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Understanding Intestinal Spore-Forming Protozoa: Cryptosporidia, Microsporidia, Isospora, and Cyclospora

Richard W. Goodgame, MD
[+] Article and Author Information

From Baylor College of Medicine and Ben Taub General Hospital, Houston, Texas. Acknowledgments: The author thanks Drs. Linda Rabeneck, Wayne Shandera, and Cynthia Chappell for critiques of the manuscript. Credit for the photomicrographs goes to Dr. Robert Genta (Figure 2 and Figure 3, left), Dr. Charles Stager (Figure 3, right), Professor Sebastian Lucas (Figure 4, left), and Dr. P.L. Chiodini (Figure 4, right, and Figure 5). Requests for Reprints: Richard W. Goodgame, MD, Baylor College of Medicine, One Baylor Plaza, Room 525-D, Houston, TX 77030.


Copyright ©2004 by the American College of Physicians


Ann Intern Med. 1996;124(4):429-441. doi:10.7326/0003-4819-124-4-199602150-00008
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Objectives: To summarize recent information about the “new” gastrointestinal protozoal pathogens (cryptosporidia, microsporidia, isospora, and cyclospora) and to help practicing clinicians integrate this information into their clinical databases by emphasizing the similarities among these organisms.

Data Sources: Relevant English-language articles published between 1988 and 1995 were identified through a MEDLINE search done using the names of the intestinal spore-forming protozoa. Articles cited in the bibliographies of these and other articles were searched manually.

Study Selection: Studies that contained information on the history, taxonomy, life cycle, epidemiology, pathogenesis, clinical manifestations, diagnosis, and treatment of the pathogens were reviewed.

Data Extraction: Cryptosporidium parvum, Isospora belli, Cyclospora cayetanensis, Enterocytozoon bieneusi, and Septata intestinalis are intestinal spore-forming protozoa that cause intracellular infections, predominantly in the epithelial cells of the intestine. They are transmitted either by stool from person to person or through contaminated water or food by an infectious particle called a spore or oocyst. Asymptomatic infections occur; the most common symptom of infection is diarrhea. Infections have been associated with intestinal inflammation, disordered architecture (such as villus blunting), and abnormal function (for example, malabsorption). Mild to moderate, self-limited diarrhea is common in healthy persons, but patients with immune dysfunction can have severe intestinal injury and prolonged diarrhea. Diagnosis is made by a microscopic examination of the stool and the use of appropriate staining techniques. Effective antibiotic treatment for prolonged infection in immunocompromised patients is available for most of these infections.

Conclusions: The intestinal spore-forming protozoa are four frequently identified gastrointestinal pathogens that have important similarities in epidemiology, disease pathogenesis, clinical manifestations, diagnosis, and treatment.

Figures

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Figure 1.
A small-intestinal villus infected with all four intestinal spore-forming protozoa.

All four organisms mature and multiply intracellularly in enterocytes, and all produce an infectious particle (spore or oocyst) that is excreted in the stool. However, the organisms vary in size and intracellular location.

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Figure 2.
Cryptosporidium parvum.Left.Right.

As seen in jejunal biopsy specimen (hematoxylin and eosin stain; original magnification, × 400). As seen in the feces (modified acid-fast stain; original magnification, × 1000). Actual size, 4 to 6µm

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Figure 3.
Enterocytozoon bieneusi.Left.Right.

As seen in jejunal biopsy specimen as irregular oval bodies in the apical cytoplasm of most of the enterocytes (hematoxylin and eosin stain; original magnification, × 400). As seen in the feces as red-pink oval spores mixed among blue bacteria (modified trichrome stain; original magnification, × 1000). Actual size, 1µm

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Figure 4.
Isospora belli.Left.Right.

As seen in jejunal biopsy specimen as large, densely staining, oval bodies in the apical cytoplasm of three enterocytes surrounded by an artifactual clear space (hematoxylin and eosin stain; original magnification, × 400). As seen in feces (modified acid-fast stain; original magnification, × 1000). Actual size, 25µm

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Figure 5.
Cyclospora cayetanensis.Left.C. cayetanensisRight.Cyclospora

Transmission electron photomicrograph of jejunal biopsy specimen showing six merozoites of within an enterocyte. oocyst in feces (modified acid-fast stain; original magnification, × 1000). Actual size, 8µm

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