Development of Cryptosporidium occurs more rapidly than many textbooks imply, and each generation can develop and mature in as little as 12-14 hours. Due to the rapidity of the life cycle, plus the autoinfective cycles, huge numbers of organisms can colonize the intestinal tract in several days. The ileum soon becomes crowded and secondary sites are often infected, such as the duodenum and large intestine. In immunosuppressed individuals, parasites can sometimes be found in the stomach, biliary and pancreatic ducts, and respiratory tract. Patency, which is the length of time oocysts are shed in the feces, generally lasts 6-12 days in immunocompetent individuals but may be prolonged in immunosuppressed patients.
Infections are most common in young children and immunocompromised individuals.
Symptoms of cryptosporidiosis usually appear within two to ten days after ingestion of the parasite. Symptoms include watery diarrhea, headache, abdominal cramps, nausea, vomiting and low grade fever. These symptoms may lead to weight loss and dehydration. In otherwise healthy individuals, symptoms usually last from one to two weeks, at which time the immune system is able to stop the infection. In the immunocompromised, the infection may continue and become life-threatening.