Phylum- Apicomplexa

Order – Eimeriida

Genus – Cryptosporidium

Species – C. parvum

Cryptosporidiosis (or “Crypto” for short) is a disease that causes watery diarrhea. It is caused by microscopic parasite Cryptosporidium parvum. Ingestion of sporulated oocyst of the parasite through contaminated food and water causes transmission of parasite into a host body. The sporulated oocyst are colorless, transparent, oval or spherical-shaped, with 4 crescent – shaped sporozoites in it. They reside in the small intestine.

Habitat and geographical distribution

C. parvum are intracellular parasite, found within the micro-villion region of epithelial tissue of small intestine. Cryptosporidiosis is found worldwide.

Life cycle of C. parvum

Sporulated oocysts, containing 4 sporozoites, are excreted by the infected host through feces and possibly other routes such as respiratory secretions. Transmission of Cryptosporidium parvum occurs mainly through contact with contaminated water (e.g., drinking or recreational water) and food. Following ingestion by a suitable host, excystationoccurs. The sporozoites are released and parasitize epithelial cells of the gastrointestinal tract or other tissues such as the respiratory tract. In these cells, the parasites undergo asexual multiplication (schizogony)and then sexual multiplication (gametogony), producing microgamonts (male) and macrogamonts (female). Upon fertilization of the macrogamonts by the microgametes, oocysts develop that sporulate in the infected host. Two different types of oocysts are produced, the thick-walled, which is commonly excreted from the host, and the thin-walled oocyst, which is primarily involved in autoinfection. This way life cycle continues.

Clinical manifestation of cryptosporidiosis

Symptoms of cryptosporidiosis generally begin 2 to 10 days (average 7 days) after becoming infected with the parasite (incubation period). The most common symptom of cryptosporidiosis is watery diarrhea. Symptoms include:

  • Watery diarrhea
  • Stomach cramps or pain
  • Dehydration
  • Nausea
  • Vomiting
  • Fever
  • Weight loss

Some people with Crypto will have no symptoms at all.

Symptoms usually last about 1 to 2 weeks in persons with healthy immune systems.While the small intestine is the site most commonly affected, in immunocompromised persons Cryptosporidium infections could possibly affect other areas of the digestive tract or the respiratory tract.

People with weakened immune systems may develop serious, chronic, and sometimes fatal illness. Examples of people with weakened immune systems include:

  • people with HIV/AIDS;
  • those with inherited diseases that affect the immune system; and
  • cancer and transplant patients who are taking certain immunosuppressive drugs.

Laboratory diagnosis

i. Microscopy-

a. atleast 3 stool samples are to be examined to confirm the oocyst of cryptosporidia;

Formalin ethyl- acetate sedimentation technique (with low speed centrifugation) is used to concentrate stool specimen for proper visibility of oocysts.

b. wet mount examination with iodine solution, of various stool samples are done

c. Acid-fast staining of sample shows oocyst stained red with safranin 

ii. Enzyme immunoassays for cryptosporidial antigen detection (EIA, Immunofluorescence microscopy)

iii. PCR

Treatment, prevention and control

  • Most people who have healthy immune systems will recover without treatment. Diarrhea can be managed by drinking plenty of fluids to prevent dehydration
  • Anti-diarrheal medicine may help slow down diarrhea, but a healthcare provider should be consulted before such medicine is taken. Nitazoxanide can help reduce diarrhea
  • use of chlorine disinfection and boiling is a reliable method to control Cryptosporidium in drinking water. Ultraviolet light treatment at relatively low doses will inactivate Cryptosporidium
  • People with cryptosporidiosis should not swim in communal areas because the pathogen can reside in the anal and genital areas and be washed off. They should wait until at least two weeks after diarrhea stops before entering public water sources, since oocysts can still be shed for a while.

Binod G C

I'm Binod G C (MSc), a PhD candidate in cell and molecular biology who works as a biology educator and enjoys scientific blogging. My proclivity for blogging is intended to make notes and study materials more accessible to students.