Giardia lamblia is a topic covered in the Johns Hopkins Antibiotic (ABX) Guide.

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  • Giardia lamblia (syn. G. duodenalis or G. intestinalis)
    • Flagellated bi-nucleated protozoan (see figure)
    • Most common intestinal parasite in North America. [6]
  • Life cycle forms are: 1) highly infectious cysts; and 2) disease-causing trophozoites.
    • Following excystation, trophozoites multiply and colonize the upper small intestine.
    • Trophozoites with flat ventral surface adhere to brush border of enterocytes and cause malabsorption. [5]
  • Transmitted by contaminated water, food, person-to-person, and fecal-oral contact. [4]
    • Surface water is easily contaminated by cysts shed from mammalian hosts such as beaver, sheep, cattle, dogs, or cats.
    • Highly contagious, low infective dose of 10 cysts.
  • Occurs worldwide, specifically in settings of day care centers, over-crowded areas with poor sanitation, and outdoor recreation or swimming pools.

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Last updated: July 2, 2016