Cryptosporidium spp. table


A 34-year old Hispanic man with a history of HIV infection is admitted to the hospital.  His CD4 cell count is 18 (a normal count is from 500-1200), and he complains of pain in the upper right abdomen, nausea, fever and vomiting.  What opportunistic infection has taken hold in his body?  How can it be diagnosed?  Can anything be done for him?  (see below for answers!)


Life Cycle          Cryptosporidiosis and HIV/AIDS           Glossary         References and Links


What is it?

Cryptosporidiosis, or “crypto,” is an enteric disease caused by a protozoa.  Crypto is found all over the world.  Prevalence rates in Europe and North America range from 1-6%, while rates in Asia and Africa are as high as 20%.  It can affect both humans and animals (crypto infections have been found in up to 150 different species), mainly causing watery diarrhea.  Other symptoms include abdominal pain, and sometimes fever, malaise, nausea, vomiting, and loss of appetite.  Symptoms usually occur two to ten days after infection, but it is important to note that many crypto infections may be asymptomatic.  The most common animal reservoir is cattle, although crypto has been detected in reptiles, birds, and insects.

Picture from Medical Journal of Australia website


Is it serious?

Although crypto is usually cleared by the immune system, it can be life-threatening for people suffering from severe immunodeficiencies, such as AIDS.  It also disproportionately affects children from underdeveloped countries.  Chronic crypto infection has been linked with impairments in physical fitness and reduced cognitive abilities.  Sadly, children with persistant diarrhea enter a vicious cycle of malnutrition of decreased nutritional status and further diarrheal illnesses.


How is it transmitted?

Crypto is normally a zoonotic infection spread by contaminated water, although food-borne and person-to-person infections have been documented.  Many outbreaks can be traced to water run-off carrying animal waste.  Endemic transmission usually occurs through contamination of public water sources, such as beaches and pools.  It is only in large outbreaks that contamination of the drinking water supply has been implicated.  Food-borne transmission has only been reliable documented in one case.  Person-to-person transmission is much more frequent, often occurring in nursing homes and day care centers.  Crypto has a very low infectious dose (amount needed to establish infection in the host), ranging from 9 to 1000 oocysts, depending on the species of parasite. 


How does a doctor diagnose an infection?

The most widely used diagnostic test is the modified acid-fast or Kinyoun stain.  It is used to detect Cryptosporidium in stool samples.  Several immunofluorescent assays are also available, which test for antibodies to the parasite in the blood.  Some pharmaceutical companies have produced rapid-result commercial assays, which are moderately successful (~75% detection rate).  Polymerase chain reaction (PCR) techniques might also prove to be effective in diagnosing infection.

Picture from Johns Hopkins website

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Why is it a threat to public health?

Crypto is a serious issue for two reasons:  current water purification methods are ineffective at removing the parasite from drinking water, and there is no effective therapy to treat cryptosporidium infection. 


How can transmission be prevented?

People should wash their hands regularly as the most effective means of preventing transmission.  Immunocompromised individuals should peel, wash, and cook all vegetables thoroughly.  They may also wish to boil or filter drinking water.


And what about our sick patient?

This man has a cryptosporidium infection which will be diagnosed by one of the assays mentioned above.  His doctor will attempt to reconstitute his immune system with a HAART regimen, which will hopefully clear the parasite from his system.  Otherwise, only supportive care to replenish lost fluids and to prevent wasting is available.



1976—The first two human cases of cryptosporidiosis are reported.

1984—The first reported waterborne outbreak of crypto is attributed to fecal contamination of a public artesian well in Texas.

1993—A crypto outbreak in Milwaukee, Wisconsin sickens 400,000 people and causes over 100 deaths.  It is traced to a contaminated water supply.

1996—A food-bourne outbreak occurs in the Northeast U.S.  It is determined that unpasteurized apple cider was contaminated during processing.


Created by:  Rebecca Hammon

                    Stanford University

                    May 2003