C.parvum is inactivated by heat, freezing and drying, so heat-treated, frozen and dried foods should be safe unless contaminated after processing. In humans it causes cryptosporidiosis, an intestinal infection. Older animals may be carriers. The organism was discovered early in the twentieth century but its importance was only realised in the 1970s by veterinary workers investigating the causes of scours in young farm animals. Many of the early human cases were noted in the 1980s as serious infections in severely immunocompromised patients including AIDS sufferers Now widely recognised as an enteric pathogen with a world-wide distribution, it is endemic in some areas.
Infection rates are highest in developing countries and in children.
Many animal species can be infected and C.parvum is readily passed from animals to humans. An incubation period of 2-14 days follows ingestion of oocysts. Very low doses are able to initiate an infection, probably less than 100 oocysts. The illness is characterised by a profuse watery diarrhoea with abdominal pain. It can also cause vomiting, weight loss, loss of appetite and a low grade fever.