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Cryptosporidiosis refers to infection by the sporeforming protozoan known as Cryptosporidia. Protozoa are a group of parasites that infect the human intestine, and include the better known Giardia. Cryptosporidia was first identified in 1976 as a cause of disease in humans.


Cryptosporidia are normally passed in the feces of infected persons and animals in the form of cysts. The cysts can remain in the ground and water for months, and when ingested produce symptoms after maturing in the intestine and the bile ducts. When viewed under the microscope, they appear as small bluish-staining round bodies. Most common sources of infection are other humans, water supplies, or reservoirs. These are contaminated by animals that defecate in these areas. An outbreak in Milwaukee in 1993 in which over 400,000 persons were affected was traced to the city's water supply. Cysts of Cryptosporidia are extremely resistant to the disinfectants that are commonly used in most water treatment plants and are incompletely removed by filtration.

Most persons who experience significant symptoms have an altered immune system, and suffer from diseases such as AIDS and cancer. However, as shown in the Milwaukee outbreak, even those with normal immunity can experience symptoms.

Causes and symptoms

Cysts of Cryptosporidia mature in the intestine and bile ducts within three to five days of ingestion. As noted, large-scale infections from contaminated water supplies has been documented. However, human to human transmission (such as occurs in day care centers or through sexual behavior) is also an important cause.

Many individuals can be infected without any illness, but the major symptom is diarrhea, which is often watery and incapacitating. Dehydration, low-grade fever, nausea, and abdominal cramps are frequent.

In those with a normal immune system, the disease usually lasts about 10 days. For patients with altered immunity (immunocompromised), the story is quite different, with diarrhea becoming chronic, debilitating, and even fatal.


Dehydration and malnutrition are the most common effects of infection. In about 20% of AIDS patients, bile duct infection also occurs and causes symptoms similar to gallbladder attacks. Eighty percent or more of those with infection of the bile ducts die from the disease. The lungs and pancreas are also sometimes involved. Cryptosporidia are just one cause of the diarrhea wasting syndrome in AIDS, which results in severe weight loss and malnutrition.


This is based on either finding the characteristic cysts in stool specimens, or on biopsy of an infected organ, such as the intestine.


The first aim of treatment is to avoid dehydration. Oral Rehydration Solution (ORS) or intravenous fluids may be needed. Medications used to treat diarrhea by decreasing intestinal motility (Anti-Motility Agents), such as loperamide or diphenoxylate, are also useful, but should only be used with the advice of a physician.

Treatment aimed directly at Cryptosporidia is only partially effective, and rarely eliminates the organism. The medication most commonly used is paromomycin (Humatin), but others are presently under evaluation.


Cryptosporidia rarely cause a serious disease in persons with normal immune systems. Replacement of fluids is all that is usually needed. On the other hand, those with altered immune systems often suffer for months to years. Paramomycin and other drugs have been able to improve symptoms in over half of those treated. Unfortunately, many organisms are resistant, and recurrence is frequent.


The best way to prevent cryptosporidiosis is to minimize exposure to cysts from infected humans and animals. Proper hand washing technique, especially in day care centers, is recommended.



Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311.


"Cryptosporidiosis." Centers for Disease Control.

Vakil, Nimish B., et al. "Biliary Cryptosporidiosis in HIV-Infected People after the Waterborne Outbreak of Cryptosporidiosis in Milwaukee." New England Journal of Medicine Online.


Anti-motility medications Medications such as loperamide (sold as Imodium), dephenoxylate (sold as Lomotil), or medications containing codeine or narcotics that decrease the ability of the intestine to contract. This can worsen the condition of a patient with dysentery or colitis.

Cyst A protective sac that includes either fluid or the cell of an organism. The cyst enables many organisms to survive in the environment for long periods of time without need for food or water.

