What is Giardiasis?
Giardiasis is a major diarrheal disease found throughout the world.
The flagellate protozoan Giardia intestinalis (previously known as G.
lamblia or G. duodenalis), its causative agent, is the mo
...
What is Giardiasis?
Giardiasis is a major diarrheal disease found throughout the world.
The flagellate protozoan Giardia intestinalis (previously known as G.
lamblia or G. duodenalis), its causative agent, is the most commonly identified
intestinal parasite in the United States and the most common protozoal intestinal
parasite isolated worldwide.
Giardiasis usually represents a zoonosis with cross-infectivity between animals
and humans.
G. intestinalis can cause asymptomatic colonization or acute or chronic
diarrheal illness.
The organism has been found in as many as 80% of raw water supplies from
lakes, streams, and ponds and in as many as 15% of filtered water samples.
Pathophysiology
Infection with Giardia intestinalis most often results from fecal-oral transmission
or ingestion of contaminated water.
Person-to-person spread is common, with 25% of family members with
infected children themselves becoming infected.
Giardia has one of the simplest life cycles of all human parasites; the life cycle
is composed of 2 stages: (1) the trophozoite, which exists freely in the human
small intestine; and (2) the cyst, which is passed into the environment.
Upon ingestion of the cyst (see the second image below), contained in
contaminated water or food, excystation occurs in the stomach and the
duodenum in the presence of acid and pancreatic enzymes.
The trophozoites pass into the small bowel where they multiply rapidly, with a
doubling time of 9-12 hours; as trophozoites pass into the large bowel,
encystation occurs in the
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