Cryptosporidium is an important cause of inflammatory bowel disease in humans and other animals. The oocyst stage of the parasitic organism can remain infective under cool, moist conditions for many months, especially where water temperatures in rivers, lakes, and ponds remain low but above freezing. Numerous reports of outbreaks of cryptosporidiosis related to drinking water in North America, the UK, and Japan, where detection methods are in place, indicate that water is a major vehicle for transmission of cryptosporidiosis. The chlorine-resistant tiny oocysts may contaminate drinking and recreational water, food, day care centers, hospitals, and persons with exposure to animals or unsanitary conditions.
Cryptosporidium wrairi is a major protozoan parasite in the guinea pig, house mouse and chickens. Intestinal overgrowth of this organism may cause weight loss in adults and diarrhea and/or poor growth rates in weanlings and juveniles. Other species of Cryptosporidium are infectious to domestic cats, turkey and fish. Recent studies proved that Cryptosporidium felis is also infectious to humans and cattle.
Cryptosporidiosis is a cause of disease and mortality in animals and humans, resulting primarily in diarrhea, and causing the most severe infections in immune-compromised individuals. Of 15 named species of Cryptosporidium infectious for nonhuman animal hosts C. baileyi, C. canis, C. felis, . hominis, C. meleagridis, C. muris, and C. parvum have been reported to also infect humans. Humans are the primary hosts for C. hominis, and except for C. parvum, which is widespread amongst animals and is the most frequently reported zoonotic species, the remaining species have been reported primarily in people with weakened immune system. Studies suggest that Cryptosporidium hominis is spread only between humans. Outbreaks of clinical disease can be partially controlled by the addition of 0.2% sulfamethazine to the water supply.