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.
Top Row: Immature oocysts
Bottom Row, Calcofluor White, MAF
Mature oocyst, wet mount
Mature oocyst, MAF
MAF = Modified Acid-Fast Stain (1% Acid Rinse)
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
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.
Extraintestinal: Biopsy specimens, routine histology
Intestinal: Concentration sediment wet preparation; modified acid-fast stains, calcofluor white, auramine-rhodamine
Extraintestinal: Routine histology
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
Cystoisospora (Isospora) belli oocysts
Garcia, L.S. 2007. Diagnostic Medical Parasitology, 5th ed., ASM Press, Washington, D.C.
Improved hygiene, adequate disposal of fecal waste, adequate washing of contaminated fruits and vegetables