Isospora belli
- Described by Virchow in 1860
- Named by Wenyen in 1923
Laboratory test
Stool examination 
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Staining: modified Ziehl- Neelsen (ZN) stain or Kikoyoun acid fast staining of stool smear
Duodenal aspirate examination or entero test to demonstrate oocyst
Intestinal biopsy - demonstrate oocyst 
life cycle
Man get infected through ingestion of food containing sporulated oocyst
I.belli completes life cycle in one host
When sporulated oocyst is swallowed 8 sporozoites are released from 2 sporocysts in small intestine
Incubation period 1-4 days
In epithelium sporozoites transform into trophozoites asexually multiply to produce number of merozoites
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Zygote formed after fertilization it secretes a cyst wall and develops into an immature oocyst.
Some of the trophozoites undergo sexual cycle gametogamy in the cytoplasm of enterocytes and transform into macro and microgametocytes
Morphology
- single form - oocyst
- oocyst size 20 to 30 micrometre in length and 10 to 19 micrometre breadth
- Ellipsoidal or elongated ovoid shape
- Each oocyst surrounded by a thin smooth two layered cyst wall.
- Oocyst mature outside the body.
Habitat
Large and small intestine 
Distribution
- Common in tropical and subtropical countries
- Name belli means war named associated with war during first world war
clinical features
- diarrhoea ( not bloody and self limiting)
- Abdominal discomfort, mild fever malabsorption
- Diarrhoea lasting several years for particularly HIV patients
Treatment
- immunodeficient patients treat diarrhoea with cortimoxazole .
- Patients intolerant to sulfonamides ,pyrimethamine is given.