Cryptosporidium is a microscopic protozoan parasite that is a significant cause of diarrheal disease (cryptosporidiosis) in humans and animals, including ruminants, swine, cats, and dogs. The word cryptosporidium means hidden spore, referring to the ease with which it can escape detection in environmental samples. Most cryptosporidiosis appears to be caused by the species Cryptosporidium parvum. The dormant and resistant forms of Cryptosporidium, referred to as oocysts, are excreted in the feces of infected humans and animals and can survive under a wide range of environmental conditions. Cryptosporidiosis had long been recognized as a veterinary problem, especially in young farm animals, but was only recognized as a cause of human disease in 1976, when it was diagnosed in animal handlers.

The most common symptom of cryptosporidiosis is watery diarrhea. Other symptoms may include abdominal cramps, nausea, low-grade fever, dehydration, and weight loss. Symptoms usually develop four to six days after...