whereas C. parvum also infects other mammals.