What is cryptosporidiosis?

Updated: Nov 11, 2019
  • Author: Melinda B Tanabe, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Human cryptosporidiosis is caused by infection with apicomplexan protozoans of the genus Cryptosporidium. [1, 2] Human illness was once believed to be caused by a single species, but molecular studies have demonstrated that it is caused by at least 15 different species. Among the more common species is Cryptosporidium hominis, for which humans are the only natural host, and Cryptosporidium parvum, which infects a range of mammals, including humans. [1, 2, 3] (See Etiology and Pathophysiology.)

Cryptosporidiosis mainly affects children. It causes a self-limited diarrheal illness in otherwise healthy adults. However, it is also recognized as a cause of prolonged and persistent diarrhea in children, which can result in malnutrition. [4, 5] Cryptosporidiosis can manifest as chronic severe diarrhea in persons with acquired immunodeficiency syndrome (AIDS). (See Prognosis and Presentation.)

Cryptosporidium can also cause waterborne and, less frequently, foodborne outbreaks. (See Epidemiology, Workup, and Treatment.)

The genus Cryptosporidium consists of a group of protozoan parasites within the phylum Apicomplexa. As of 2019, there were at least 35 named Cryptosporidium species, as recognized by host specificity, morphology, and molecular biology studies. [6, 7, 8] Besides humans, the parasite can infect many other species of animals, such as mammals, birds, and reptiles, and is pathogenic to immunocompetent and immunocompromised hosts (see the image below).

Modified acid-fast stain of stool shows red oocyst Modified acid-fast stain of stool shows red oocysts of Cryptosporidium parvum against the blue background of coliforms and debris.

See Common Intestinal Parasites, a Critical Images slideshow, to help make an accurate diagnosis.

Cryptosporidium species that infect humans replicate in the epithelial cell lining of the GI tract. They can complete their entire live cycle within a single host, but some species can also spread between host species. [1, 2] C hominis and C parvum cause most human infections. Both can spread person to person. C parvum can also be zoonotic.

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