DEFINITION:

A protozoan infectious disease of the small bowel resulting in a secretory diarrhea.

EPIDEMIOLOGY:

• incidence: ? 2nd most common protozoan cause of enteritis (1-9%)
• risk factors:
  • age: all ages
  • season: ?
  • route: direct: sexual (VD)
  • indirect: water, food (salmon)
  • environ: endemic and epidemic
  • The geographic risks include Lenningrad, the Rocky Mountains, and remote lakes (beaver fever). High risk groups include day-care kids, gays, lower SEC, institutionalized people, travellers, campers, immunocomprimised (IgA deficiency, agammablobulin-emia), and those with hypochlorhydria, HLA-A1, -B12, and blood Group A.
• intubation period: 7-21 days

PATHOGENESIS:

• Cysts are ingested in contaminated water or acquired directly (gays). They travel to the distal duodenum and jejunum where they undergo excystation (pH 6.4-7.4) to form trophozoites. Here the trophozoites multiply by binary fission and then attach themselves to the villous surface of the small bowel mucosa causing abdominal distress, cramps, and diarrhea. The cysts and trophozoites are passed in steatorrheic foul stools. The trophozoites disintegrate but the cysts survive in infected water (viable up to 3 months). The pathogenic mechanisms are still unclear but direct mechanical injury to the mucosa is probably the major factor for the diarrhea.
• In human breast milk, there is a lipase and secretory IgA which kill Giardia lamblia and Entamoeba histolytica. While chlorination does not kill giardial cysts, the trophozoites are destroyed by drying and boiling.
• Chronic Malabsorption
  • the only common primary infection causing chronic malabsorption
  • perhaps most common cause of chronic malabsorption in N. America
  • EM studies have revealed the intestinal mucosa to be covered by a thick mucous coat with may interfere with nutrient contact with the brush border -> malabsorption

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MANAGEMENT: