Giardiasis
What is Giardiasis?
Giardiasis is a major diarrheal disease found
throughout the world.
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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.
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Causes:
Giardiasis is caused by the flagellate protozoan
Giardia intestinalis (formerly known as G lamblia).
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Pathophysiology:
Infection with Giardia intestinalis most often
results from fecal-oral transmission or ingestion
of contaminated water.
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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
presence of neutral pH and secondary bile
salts.
Cysts are passed into the environment, and the
cycle is repeated.
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Person to person transmission. Person-toperson transmission, often associated with
poor hygiene and sanitation, is a primary
means of infection; diaper changing and
inadequate hand washing are risk factors for
transmission from infected children; children
attending day care centers, as well as daycare workers, have a higher risk of infection
secondary to fecal-oral transmission.
Water-borne transmission. Water-borne
transmission is responsible for a significant
number of epidemics in the United States,
generally following ingestion of unfiltered
surface water; Giardia cysts retain viability in
cold water for as long as 2-3 months.
Venereal transmission. Venereal transmission
occurs through fecal-oral contamination;
food-borne epidemics have been reported,
most commonly secondary to contamination
by infected food-handlers.
Clinical Manifestations:
Clinical signs and symptoms of giardiasis include
the following:
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Diarrhea. Diarrhea is the most common
symptom of acute Giardia infection, occurring
in 90% of symptomatic subjects; marked or
moderate partial villous atrophy in the
duodenum and jejunum can be observed in
histologic sections from asymptomatic
individuals who are infected; in addition to
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disrupting the mucosal epithelium, effects in
the intestinal lumen may contribute to
malabsorption and the production of diarrhea.
Malaise, weakness. Malaise or weakness
occurs due to loss of electrolytes with
diarrhea.
Abdominal distention. Abdominal cramping,
bloating, and flatulence occurs in 70-75% of
symptomatic patients.
Malodorous, greasy stools. Stools become
malodorous, mushy, and greasy.
Anorexia and weight loss. Anorexia, fatigue,
malaise, and weight loss are common; weight
loss occurs in more than 50% of patients and
averages 10 pounds.
Assessment and Diagnostic Findings:
The traditional basis of diagnosis is the
identification of Giardia intestinalis trophozoites or
cysts in the stool of infected patients via a stool ova
and parasite (O&P) examination.
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Stool examination. Stool examination for
trophozoites or cysts is the traditional method
for diagnosing giardiasis; at least 3 stools
taken at 2-day intervals should be examined
for ova and parasites; trophozoites may be
found in fresh, watery stools but disintegrate
rapidly.
Stool antigen detection. Several tests to detect
Giardia antigen in the stool are commercially
available;
these
utilize
either
an
immunofluorescent antibody (IFA) assay or a
capture enzyme-linked immunosorbent assay
(ELISA) against cyst or trophozoite antigens;
these tests have a sensitivity of 85-98% and a
specificity of 90-100%.
String test. The string test (Entero-test)
consists of a gelatin capsule containing a nylon
string with a weight attached to it; the patient
tapes one end of the string to his or her cheek
and swallows the capsule; after the gelatin
dissolves in the stomach, the weight carries
the string into the duodenum; the mucus from
the string is examined for trophozoites in an
iodine or saline wet mount or after fixation and
staining.
Medical Management:
Standard treatment for giardiasis consists of
antibiotic therapy.
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Fluid therapy. Appropriate fluid and electrolyte
management is critical, particularly in patients
with large-volume diarrheal losses.
Diet. No special diet is required; a significant
portion of patients have symptoms of lactose
intolerance (cramping, bloating, diarrhea), and
maintenance on a lactose-free diet for several
months may be helpful.
Activity. Activity restrictions are not indicated;
however, infected subjects who are at risk of
spreading the infection should be isolated and
treated
Pharmacologic Management:
Antibiotic therapy is standard in the treatment of
giardiasis.
Antibiotics. The 2 major classes of drugs that have
proven benefit in the treatment of giardiasis are
nitroimidazole derivatives and acridine dyes;
although most experts recommend metronidazole
and tinidazole as the drugs of choice because the
brief treatment periods encourage good patient
adherence, treatment failures occur in as many as
20% of cases, probably because of resistance;
therefore, treatment with a second-line drug (eg,
mepacrine) may be necessary.
Nursing Management:
Nursing Assessment:
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History. The nature of the overall clinical
manifestations in affected patients is
influenced by numerous factors, including the
parasite load, virulence of the isolate, and the
host immune response.
Physical exam. Physical examination does not
contribute to the diagnosis of giardiasis;
weight loss may be evident, but no known
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unique physical findings are attributable to
giardiasis.
Nursing Diagnosis:
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Diarrhea related to enteric infections.
Fluid volume deficit related to GI losses.
Impaired sense of comfort: pain related to
smooth muscle spasm.
Hyperthermia related to decrease in
circulation secondary to dehydration.
Nursing Interventions:
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Restore Fluid & Electrolyte balance. Weigh
patient daily and note decreased weight;
record number and consistency of stools per
day; if desired, use a fecal incontinence
collector for accurate measurement of output;
monitor and record intake and output; note
oliguria and dark, concentrated urine; discuss
the importance of fluid replacement during
diarrheal episodes.
Reduce pain or discomfort. Assess the extent
and characteristics of pain; give a warm
compress on the abdomen; teach the client and
caregivers about methods to distract from the
pain and set a position that can reduce the
pain.
Improve hyperthermia. Provide tepid sponge
baths; administer antipyretics as prescribed.
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