Infection with Cryptosporidium species is not uncommon in horses in Canada, with a prevalence of 17% reported in a small study of horses in Alberta, Ontario, and the Yukon. Horses seem to be most commonly infected with C. parvum, which is potentially zoonotic, and also have their own distinct genotype which has also been reported very rarely as a cause of clinical disease in people. Clinical disease in horses - primarily diarrhea - is less common, and was first described in immunodeficient foals. Cryptosporidium is now recognized as a pathogen in immuno-competent foals and, less commonly, older horses. It has recently been suggested that Cryptosporidium might have a role in some cases of "foal heat diarrhea", but a link has not been conclusively established. There are no drugs approved in Canada for the treatment of cryptosporidiosis in horses.
A recent report from New Zealand described an outbreak on a thoroughbred farm. Nine foals were affected, most from four to nine days of age when diarrhea started. Two of the nine foals died and a third was euthanised because of the parasite. The Cryptosporidium involved was identified as the "cattle" genotype of C. parvum, which is potentially zoonotic. There were opportunities on the farm for across fence contacts between foals and calves, and some of the paddocks used by the horses had previously been grazed by calves.
Additional information about Cryptosporidium is available under Cattle.