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Cystoisospora (Isospora) belli (Pathogen)

This organism belongs to the coccidia, is a true pathogen, and causes isosporiasis.  The oval oocysts containing one or two immature sporonts, measure 20 to 33 by 10 to 19 µm, and are found in fecal specimens.

cysto1 cysto2 cysto3
Top Row:  Immature oocysts   
 Bottom Row, Calcofluor White, MAF

Mature oocyst, wet mount
Mature oocyst, MAF

MAF = Modified Acid-Fast Stain (1% Acid Rinse)

Life Cycle:
Intestine, oocysts passed in feces, are not infectious (require further development outside of the body), survive in the environment, and are transmitted via contaminated food and/or water.  Rare extraintestinal infections have been documented in severely immunocompromised patients.

Fecal-oral transmission via oocyst form; contaminated food and water

Worldwide, human-to-human transmission, food-borne and waterborne transmission

Clinical Features:
Intestinal: Diarrhea which last for months to years (watery, 6-10 per day), weight loss, abdominal colic, and fever. Immunosuppressed tend to have profuse diarrhea with an abnormal mucosa.
Extraintestinal:  At autopsy, microscopic findings associated with I. belli infection were seen in lymph nodes and walls of the intestine.
Chronic infections develop in some patients, and oocysts can be shed for several months to years. In one particular case, an immunocompetent individual had symptoms for 26 years and C. belli was recovered in stool a number of times over a 10‑year period.  Eosinophilia is found in many patients, recurrences are quite common, and the disease is more severe in infants and young children.

Clinical Specimen:
Intestinal:  Stool
Extraintestinal:  Biopsy specimens, routine histology

Laboratory Diagnosis:
Intestinal:  Concentration sediment wet preparation; modified acid-fast stains, calcofluor white, auramine-rhodamine
Extraintestinal:  Routine histology

Organism Description:
Oocyst:  Oval oocysts (measure 20-33 µm by 10-19 µm, containing 1 or 2 immature sporonts.  Continued development outside the body required for infectivity
Tissue:  Developing stages seen within the cells of the intestine

Laboratory Report:
Cystoisospora (Isospora) belli oocysts

Garcia, L.S. 2007.  Diagnostic Medical Parasitology, 5th ed., ASM Press, Washington, D.C.
Trimethoprim-sulfamethoxazole (TMP-SMX)

Improved hygiene, adequate disposal of fecal waste, adequate washing of contaminated fruits and vegetables