Life Cycle

Cryptosporidiosis is a parasitic infection caused by Cryptosporidium parvum. Once a person is infected by the protozoan, the parasite resides in the intestine and then is passed into the stool of the infected person. "Crypto" as the parasite and disease are commonly known as, is a diarrheal disease; symptoms include watery diarrhea, dehydration, cramps and nausea.

Crypto has gained particularly notoriety during the past two decades as it has become one of the most common causes of waterborne diseases in the United States. It is spread easily by contaminated food and water thus making cleanliness vitally important in its prevention and control.

Cryptosporidium was first recognized as a cause of disease in 1976. As methods were developed to analyze stool samples, the protozoa was increasingly reported as the cause of human disease. Crypto was first categorized as a veterinary problem because the majority of the early cases were diagnosed in handlers of such farm animals as cows. 155 species of mammals have been reported to be infected wity Cryptosporidium parvum or C. parvum. Of 15 named species of Cryptosporidium infectious to nonhuman vertebrate hosts C. Baileyi, C. canis, C. felis, C. hominis, C meleagridis, C. muris, and C. parvum have been reported to also infect humans. Humans are the primary hosts for C. hominis, and except for C. parvum, which is widespread in nonhuman hosts and is the most frequently reported zoonotic species, the remaining species have been reported primarily in immunocrompomised humans.

The first widely publicized outbreak of Crytpsporidiosis occurred in 1987 in Carrollton, Georgia, where approximately 13000 people became ill with the disease. The source of the outbreak was traced to a contaminated municipal water system. Six years later, in Milwaukee, Wisconsin, drinking water was again contaminated, causing approximately 400000 people to become ill.

Life Cycle:

Following ingestion (3) or inhalation, excystation occurs which allows the released sporozoites to parasitize epithelial cells (b,c) of the intestines. In these epithelial cells the parasite undergoes asexual expansion (d,e,f) and then sexual reproduction producing microgamonts (male, g) and macrogamonts (female, h). Upon fertilization (i), oocysts form (j,k) that are then able to sporulate in the host. Thick-walled oocysts (j,k) are excreted from the host while thin-walled oocysts (k) are then often involved in autoinfection.


Image courtesy of CDC.

Cryptosporidium lives in the intestines of infected individuals and is released with bowel movements. Because the parasite is passed with the stool of an effected individual, any surfaces that may come in contact with human or animal feces is suspect to Crypto contamination. A person must ingest the parasite to become infected but, interestingly, cannot be infected through the contact of blood.

Commons modes of transmission include:
1. Eating uncooked foods contaminated with the parasite.
2. Swallowing something that has come in contact with human or animal feces.
3. Swallowing pool water that has been contaminated with the parasite. (Cryptosporidium parvum is able to survive for several days in mild chlorine.)

Infected individuals can spread the disease very easily if they are not careful about their hygiene. For that matter, frequent handwashing is the most important thing people can do to avoid spreading crypto.

Crypto oocysts, shown above, can be spread by physical contact. (Image courtesy of the San Francisco PUC)

The most common symptom of the disease is watery diarrhea.
Other symptoms usually include:
1. Abdominal cramps
2. Nausea
3. low-grade fever
4. Dehydration
5. Weight loss

Interestingly, some people will have absolutely no symptoms at all.


A doctor is unable to diagnose Crypto from symptoms alone. Instead, stool samples must be submitted for laboratory analysis. Common laboratory diagnostic methods of cryptosporidiosis include microscopy, enzyme immunoassays and molecular biology methods.

Oocysts of C. parvum labeled with immunofluorescent antibodies

Image courtesy of CDC. Oocysts can be detected with fluorescent antibodies.


PCR diagnostic test

Image courtesy of CDC. Diagnostics can involve PCR detection of C. parvum in stool specimen

To date, there is no established specific treatment of patients with cryptosporidiosis. One drug, nitazoxanide, however, has been approved by the FDA for treatment of immunocompetent patients. For patients with compromised immune systems, such as HIV/AIDS patients, anti-retroviral therapy, which has been shown to reduce oocyst excretion, is recommended.

Because diarrhea results in the rapid loss of fluids, it is also recommended that patients drink plenty of fluids to prevent dehydration. Antidiarrheal medicine may help slow down fluid loss.

Effective prevention involves practicing good hygiene. Individuals with compromised immune systems should take particular care to avoid contact or exposure with Cryptosporidium. To minimize the chances of infection:
1. Wash your hands thoroughly with soap and water
a. After using bathroom
b. After handling animals
c. After touching dirt
d. Before preparing food
2. Avoid drinking untreated water
3. Peel and rinse fruits and vegetables
4. Follow water advisories

Cryptosporidium-free water
Possibly contaminated with Cryptosporidium
Reverse Osmosis Treated Carbon-filtered
Distilled Particle-filtered
1 micron, or smaller, filtered UV light treated
  Activated-carbon treated
Spring water
Well water

Oocysts are able to survive for several days in mildly chlorinated water.(Image courtesy of San Francisco Department of Health)


Fayer, R. Cryptosporidium: a water-borne zoonotic parasite. Veterinary Parasitology. (2004) 126:37-56.

Xiao, L.and Ryan, UM. Crytpsporidiosis: an update in molecular epidemiology. Curr Opin Infec Dis. (2004) 5:483-490.

Smith, HD, and Corcoran, GD. New drugs and treatment for cryptosporidiosis. Cur Opin Infec Dis. (2004) 6:557-564.

San Francisco Public Utilities Commission."Cryptosporidium White Sheet" Available online at:

San Francisco Department of Public Health - Environmental Health Section. Cryptosporidium Surveillance Project. Available online at: ehs/phes/water/crypto.htm

Centers for Disease Control and Prevention: Division of Parasitic Diseases. “Cryptosporidiosis Control and Prevention.” Available online at: