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[Microbiology](https://durgical.com/en/microbiology/) · [Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/)

# Cyclospora cayetanensis and Cystoisospora belli

- Parasite
- 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

## Key points

- Cyclospora: oocysts about 8 to 10 µm, variably acid-fast and autofluorescent; outbreaks from fresh produce.
- Cystoisospora: large ellipsoid oocyst; diarrhea in AIDS; can cause eosinophilia.
- No direct person-to-person spread: the oocyst must mature outside the body.
- Treatment for both: trimethoprim-sulfamethoxazole.

## 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 →](https://durgical.com/en/conditions/acute-gastroenteritis/)
- Chronic diarrhea in people with advanced HIV from Cystoisospora or Cyclospora. [HIV infection and AIDS →](https://durgical.com/en/conditions/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.

## In Colombia

Both coccidia are described in Colombia, mostly in children with diarrhea and in people with HIV. They are found by requesting a modified acid-fast stain on the stool exam.

## Memory aid

«Small, medium, large»: Crypto, Cyclo, Cysto. The last two share the same cure pair: trimethoprim and sulfa.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/cyclospora-cayetanensis-and-cystoisospora-belli/)

## Related

- [Cryptosporidium spp.](https://durgical.com/en/microbiology/cryptosporidium-spp/)
- [Toxoplasma gondii](https://durgical.com/en/microbiology/toxoplasma-gondii/)

## Related conditions

- [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/)
- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Apicomplexans](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/dpdx/cyclosporiasis/index.html) (CDC, 2024); [CDC - DPDx - Cystoisosporiasis](https://www.cdc.gov/dpdx/cystoisosporiasis/index.html) (CDC, 2024); [Clinical Care of Cyclosporiasis | Cyclosporiasis | CDC](https://www.cdc.gov/cyclosporiasis/hcp/clinical-care/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/cyclospora-cayetanensis-and-cystoisospora-belli/