Cyclospora cayetanensis and Cystoisospora belli !
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- Exam priority: medium
Two intestinal coccidia that cause long-lasting watery diarrhea; Cyclospora comes with fresh produce and Cystoisospora mostly affects immunocompromised people.
Updated 2026-11-01
Also called: Isospora belli (old name), cyclospora
At a glance
- Shape
- Cyclospora: round oocyst; Cystoisospora: large ellipsoid oocyst
- Family
- Eimeriidae (Cyclospora) and Sarcocystidae (Cystoisospora)
- Type
- Intestinal apicomplexan protozoa (coccidia)
- Stain
- Modified acid-fast (variable for Cyclospora); both autofluoresce under ultraviolet light
- Size
- Cyclospora about 8 to 10 µm; Cystoisospora about 25 to 30 µm
Morphology
- Cyclospora: medium-sized round oocysts with variable acid-fast staining (some red, some pale).
- Cystoisospora: large oval oocysts with one or two sporoblasts.
- Both give blue autofluorescence under ultraviolet light.
Transmission
- Swallowing sporulated oocysts in contaminated water or food (berries, fresh herbs, lettuce for Cyclospora).
- Not spread directly from person to person: freshly passed oocysts are not infective.
Reservoir: Humans (the only known host of both species)
Isolation precautions
What the care team adds to standard precautions.
- Standard
Life cycle
- Oocysts are passed unsporulated in feces and are not infective at first.
- In the environment they mature over days to weeks (Cyclospora needs warmth and moisture).
- Sporulated oocysts are swallowed with water or food.
- They release sporozoites that invade small-intestine epithelium and multiply.
- After a sexual phase, new oocysts form and leave in the feces.
Virulence factors
- Invasion of small-bowel epithelium with villus blunting.
- Secretory diarrhea and malabsorption.
- Cystoisospora can cause eosinophilia, unusual for protozoan infections.
Diseases it causes
- Prolonged and relapsing watery diarrhea (cyclosporiasis, cystoisosporiasis), with fatigue and weight loss. Acute (viral) gastroenteritis →
- Chronic diarrhea in people with advanced HIV from Cystoisospora or Cyclospora. HIV infection and AIDS →
Clinical picture
- Watery diarrhea with cramps, nausea, anorexia and marked fatigue; may last weeks and relapse.
- Outbreaks from imported fresh produce (Cyclospora).
- In immunocompromised people: chronic diarrhea with wasting.
Diagnosis
- Stool exam with modified acid-fast or modified safranin stain.
- Fluorescence microscopy: oocysts glow without any stain.
- PCR in gastrointestinal panels.
- Size separates the coccidia: Cryptosporidium small, Cyclospora medium, Cystoisospora large.
Treatment
Trimethoprim-sulfamethoxazole is the treatment of choice for both; people with HIV may need longer therapy or chronic suppression. Metronidazole and albendazole do not work against Cyclospora.
Drug class only; doses and regimens are set by the clinician from the current guideline.
Prevention
- Careful washing of fresh fruit and herbs (though it does not always remove oocysts).
- Safe water and sanitation.
- In people with HIV, trimethoprim-sulfamethoxazole prophylaxis also reduces cystoisosporiasis.
Vaccine: There is no vaccine.
Test yourself
Think of the answer, then tap the question to see it.
Why is Cyclospora not spread directly from person to person?
Because its oocysts are passed unsporulated and need days to weeks in the environment to become infective.
Which intestinal coccidian can cause eosinophilia?
Cystoisospora belli, unlike most intestinal protozoa.
What is the treatment of choice for cyclosporiasis?
Trimethoprim-sulfamethoxazole; metronidazole and albendazole do not work.
How are Cryptosporidium, Cyclospora and Cystoisospora told apart on acid-fast stain?
By size: Cryptosporidium is the smallest, Cyclospora is intermediate and Cystoisospora is large and ellipsoid.
Related
Related conditions
← Back to the group: Apicomplexans
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: CDC - DPDx - Cyclosporiasis (CDC, 2024); CDC - DPDx - Cystoisosporiasis (CDC, 2024); Clinical Care of Cyclosporiasis | Cyclosporiasis | CDC (CDC, 2024).
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