Location of cryptosporidia: review of the literature and experimental infections in calves.

Cryptosporidium, a protozoan, was present in the gastrointestinal tract of calves, lambs, goats, deer, foals, cats, rats, mice, guinea pigs, rabbits, monkeys, human beings, birds, reptiles, and fish. The usual location was the gastrointestinal tract with emphasis on the lower portion of the small intestine. In birds, cryptosporidia were also present in the respiratory tract and conjunctiva. In human beings, cryptosporidia were present in specimens from the respiratory tract. Immunologic impairment may allow a more widespread distribution of the parasite in a given animal and may be related to increased susceptibility. Experimental cryptosporidial infections in newborn calves resulted in the establishment of the organisms in jejunum, ileum, cecum, and colon. Middle and lower portions of the jejunum and ileum appeared to have the largest numbers of organisms at 5 to 7 days after inoculation, as determined by histologic examinations.