Immunocompromised A change or alteration of the immune system that normally serves to fight off infections and other illnesses. This can involve changes in antibodies that the body produces (hygogammaglobulinemia), or defect in the cells that partake in the immune response. Diseases such as AIDS and cancer exhibit changes in the body's natural immunity.

Oral Rehydration Solution (ORS) A liquid preparation developed by the World Health Organization that can decrease fluid loss in persons with diarrhea. Originally developed to be prepared with materials available in the home, commercial preparations have recently come into use.

Parasite An organism that lives on or in another and takes nourishment (food and fluids) from that organism.

Protozoa Group of extremely small single cell (unicellular) or acellular organisms that are found in moist soil or water. They tend to exist as parasites, living off other life forms.

Spore A resistant form of certain species of bacteria, protozoa, and other organisms.

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Cryptosporidium is a genus of protozoan parasites that are infectious to humans and animals. The first reports of human infection with Cryptosporidium were made in 1976; the infection occurs worldwide. Cryptosporidiosis, the enteric disease caused by Cryptosporidium is considered one of the most common parasitic infections in the United States. The largest water-borne outbreak occurred in Milwaukee, Wisconsin, in 1993, when more than 400,000 people were affected. People at highest risk are children less than two years of age, animal handlers, international travelers, homosexual individuals, health care and day-care workers, and the elderly. Cryptosporidiosis infections have been associated with drinking water, recreational water, contaminated food (mainly fruits and vegetables), and direct fecal local contamination.

There are many species of Cryptosporidium, and they infect a wide range of animals. Cryptosporidium parvum is the most common species infecting humans; however, rare cases of C. felis, C. canis, and C. meleagridis infections have been reported in persons with compromised immune systems. There are two main strains of C. parvum, one apparently restricted to humans (anthroponotic), the other infecting animals and humans (zoonotic). C. parvum can also infect humans, cattle, and other domestic animals.

Identification of Cryptosporidium is of both medical and veterinary importance. Cryptosporidium oocysts, the infectious stage of the parasite passed in the feces, predominantly colonize the epithelial cells of the small intestineyet infections have also been found in epithelial cells of both the gastrointestinal and respiratory tract, including the bile ducts, gall bladder, pancreas, stomach, trachea, lungs, and possibly conjunctiva. Asymptomatic infections are common, though the most frequent symptom in humans is diarrhea. Symptoms often wax and wane, but generally remit in fewer than thirty days (with an average of one to two weeks) in most healthy, immunocompetent persons. Symptoms include profuse or watery diarrhea, dehydration, fever, anorexia, nausea, vomiting, stomach cramping, and flatulence. Immunocompromised persons often cannot clear the infection, which significantly contributes to such persons' illness and death.

Transmission routes are fecal-oral, person-to-person, animal-to-person, waterborne, and food-borne. Oocysts of C. parvum are round and 4 to 6 microns in diameter. They are so small that over 10,000 of them would fit on the period at the end of this sentence. The oocysts are highly resistant to chlorine, and to environmental conditions such as frost and heat.

In the laboratory, the most commonly used technique to detect Cryptosporidium oocysts in feces are staining procedures and commercial testing kits. Molecular methods of detection are mainly used as a research tool. Commercial blood tests are not yet available.

Various ways of preventing Cryptosporidium infection include educating the public in personal hygiene, using care in handling animal or human excreta, washing all vegetables and fruits, and avoiding drinking untreated water from lakes, rivers, springs, ponds, or streams. Ways of eliminating oocysts from drinking water are by boiling for one minute or by filter sterilization with either absolute 1.0 micron filters, reverse osmosis filters, or filters that meet NSF (National Sanitation Foundation) standards. Infected food handlers should be removed from work areas, and infected children should be excluded from day-care and recreational water facilities until the infection clears.

There is no established therapy for human cryptosporidiosis. Supportive measures to alleviate symptoms include antidiarrheal medication and management of fluid and electrolyte balance.

Eva M. Kovacs-Nace


American Public Health Association (2000). "Control of Communicable Diseases Manual." 17:134137.

