What Is Cryptosporidiosis?

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 is 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.

Routes of Infection

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 diarrhea may develop, often accompanied by cramping, nausea, and malaise. Healthy individuals generally recover in three to 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.


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. 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 hand washing with soap and warm water after handling animals with diarrhea. 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 Service (860-679-2893). An accurate diagnosis can be made by a microscopic examination of feces.