Cryptosporidiosis is a diarrheal disease caused by the parasite Cryptosporidium.


Cryptosporidiosis is a diarrheal disease caused by the microscopic parasite Cryptosporidium. Both the disease and the parasite are commonly called crypto. Since the 1970s, cryptosporidiosis has been found in the gastrointestinal or respiratory tract of most species of animals. In the United States, crypto is considered one of the most common causes of waterborne diseases.

Cryptosporidium live in the intestines of humans and animals. They are then passed onto others through the stools of the infected. In one bowel movement, millions of Cryptosporidium can be released. A person gets infected when the infected stool contaminates a water source or is contacted and then later swallowed. This can happen through drinking or swimming in infected water, swallowing or putting something infected in the mouth (such as fingers), being exposed to human feces through sexual contact (rimming), or by eating uncooked food (such as salad greens) that has been contaminated.

Due to a protective outer shell, Cryptosporidium can live outside of the body for several months and are very resistant to the chlorine-based disinfectants that are often used to treat water sources. This has caused outbreaks in the United States and around the world. Examples of large outbreaks include in 1993, when over 400,000 people were infected by a cryptosporidiosis outbreak in Milwaukee, Wisconsin, and in 2008, when over 200,000 people were infected by an outbreak in the Northampton area of England.


Edward Tyzzer first recognized Cryptosporidium in 1907 when working with mice. This discovery, however, did not lead to the recognition of the cryptosporidiosis as a disease because for over fifty years the organisms were considered rare and benign. In 1955, cryptosporidiosis was discovered in waterfowl with fatal inflammation of the intestine. At this time, Cryptosporidium became considered a disease-causing parasite. The first recognized case of human cryptosporidiosis occurred in 1976, when a young girl from Tennessee suffered from severe gastric problems for two weeks. Since that time, cryptosporidiosis has been found in most species of animals. It has become a better understood health threat and is one of the most common causes of waterborne diseases in industrialized nations.

Risk factors

Cryptosporidiosis is prevalent in every region of the United States and throughout the world. Animal handlers, young children, men who have sex with men, and people who work with those already infected are at the highest risk of becoming infected. Outbreaks are not uncommon and typically occur through contaminated public water supplies, including contaminated drinking water and contaminated swimming pools and lakes. The United States Centers for Disease Control and Prevention estimates that as many as 748,000 people develop cryptosporidiosis in the United States each year, but that many of these cases go unreported.

Cryptosporidiosis transmission.

Cryptosporidiosis transmission.

Causes and symptoms

Cryptosporidiosis is caused by the parasite Cryptosporidium. Symptoms usually begin two to ten days after infection (average of seven days). The most common symptom of cryptosporidiosis is watery diarrhea; however, other symptoms may include dehydration, fever, nausea, stomach cramps or pain, and weight loss. Symptoms usually last one to two weeks, but can go on as long as a few weeks. These symptoms may be continuous or come and go over the time a person is sick. In some cases, a person may have cryptosporidiosis with no symptoms at all.


The diagnosis of cryptosporidiosis usually is done through examining stool samples. Samples may be collected over several days due to the difficulty of detecting Cryptosporidium. The stool samples are most often examined under a microscope. Molecular methods of diagnosis may be used in special circumstances or for research.


There is no specific treatment for cryptosporidiosis, but in some cases, antibiotics may be used. Drugs include nitazoxanide, atovaquone, and paromomycin. Nevertheless, the focus is on treatment of symptoms. Diarrhea may be reduced by taking anti-diarrheal medicine. Dehydration is managed through drinking plenty of fluids. Fluid replacement therapy may be needed for infants or people who suffer from severe dehydration. For many people, no treatment is needed, and cryptosporidiosis will resolve on its own within two weeks of the appearance of symptoms.


For the average healthy person, cryptosporidiosis should clear up without any complications and without any type of treatment. The infection typically lasts under two weeks but may last as long as a month in healthy individuals. Malabsorption (not absorbing enough nutrients from the intestinal tract), wasting syndrome (loss of body mass), hepatitis, cholangitis (inflammation of the bile duct), cholecystitis (inflammation of the gallbladder), and pancreatitis are complications that may be experienced by people diagnosed with cryptosporidiosis, especially those who are immunocompromised. For the most part, cryptosporidiosis does not cause any long-term damage; however, it can turn fatal, especially in elderly and immunocompromised patients if diarrhea and dehydration are not properly managed. People who have immunocompromised systems, for example, those who are receiving cancer chemotherapy, kidney dialysis, have Crohn's disease, or HIV/AIDS, are the most likely to experience serious complications that may be fatal. These people should work with a physician to manage their symptoms.

Harmless, not disease causing. Most often, benign is used to mean not malignant or noncancerous.
Crohn's disease—
A chronic inflammatory intestinal disease that can affect any part of the digestive tract but is most common in the lower part of the small intestine. Crohn's disease is genetic and often requires medical and surgical treatment.
Excessive water loss by the body.
Having a damaged immune system.
An organism that lives in or with another organism, called the host, in parasitism, a type of association characterized by the parasite obtaining benefits from the host, such as food, and the host being injured as a result.


Practicing good hygiene is the best preventative measure against developing cryptosporidiosis. Wash hands with soap and water for at least 20 seconds (about the length of time it takes to sing the happy birthday song) after using the toilet, changing diapers, caring for someone with diarrhea, or handling animals or animal waste. Additionally, hands should be washed before eating or preparing food. Special attention should be paid to children when swimming, offering them frequent bathroom breaks so that they do not contaminate the water and washing their bottoms thoroughly after they use the toilet.


Cryptosporidiosis can be especially harmful to people who are immunocompromised. For this reason, anyone who is immunocompromised should avoid handling animal feces and any close contact with people who have been diagnosed with cryptosporidiosis. A water filter (smaller than one micron) may be effective in filtering out Cryptosporidium eggs. People who suspect their water source may be contaminated should always boil the water they drink or cook and clean with.

See also Parasites ; Zoonoses .



Lamb, Tracey. Immunity to Parasitic Infection. Chichester, UK: John Wiley & Sons, 2012.


Yoder, Jonathan S., et al. “Cryptosporidiosis Surveillance—United States, 2009–2010.” Surveillance Summaries (2012) 61(SS05): 1–12. (accessed October 23, 2012).


Centers for Disease Control and Prevention. “Parasites—Cryptosporidium (also known as ‘Crypto’).” (accessed October 23, 2012).

PubMed Health. “Cryptosporidium Enteritis.” (accessed October 23, 2012).


United States Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA, 30333, (404) 639-3534, (800) CDC-INFO (800-232-4636); TTY: (888) 232-6348,, .

Water Quality Association, 4151 Naperville Road, Lisle, IL, 60532, (630) 505-0160, Fax: (630) 505-9637, .

World Health Organization, Avenue Appia 20, 1211 Geneva 27, Switzerland, +2241 791 21 11, Fax: +2241 791 31 11,, .

Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.