completes the construction of its cyst and is shed into
the outside environment through the person’s feces.Symptoms
About 15% of people who swallow cysts are
asymptomatic. These cases are usually detected only if
the person’s stool is tested during a community out-
break. They are significant, however, because persons
carrying the cysts in their digestive tract, known as
carriers, can still transmit giardiasis to others even if
they do not develop the symptoms of the illness. It is
estimated that between 30 and 60% of children in day-
care centers and adults on Native American reserva-
tions are carriers ofG. lamblia. Some domestic and wild
animals can also be carriers ofG. lamblia,dogsand
beavers being the most common animal reservoirs.
Of the patients who have symptoms, 90% develop
acute diarrhea within 7 to 10 days of ingesting the
cysts; and 70–75% have abdominal cramps, bloating,
vomiting, and flatulence (the passage of intestinal
gas). A small percentage of patients develop symptoms
within 3 days of swallowing the cysts, including violent
diarrhea, extremely foul-smelling intestinal gas, severe
vomiting, fever, and headache. Most patients lose
their appetite, and 50% lose weight—an average of
10 pounds in adults. Without treatment, these symp-
toms can last for as long as 7 weeks or even longer.
Between 20 and 40% of adults with giardiasis
develop a temporary difficulty with digesting lactose,
a sugar found in milk or milk products. This condition
is called lactose intolerance and may last for a month
or so after treatment with anti-parasite medications
for giardiasis. Having lactose intolerance does not
mean that the person has become reinfected.
There is no universal pattern to recovery from
giardiasis. It is rarely fatal except in severely dehy-
drated and malnourished children, but may develop
into chronic forms—malabsorption syndrome in
adults and failure to thrive in children. Chronic giar-
diasis in adults is characterized by episodes of diarrhea
that come and go, alternating with periods ofconsti-
pationand normal bowel movements. Other symp-
toms of chronic giardiasis in adults include:
Ongoing weight loss apart from intentional weight
reduction.
Steatorrhea. Steatorrhea is the medical term for the
passage of large amounts of fat or greasy-looking
material in the stool.
Discomfort in the stomach or abdomen that is worse
after a meal.
Persistent bad breath or burping that smells like sulfur.Ongoing bloating, flatulence, or abdominal cramping.
Recurrent headaches.
Malaise (general feeling of sickness), fatigue, or
weakness.
The symptoms of chronic giardiasis in children
include:
Failure to grow and gain weight at a normal rate for
the child’s age and sex.
Recurrent episodes of pale, frothy, foul-smelling diarrhea.
Loss of appetite.
Abdominal pain and vomiting.
Nutritional deficiencies caused by the inability to
absorb nutrients in food.Demographics
In the United States and other developed countries,
giardiasis is most likely to affect children, particularly
children in daycare centers. About 20 to 25% of the
children in daycare centers are infected with giardiasis
even though they may not be symptomatic. Most of the
community outbreaks in the United States since the
1980s, in fact, began in daycare centers.
Older adolescents and adults are more likely to be
infected with giardiasis while hiking or traveling
abroad.G. lambliais a common cause of so-called
traveler’s diarrhea, although it is not the only organism
that causes it. Giardiasis acquired its nickname of ‘‘bea-
ver fever’’ because backpackers and hikers who drink
water from or swim in streams close to beaver colonies
are likely to ingestG. lambliacysts shed into the water
by infected animals. The CDC reports that as many as
80% of water samples from lakes, streams, and ponds
in the United States containG. lambliacysts.
Outbreaks of giardiasis are most likely to occur in
Canada and the United States during warmer weather,
particularly in summer and fall. Race does not appear
to be a factor in contracting giardiasis; however, males
in all age groups are about 1.2 times more likely than
females to develop the disease.Risk factors
Some people are at increased risk of contracting
giardiasis because of their location or lifestyle:
Parents of infected small children.
Employees (and their family members) of daycare
centers in which some of the children are not yet
toilet-trained.
Employees (and their family members) of nursing
homes or other custodial facilities.Giardiasis