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cryptosporidiosis

Friday 15 April 2005

Epidemiology

About one or two cases of cryptosporidiosis per 100,000 people are reported annually in the United States.

Typically, cryptosporidium is an acute, short-term infection characterized by diarrhea. However, protracted diarrhea can occur in children and immunocomprimised hosts such as AIDS patients.

A few incidences of outbreak due to contaminated drinking water and food had occurred in the United States and developed countries recently.

In 2006, an outbreak in the United States involved 6 states and was attributed to the use of public recreational water. Cryptosporidiosis outbreak can also occur in animals which can infect the human care-givers.

The complete genomes of Cryptosporidium parvum and Cryptosporidium hominis have been entirely sequenced.

Unlike other eukaryotes, these two species have simplified mitochondria and Cryptosporidium parvum does not contain mitochondrial DNA.

The genomic data can be assessed through the NIH funded database (CryptoDB.org) at http://www.cryptodb.org/. Cryptosporidium canis, Cryptosporidium felis, Cryptosporidium meleagridis, and Cryptosporidium muris can also cause disease in humans.

Pathology

Endoscopic findings can vary from normal to mild changes such as mild erythema, mucoal granularity, mucosal atrophy, and mild erosion.

Although Cryptosporidium can be found throughout the entire gastrointestinal tract, they are most commonly found in the small intestine and biopsy of the small intestine is a rather sensitive diagnostic method

Histologically, two salient features for diagnosis of Cryptosporidium parvum are the characteristic 2 to 5 μm, mostly extracellular, basophilic bead-like spherical bodies that typically line the surface of the intestinal epithelial cells.

Cryptosporidium can be found on the surface or the crypts of the small intestine. Giemsa stain is helpful in highlighting these organisms.

The mucosa may have other changes including mixed acute and chronic inflammatory cell infiltration, crypt abscess formation, villous atrophy and crypt hyperplasia.

With a high index of suspicion and knowing the clinical history, Cryptosporidium can be picked up easily on medium (10X) magnification and confirmed on higher magnification. Confirmation by immunohistochemistry is helpful.

Differential diagnosis

The major differential diagnoses include other coccidial infections. These microorganisms are all small organisms that can be recognized under the microscope, with microsporidia being the most difficult to recognize using hematoxylin and eosin stain.

Electron microscopy has played an important role in the past for confirmation of the diagnosis.

Immunohistochemistry, ELISA, and PCR help making a faster diagnosis.

- Cyclospora cayetanensis
- Microsporidia (Enterocytozoon bieneusi, Encephalitozoon intestinalis)
- Isospora belli

Phylum Apicomplexa

Cryptosporidium belongs to Phylum Apicomplexa.

Other human pathogens in Phylum Apicomplexa include Plasmodium sp. and Toxoplasma sp.

In contrast to Plasmodium and Toxoplasma, Cryptosporidium sp. can complete its entire life cycle within a single host such as human. The oocysts are excreted in feces and new hosts are infected by fecal oral contamination or through contaminated water or food.

Unlike bacteria, Cryptosporidial oocysts are resistant to chlorine disinfection and can survive for days in contaminated fresh water. This fact contributes, most likely, to the 2006 outbreak in the United States.

Localization

- digestive cryptosporidiosis

  • gastric cryptosporidiosis
  • intestinal cryptosporidiosis

- biliary cryptosporidiosis

Predisposing factors

- immunodeficiencies

  • AIDS

References

- Chen XM, Keithly JS, Paya CV, LaRusso NF. Cryptosporidiosis.
N Engl J Med. 2002 May 30;346(22):1723-31. PMID: #12037153#