Cryptosporidium parvum is a protozoan parasite can infect mammals, birds, reptiles and even fish.

It belongs to a larger group of parasites that are collectively called “coccidia”. Cryptosporidium is a common cause of human diarrhea, although it’s less common than diarrhea caused by human viruses. Large outbreaks of Cryptosporidiosis have occurred in cities when the city water supply has become contaminated. Cryptosporidiosis is especially common in the young, both in animals and in man. Most infected people recover without treatment but C. parvum can cause especially severe disease in people that have weakened immune systems or who are positive for HIV.


People and animals are infected with C. parvum when they allow fecal material from an infected person or animal to enter their mouth. The organism reproduces rapidly in the intestine, and the feces of infected animals and humans are highly infectious. The disease is diagnosed by finding oocysts in the feces of patient. The oocysts are highly resistant to disinfectants. Infected feces from wild or domestic animals may cause ponds, lakes, and reservoirs to become contaminated.

Two to ten days after ingesting the organism, a watery diarhea may develop, often accompanied by cramping, nausea, and malaise. Healthy individuals generally recover in 3-14 days without any treatment. In people whose immune systems are compromised, the diarrhea can be much worse, and the organism can sometimes invade organs other than the intestine.

There is no effective drug therapy; the treatment is supportive and aimed at preventing dehydration. If you’re infected, you should drink plenty of fluids and get plenty of rest.

Relative Risks

Most human cases have occurred as a result of accidental contamination of urban water supplies. Those who care for infected animals or humans are also at increased risk of being infected. Infection is most likely to be present in young animals with diarrhea - a worker changing diapers at a day care center or a technician caring for a calf with diarrhea would both be at increased risk. Any young animal with diarrhea, be they a mammal, a reptile, or a bird, should be considered potentially infectious. The animal most likely to be infected is a calf less than one year old who has diarrhea.


The single most effective preventive measure that you could take to protect yourself would be thorough, regular handwashing with soap and warm water after handling animals or infants with diarrhea. In day care centers, those changing diapers should wash their hands thoroughly between diaper changes, even if they wear gloves. If you’ve just cared for a calf or a lamb with diarrhea, wash your hands before moving on to the next task. If you are in a situation in which splattering of diarrheic feces is possible (as from the swinging tail of a calf), then consider wearing a surgery mask or face shield to protect your mouth.

Good ways to infect yourself would be to eat or drink in the animal facility, or to fail to wash your hands before eating, drinking or smoking after working with animals.

If you work with young animals with diarrhea, and you develop a severe watery diarrhea, you should report the illness to your supervisor and consult with a physician at Employee Health Services. An accurate diagnosis can be made by a microscopic examination of feces.