Answer:
Giardiasis is the disease caused by infection of the small intestine by the protozoan Giardia lamblia. Giardiasis is usually asymptomatic, but can cause diarrhea and intestinal malabsorption of fats. Giardiasis is present practically all over the world, but mainly affects children in low-income populations and regions of tropical or subtropical climate or in the very hot sun heat that can cause disease.
Giardiasis is mainly caused by ingestion of water or food contaminated by feces containing at least 10 to 100 Giardia lamblia cysts. Exposure of this protozoan to gastric juice does not cause its elimination, but the alkaline ph of the duodenum causes the cysts to transform by maturing their cystic form into trophozoites, which adhere to the small intestine wall through a structure called "ventral disc" that acts like a suction cup adhering to the intestinal epithelium. About 9 days (6 to 15) after infection, the person begins to eliminate cysts from the stool, which can then contaminate others. Therefore the small intestine is where the giardiasis life cycle occurs.
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