(Giardiasis)
Symptomatic
infection causes a broad spectrum of clinical manifestations.Acute
watery diarrhea with abdominal pain may develop in patients with
clinical illness, or they may experience a protracted, intermittent,
often debilitating disease, which is characterized by passage of
foul-smelling stools associated with flatulence, abdominal
distention, and anorexia. Anorexia combined with malabsorption can
lead to significant weight loss, failure to thrive, and anemia.
Asymptomatic infection is common.
Giardia lamblia is a
flagellate protozoan that exists in trophozoite and cyst forms; the
infective form is the cyst.Infection is limited to the small
intestine and biliary tract.
Giardiasis has a
worldwide distribution. Humans are the principal reservior of
infection, but Giardia organisms can infect dogs, cats, beavers, and
other animals. These animals can contaminate water with feces
containing cysts that are infectious for humans. Persons become
infected directly (by hand-to-mouth transfer of cysts from feces of
an infected person) or indirectly (by ingestion of fecally
contaminated water or food). Many persons who become infected with G
lamblia remain asymptomatic.Most community-wide epidemics result
from a contaminated water suply. Epidemics resulting from porson-to-person
transmission occur in child care centers and in institutions for
mentally retarded persons . Staff and family members in contact with
persons in these settings occasionally become infected. Humoral
immunodeficiencies predispose to chronic symptomatic G lamblia
infections. Surveys conducted in the United States have demonstrated
prevalence rates of Giarbia organisms in stool specimens that range
from 1% to 20%, depending on geographic location and age. Duration
of cyst excretion is variable and may be months. The disease is
communicable for as long as the infected person excretes cysts.
The incubation period usually is 1 to 4 weeks.
|
|
Identification of trophozoites or cysts on
direct smear examination or immunofluorescent antibody(IFA) testing of stool
specimens or duodenal fluid or detection of G lamblia antigens in these
specimens by enzyme immunoassay (EIA) is diagnostic. Commercially available EIA
techniques for stool specimens have greater sensitivity than microscopy but fail
to detect other parasites. One commercially available IFA test allows
microscopic detection of Giardia and Cryptosporidium species in stool with a
sensitivity of approximately 75% . A single direct smear examination of stool
has a sensitivity of 50% to 75% , which is increased to approximately 95% by
testing 3 specimens. To enhance detection, microscopic examination of stool
specimens or duodenal fluid should be performed soon after they are obtained ,
or stool should be mixed, placed in fixative, concentrated, and examined by wet
mount and permanent stain. Commercially available stool collection kits
containing a vial of 10% formalin and a vial of polyvinyl alcohol fixative in
chilproof of containers are convenient for preserving stool specimens collected
at home . Laboratories can reduce reagent and personnel costs by pooling
specimens before evaluation by microscopy or EIA. Examination of duodenal
contents obtained by direct aspiration or by using a commercially available
string test (Entero-Test,HDC Corporation, San Jose , Calif) is a more sensitive
procedure than examination of a single stool specimen. Rarely, duodenal biopsy
is required for diagnosis.
Metronidazole is the drug of choice; a 5- to 7-day
course of therapy has a cure rate of 80% to 95%. Tinidazole, a nitroimidazole ,
has a cure rate of 90% to 100% after a single dose, but limited safety and
efficacy data are available in children. Furazolidone is 72% to 100% effective
when given for 7 to 10 days and has an acceptable flavor for pediatric use .
Albendazole has been shown to be as effective as metronidazole for treating
giardiasis in children, and it has fewer adverse effects. Albendazole can be
formulated into a suspension and has been given to children 2 years of age or
older at a dose of 400 mg by mouth daily for 5 days.paromomycin, a nonabsorbable
aminoglycoside that is 50% to 70% effective, is recommended for treatment of
symptomatic infection in pregnant women. Quinacrine can be obtained by special
order (see Drugs for Parasitic Infections , p 693).
If therapy fails, a course can be repeated with the same drug. Relapse is
common in immunocompromised patients who may require prolonged treatment.
Some experts recommend combination therapy for giardiasis in immunocompromised
patients who are unreponsive to courses of both drugs used separately.
Treatment of asymptomatic carriers generally is not recommended.Possible
exceptions to prevent transmission are in households of patients with hypogamma
globulinemia or cystic fibrosis and in pregnant women with toddlers.
In addition to standard precautions, contact precautions for the duration of
illness are recommended for diapered and incontinent children.
In child care centers, improved sanitation and personal hygiene should be
emphasized (see also Children in Out-of-Home Child Care, p 105). Hand washing by
staff and children should be emphasized, especially after toilet use or handling
of soiled diapers. When an outbreak is suspected, the local health department
should be contacted, and an epidemiologic investigation should be undertaken to
identify and treat all symptomatic children, child care workers, and family
members infected with G lamblia, Persons with diarrhea should be excluded from
the child care center until they become asymptomatic.Treatment of asymptomatic
carriers is not effective for outbreak control. Exclusion of carriers from child
care is not recommended.
 Waterborne outbreaks can be prevented by the
combination of adequate filtration of water from surface water sources (eg,
lakes, rivers, streams), chlorination , and maintenance of water distribution
systems.
Backpackers, campers , and persons likely to be exposed to
contaminated water should avoid drinking directly from streams. Boiling of water
will kill the infective cysts and other waterborne pathogens.
|
