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- Intestinal infection caused by the protozoan parasite Giardia lamblia:
- G. lamblia is also called Giardia duodenalis and Giardia intestinalis.
- Infection results from ingestion of cysts, which transform into trophozoites and colonize the small intestine to cause symptoms.
- The infectious cycle is continued when trophozoites encyst in the small intestine to be subsequently transmitted through water, food, or hands contaminated by feces of an infected person.
- Most infections result from fecal–oral transmission or ingestion of contaminated water (e.g., swimming).
- Less commonly acquired through contaminated food
- Predominant age:
- All ages but most common in early childhood (ages 1 to 9 years) and adults 35 to 44 years
- Predominant gender:
- Male > female (slightly)
- Minimal seasonal variability; slight increase in summer and early fall
- Most common in early childhood
- Chronic infection in children can lead to intestinal malabsorption (may also be associated with growth restriction).
- 10% of cases of traveler’s diarrhea are caused by parasites, most commonly Giardia (1).
- >19,000 cases per year from U.S. states where Giardia is reportable:
- Giardia is currently not reportable in Indiana, Kentucky, Mississippi, North Carolina, and Texas.
Etiology and Pathophysiology
Giardia trophozoites colonize the surface of the proximal small intestine: The mechanism of diarrhea is unknown.
No known genetic risk factors
- Daycare centers
- Anal intercourse
- Wilderness camping
- Travel to developing countries
- Children adopted from developing countries
- Public swimming pools
- Pets with Giardia infection/diarrhea
- Hand hygiene
- Water purification when camping and when traveling to developing countries
- Properly cook all foods.
Commonly Associated Conditions
Hypogammaglobulinemia, IgA deficiency, and immunosuppression are associated with prolonged course of the disease and treatment failures.