Infectious colitis

Cryptosporidium parvum

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Last staff update: 23 November 2020

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PubMed Search: Cryptosporidium parvum colitis

Elliot Weisenberg, M.D.
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Cite this page: Weisenberg E. Cryptosporidium parvum. website. Accessed June 2nd, 2023.
Definition / general
  • Disease caused by infection with Cryptosporidium species, a protozoal parasite
  • Traditionally considered a coccidian parasite, but recent evidence suggests it may be a gregarine parasite
  • Cryptosporidium has a worldwide distribution (excepting Antarctica)
  • Infection is usually person to person through the fecal-oral route, via ingestion of infective oocysts
  • In some cases, zoonotic infection from sheep, cows, pigs, rodents, companion animals and other animals may occur
  • The oocysts are hardy and are not killed by chlorination of drinking water
  • Developing world: primarily affects children under age 5, and in most cases persistent diarrhea occurs that may be compounded by malnutrition; uncommon in adults
  • Developed world:
    • More common in children but not to the extent of the developing world
    • Disease due to:
      • Spread of pediatric cases in day care centers
      • Travel to developed countries
      • Spread in mental institutions
      • Contaminated recreational water, including swimming pools, rivers, lakes, fountains
        • Cryptosporidium is the most common cause of waterborne disease in recreational water
      • Animal handlers
      • Food borne spread
      • Breakdowns in municipal water purification systems
    • United States: 300,000 to 750,000 cases each year, more commonly in summer
    • The largest known outbreak occurred in Milwaukee, Wisconsin in 1993, affecting an estimated 400,000 people, although this type of spread is now uncommon in the developed world
    • Sexual transmission in men who have sex with men has been reported
    • Disease is common in immunosuppressed patients especially AIDS patients with CD4 counts under 100

  • There are over 20 species of cryptosporidium:
    • C. hominis, the human genotype that primarily infects people and C. parvum, the bovine genotype, are the most important causes of human disease
    • C. hominis was formerly known as C. parvum anthroponotic genotype 1
    • C. meleagridis, C. Canis, C. felis, C. ubiquitum, C. cuniculus, C. suis, C. muris, and other species are known to cause human disease
  • Infection is most common in terminal ileum and proximal colon
  • Disease also occurs in proximal small intestine, distal colon, gallbladder, bile ducts and pancreas
  • Widespread disease generally occurs with severe immunosuppression, and may involve respiratory tract
  • Ingested oocysts excyst in stomach and small intestine, releasing 4 infective sporozoites that bind to intestinal epithelial cells
  • The sporozoite becomes embedded in cell membrane in a parasitophorous vacuole
  • Inside the vacuole, the sporozoite undergoes merogony (asexual reproduction) to become trophozoites
  • The trophozoites divide to become type I meronts that mature, causing the parasitophorous vacuole to rupture, releasing motile merozoites that bind to epithelial cells and are engulfed
  • Merogony is repeated or sexual differentiation occurs and merozoites differentiate into micro and macrogamonts
  • The microgamonts release microgametes that penetrate cell walls of cells infected with macrogamonts
  • The macrogamont and microgametes fuse and form zygotes
  • The zygote undergoes meiosis to form an oocyst containing 4 sporozoites
  • There are thin walled and thick walled forms of oocysts
  • The thin walled form excysts in the host causing autoinfection while the thick walled oocyst is shed in the environment
  • Infection causes enterocolitis or malabsorption
Clinical features
  • The incubation period is usually about one week but may be from 1 to 30 days
  • In immunocompetent individuals, acute but self-limited profuse watery diarrhea usually occurs
  • In children in the developing world, persistent diarrhea occurs but most patients recover
  • In immunosuppressed patients, chronic diarrhea occurs that is often debilitating
  • In immunosuppressed patients, acalculous cholecystitis, sclerosing cholangitis, pancreatitis, biliary strictures and respiratory disease may occur
  • The diagnosis is usually made by visualization of cysts in stool using immunofluorescence or a modified acid fast stain
  • It is important to communicate with the laboratory if there is a suspicion of cryptosporidiosis, as not all laboratories routinely test stool for Cryptosporidiium
  • On occasion, the diagnosis is made on biopsy (see microscopic description)
Prognostic factors
  • In immunocompetent adults, self limited diarrhea lasting one or two days is the rule
  • If the CD4 count is under 100, chronic diarrhea occurs
  • In HIV+ patients with CD4 counts under 50 and other immunosuppressed patients with markedly suppressed T cell function, fulminant diarrhea occurs
  • In HIV+ patients with CD4 counts greater than 150 - 180, self-limited diarrhea usually occurs
  • The ultimate prognosis in chronic and fulminant diarrhea in HIV+ patients is related to the success of therapy to reconstitute the immune system
  • In the developing world, children under 5 usually suffer from persistent diarrhea that is often complicated by malnutrition
Case reports
  • Nitazoxanide reduces the severity of disease in immunocompetent patients and has been approved by the FDA for these patients; its effectiveness in immunocompromised patients is unclear although it is used in that setting
  • Reconstitution of the immune system through highly active anti-viral therapy in AIDS patients or reduction in immunosuppression in other settings is important
Microscopic (histologic) description
  • In tissue biopsies, 2 - 5 μm basophilic round bodies are seen protruding from the apex of enterocytes ("blue beads") within the cell membrane; highlight with Giemsa stain
  • Villous atrophy, crypt hyperplasia, cryptitis and increased mixed inflammatory cells within the lamina propria may be seen
Microscopic (histologic) images

Images hosted on other servers:
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Small blue organisms at luminal border

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Modified acid-fast oocyst in stool

Positive stains
  • Modified AFB, immunofluorescence
Differential diagnosis
  • Cyclospora: oocysts are 8 μm, not 2-5 microns
  • Isospora: oocysts are 20 - 30 μm
  • Microsporidium: an intracellular fungus that is not modified acid fast but may coinfect with Cryptosporidium
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