[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Apicomplexans](https://durgical.com/en/microbiology/groups/apicomplexans/) › Cryptosporidium spp.

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

# Cryptosporidium spp.

- Parasite
- Exam priority: medium

A tiny gut parasite spread by water, even chlorinated, and by contact. It causes watery diarrhea, which can be severe in people with AIDS.

Updated 2026-11-01

Also called: Cryptosporidium hominis, Cryptosporidium parvum, crypto

## Key points

- Small acid-fast oocysts (about 4 to 6 µm).
- Chlorine-resistant: outbreaks in pools and water systems.
- Self-limited watery diarrhea in healthy people; chronic and severe in AIDS with low CD4.
- Oocysts infectious when passed; autoinfection.
- Nitazoxanide; in HIV, antiretrovirals.

## At a glance

**Shape**
Round oocyst with four sporozoites

**Family**
Cryptosporidiidae

**Type**
Apicomplexan protozoan (coccidian), intracellular but extracytoplasmic

**Stain**
Modified acid-fast: red oocysts on a blue-green background

**Size**
Oocyst about 4 to 6 µm

## Morphology

- Small round oocysts, acid-fast on the modified stain.
- On biopsy they appear as dots along the epithelial brush border.
- Trichrome does not stain them well.

## Transmission

- Drinking or recreational water contaminated with feces; oocysts tolerate chlorine.
- Person-to-person (daycare) and contact with calves and other animals.
- Contaminated raw food.
- Contact precautions for diapered or incontinent patients.

**Reservoir:** Humans (C. hominis); Cattle, especially calves (C. parvum)

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- Sporulated oocysts are swallowed; they are infective as soon as they are passed.
- In the small intestine they release sporozoites that invade the surface of epithelial cells.
- They multiply asexually and then sexually inside a vacuole beneath the cell membrane.
- Thin-walled oocysts form and reinfect the same host (autoinfection).
- Thick-walled oocysts leave in feces and are immediately infectious.

## Virulence factors

- Intracellular but extracytoplasmic location, protected under the membrane.
- Autoinfection by thin-walled oocysts: persistent infection in immunodeficiency.
- Chlorine-resistant oocysts and a low infectious dose.
- Villus atrophy and secretory diarrhea.

## Diseases it causes

- Cryptosporidiosis: watery diarrhea lasting one to two weeks in immunocompetent people. [Cryptosporidiosis and other intestinal coccidia (Cyclospora, Cystoisospora) →](https://durgical.com/en/conditions/cryptosporidiosis-and-other-intestinal-coccidia/)
- Acute gastroenteritis in children and outbreaks from water or pools. [Acute (viral) gastroenteritis →](https://durgical.com/en/conditions/acute-gastroenteritis/)
- Severe chronic diarrhea and wasting in people with HIV and low CD4; it can involve the biliary tree. [HIV infection and AIDS →](https://durgical.com/en/conditions/hiv-infection-and-aids/)

## Clinical picture

- Profuse watery diarrhea, cramps, nausea and low fever.
- Immunocompetent: resolves on its own within 1 to 3 weeks.
- AIDS: chronic diarrhea with dehydration, malabsorption and cholangitis.

## Diagnosis

- Modified acid-fast (Kinyoun) stain of stool.
- Stool antigen (immunoassay, rapid tests) or direct immunofluorescence.
- PCR in gastrointestinal panels.
- It must be requested specifically: a routine ova-and-parasite exam often does not look for it.

## Treatment

Rehydration is the basis. Nitazoxanide is the approved antiparasitic for immunocompetent patients. In people with HIV, what helps most is antiretroviral therapy that restores CD4 counts.

Drug class only; doses and regimens are set by the clinician from the current guideline.

## Prevention

- Boiled or filtered water; pool chlorine does not kill it quickly.
- No swimming in pools while ill with diarrhea and for two weeks afterward.
- Handwashing with soap and water (alcohol gel does not work well against oocysts).
- People with HIV: avoiding untreated water and contact with calves.

**Vaccine:** There is no vaccine.

## In Colombia

It is an important cause of diarrhea in young children and people with HIV in Colombia; many labs report it only when the modified acid-fast stain is requested.

## Memory aid

«Crypto: tiny, red and chlorine-proof»: the smallest coccidian turns red on acid-fast stain and shrugs off pool chlorine.

## Test yourself

Think of the answer, then tap the question to see it.

## Which stain is used to see Cryptosporidium in stool?

The modified acid-fast (Kinyoun) stain, which shows red oocysts on a blue-green background.

## Why does Cryptosporidium cause outbreaks in chlorinated pools?

Because its oocysts tolerate usual chlorine levels and the infectious dose is low.

## How does cryptosporidiosis present in a patient with AIDS and very low CD4?

As chronic watery diarrhea with dehydration, wasting and sometimes cholangitis; it improves when antiretrovirals restore immunity.

## Which antiparasitic is approved for cryptosporidiosis?

Nitazoxanide, together with rehydration.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/cryptosporidium-spp/)

## Related

- [Cyclospora cayetanensis and Cystoisospora belli](https://durgical.com/en/microbiology/cyclospora-cayetanensis-and-cystoisospora-belli/)
- [Giardia duodenalis](https://durgical.com/en/microbiology/giardia-duodenalis/)
- [Toxoplasma gondii](https://durgical.com/en/microbiology/toxoplasma-gondii/)

## Related conditions

- [Cryptosporidiosis and other intestinal coccidia (Cyclospora, Cystoisospora)](https://durgical.com/en/conditions/cryptosporidiosis-and-other-intestinal-coccidia/)
- [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 - Cryptosporidiosis](https://www.cdc.gov/dpdx/cryptosporidiosis/index.html) (CDC, 2024); [About Crypto Infections | Cryptosporidium ("Crypto") | CDC](https://www.cdc.gov/cryptosporidium/about/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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