Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
Giardiasis (gee-ar-die-a-sis with a soft "G") is an
infection of the small intestine that is caused by the
parasite, Giardia intestinalis, also
known as Giardia lamblia. It is the most common cause of parasitic
gastrointestinal disease; it is estimated that up
to 2.5 million cases of giardiasis occur each year in the U.S., and up to 20% of the
world's population is chronically infected.
Giardia lamblia exists in two forms, an active form called
a trophozoite, and an inactive form called a cyst. The active trophozoite
attaches to the lining of the small intestine with a "sucker" and is responsible
for causing the signs and symptoms of giardiasis. The trophozoite cannot live
long outside of the body, therefore it cannot spread the infection to others.
The inactive cyst, on the other hand, can exist for prolonged periods outside
the body. When it is ingested, stomach acid activates the cyst, and the cyst
develops into the disease-causing trophozoite. It takes ingestion of only ten
cysts to cause infection. Trophozoites are important not only because they cause
the symptoms of giardiasis, but also because they produce the cysts that exit the body in
the feces and spread the infection to others.
Cysts of Giardia are present in the feces of infected
persons. Thus, the infection is spread from person to person by
contamination of food with feces, or by direct fecal-oral contamination. Cysts
also survive in water, for
example in fresh water lakes and streams. As a result, giardiasis is the most
common cause of water-borne, parasitic illness in the U.S.. Domestic mammals
(for example, dogs, cats, calves) and wild mammals (for example, beavers) can become infected
with Giardia; however, it is not clear how often domestic or wild mammals
transmit giardiasis to humans. Giardiasis also has occurred as outbreaks from
recreational water sources such as swimming pools, water parks, and hot tubs,
most likely because of an infected user rather than a source of water that was
contaminated.
The most common manifestations of giardiasis are diarrhea
and abdominal pain,
particularly cramping; however, diarrhea is not invariable and occurs in 60% to
90% of patients. Other common manifestations include:
bloating,
nausea with or
without vomiting,
malaise, and
fatigue.
Fever is unusual. The severity of
the symptoms may vary greatly from mild or no symptoms to severe symptoms.
Stools may be foul smelling when the Giardia interferes with the absorption of
fat from
the intestine (malabsorption). The illness or the malabsorption may cause loss
of weight.
Symptoms and signs of giardiasis do not begin for at least seven days
following infection, but can occur as long as three or more weeks later. In most
patients the illness is self-limiting and lasts 2-4 weeks. In many patients who
are not treated, however, infection can last for several months to years with
continuing symptoms.
Abdominal pain is pain in the belly and can be acute or chronic. Causes include inflammation, distention of an organ, and loss of the blood supply to an
Nausea is an uneasiness of the stomach that often precedes vomiting. Nausea and vomiting are not diseases, but they are symptoms of many conditions. The
Travelers' diarrhea is generally contracted by eating contaminated food or drinking contaminated water. Food is the primary source of travelers' diarrhea.
Travelers should prepare for their trip by visiting their physician to get the proper vaccinations and obtain the necessary medication if they have a medical
