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  • Acute diarrhea, especially in children in developing countries.

  • Outbreaks of diarrhea secondary to contaminated water or food.

  • Prolonged diarrhea in immunocompromised persons.

  • Diagnosis mostly by identifying organisms in specially stained stool specimens.


The causes of coccidiosis are Cryptosporidium species (C parvum, C hominis, and others); Cystoisospora (formerly Isospora) belli; Cyclospora cayetanensis; and Sarcocystis species. Microsporidiosis is caused by at least 14 species, most commonly Enterocytozoon bieneusi and Encephalitozoon intestinalis. These infections occur worldwide, particularly in the tropics and in regions where hygiene is poor. They are causes of endemic childhood gastroenteritis (particularly in malnourished children in developing countries); institutional and community outbreaks of diarrhea; traveler’s diarrhea; and acute and chronic diarrhea in immunosuppressed patients, in particular those with AIDS. They are all notable for the potential to cause prolonged diarrhea, often lasting for a number of weeks. Clustering occurs in households, day care centers, and among sexual partners.

The infectious agents are oocysts (coccidiosis) or spores (microsporidiosis) transmitted from person to person or by contaminated drinking or swimming water or food. Ingested oocysts release sporozoites that invade and multiply in enterocytes, primarily in the small bowel. Coccidian oocysts and microsporidian cysts can remain viable in the environment for years.

Cryptosporidiosis is a zoonosis (C parvum principally infects cattle), but most human infections are acquired from humans, in particular with C hominus. Cryptosporidia are highly infectious and readily transmitted in day care settings and households. They have caused large community outbreaks due to contaminated water supplies (causing about 400,000 illnesses in Milwaukee in 1993 and about 2780 illnesses in Oregon in 2013) and are the leading cause of recreational water–associated outbreaks of gastroenteritis. In the developing world, cryptosporidiosis is a leading cause of childhood diarrhea. In a study of causes of moderate-to-severe diarrhea in Asia and Africa, Cryptosporidium was the second most commonly identified pathogen in children under 2 years of age.

C belli and C cayetanensis appear to infect only humans. C cayetanensis has caused a number of food-borne outbreaks in the United States in recent years, most commonly associated with imported fresh produce. Sarcocystis infects many species; humans are intermediate hosts (infected by ingestion of fecal sporocysts) for some species but definitive hosts for Sarcocystis bovihominis and Sarcocystis suihominis (infected by ingestion of tissue cysts in undercooked beef and pork, respectively).


A. Symptoms and Signs

1. Coccidiosis


The incubation period appears to be approximately 14 days. In developing countries, disease is primarily in children under 5 years of age, causing 5–10% of childhood diarrhea. Presenting symptoms in children include acute watery diarrhea, abdominal pain, and cramps, with rapid resolution in most patients; however, ...

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