Centers for Disease Control and Prevention (2000). Parasitic PathwaysDrinking Water. Available at

MacKenzie, W. R.; Hoxie, N. J.; Proctor, M. E.; Gradus, M. S.; Blair, K. A.; Peterson, D. E.; Kazmierczak, J. J.; Addiss, D. G.; Fox, K. R.; Rose, J. B.; and Davis, J. P. (1994). "A Massive Outbreak in Milwaukee of Cryptosporidium Infection Transmitted Through the Public Water Supply." New England Journal of Medicine 331:161167.

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Cryptosporidiosis (also referred to as Crypto) is a gastrointestinal illness that results from exposure to the organism Cryptosporidium parvum (C. parvum ). Cryptosporidiosis rose to public attention in the United States in 1993 when more than 100 people died and more than 400,000 people were sickened by Crypto in Milwaukee, Wisconsin.

Cryptosporidiosis is primarily a waterborne illness. People get infected from drinking inadequately treated drinking water, or from swallowing or drinking untreated water from a lake, stream, or swallowing water from a recreational swimming pool. People can become infected with Crypto through contact with the contaminated fecal matter of humans or animals carrying the organism, usually by swallowing food or liquid that has had contact with the contaminated fecal matter. Children at day care centers, day care workers, and health care workers interacting with infected individuals must be vigilant about sanitation to reduce the spread of the organism. Unwashed fruits and vegetables that have been in contact with Cryptoinfected soil have also exposed people to the organism. Cattle and calves contribute significant amounts of Crypto to soils and adjacent water bodies; and wild animals such as elk, deer, bear, and beaver can also carry and spread the organism.

Crypto's symptoms in humans are not unique. They include upset stomach, diarrhea, cramps, weight loss, dehydration, and sometimes fever. Some people do not experience any symptoms. The effects of cryptosporidiosis can be fatal for immunocompromised individuals, including AIDS and cancer patients. Cryptosporidiosis can only be diagnosed by testing a person's stool for the parasite. There is currently no treatment for the illness, which can last several days to a few weeks in healthy individuals.

The organism, C. parvum, is miniscule. It is 3 to 5 microns in size, while the diameter of a human hair is 50 to 200 microns. Giardia lamblia, another significant waterborne parasite, is 5 to 7 microns in size.

Drinking water regulations that went into effect in 1990 focused on the removal and inactivation of Giardia. The threat of Giardia is removed by common water treatment practices, including filtration and disinfection with chlorine. These treatment practices are not as effective against Crypto, which is half the size of Giardia and resistant to disinfection with chlorine. Because drinking water containing Cryptosporidium is difficult to treat, it is important to protect the source of the water against animal waste runoff and other sources of Crypto contamination. Water treatment regulations in effect in 2002 require water utilities to improve treatment plant performance and consistency against Cryptosporidium. The revised drinking water regulations only address exposure from public drinking water sources; they do not address recreational waterborne exposure, or other routes of exposure that tend to be more common.

see also Health, Human; Risk; Water Pollution; Water Treatment.


American Water Works Association. (1990). Water Quality and Treatment: A Handbook of Community Water Supplies, 4th edition. San Francisco: McGraw-Hill.

American Water Works Association and the Society of Civil Engineers. (1998). Water Treatment Plant Design, 3rd edition. San Francisco: McGraw-Hill.

Internet Resource

U.S. Environmental Protection Agency, Office of Water. Available from

Julie Hutchins Cairn

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cryptosporidiosis (krip-toh-sper-id-i-oh-sis) n. an intestinal infection of mammals and birds caused by parasitic protozoa of the genus Cryptosporidium, which is usually transmitted to humans via farm animals. Ingestion of water or milk contaminated with infective oocysts results in severe diarrhoea and abdominal cramps, caused by release of a toxin. Most patients recover in 7–14 days, but the disease can persist in the immunocompromised (including AIDS patients), the elderly, and young children.

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