Tokyo Food Safety Information Center » Good things to know »  The microorganisms which cause food poisoning » Cryptosporidium



Cryptosporidium is a protozoan parasite belonging to the order of cossidia, which are sporozoan (parasitic spore-forming protozoan).  In 1976, it was first made clear that cryptosporidium was a cause of an infectious disease among humans, with most cases caused by Cryptosporidium parvum.
Cryptosporidium exist in the natural environment (outside a host) in the form of oocysts (thick-walled cyst zygote) and do not multiply.  If orally ingested, the oocysts multiply within the digestive tract and are then discharged in conjunction with feces, which become sources of infections to new individuals.  The parasites are resistant to chlorine disinfection with the chlorine levels commonly used in drinking water, and are reported to remain infectious.

Causing foods:

Domestic animals and mammals are reservoir hosts, and additionally, infected human patients become a transmission source of infection by discharging the oocysts through their feces.  The paths of infections include oral ingestion of contaminated foods and drinks, or contact with contaminated hands or fingers.  In an oral ingestion experiment conducted by volunteers in the United States, researchers found occurrences of infection symptoms by low exposure to some tens of oocysts.


The incubation period is two to ten days.  The main symptoms are diarrhea, stomachaches, vomiting, and fever.  Infected patients may recover in several days to two weeks.  Even if infected, some patients may show no symptoms, however, infected patients keep discharging oocysts through their feces for several weeks.
For immunodeficient patients (whose immune system's ability to fight infectious disease and cancer is compromised or entirely absent) and cancer patients having immunosuppressive therapies, the disease may persist longer, and in some cases, it is reported that the symptoms become severe.

Key points to prevention:

1. Because the oocysts, or the sources of infections, continue to be discharged, even after the symptoms get better or disappear, it is essential to sufficiently wash hands frequently to prevent secondary infections.
2. Boil drinking water for one minute at least.  Use boiled water even when you make ice.

  • When you use a water purifier, note that not all water purifiers are completely effective in removing the sources of infection. 
  • Since the sources of infection accumulate within the filter cartridge, take cautious measures including replacement of the cartridge in an appropriate manner in accordance with the water purifier instruction manual.

3. Avoid raw foods and heat/cook them before ingesting.
4. Wipe and dry tableware well.
5. If you have an infected patient within your family, have the infected person take a bath last, after other family members, to prevent spread of the infection to other family members.
6. To prevent the spread of infection through stool - soiled underwear or diapers from an infected person, douse the dirty laundry in boiled water before washing.

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