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Giardia lamblia

Historical background

Giardia  was  originally  observed  by  von  Leeuwenhoek  in  1681,  in  his  own
diarrheal  stool,  and  was  described  by  Vilem  Dusan  Lambl  in  1859  and  by
Alfred Giard in 1895.
Although  G  intestinalis  is  one  of  the  first  protozoan  parasites  described,  its
role,  as  a  pathogenic  organism  was  not  recognized  until  the  1970s,  after
outbreaks.

Morphology:
The cyst form of the protozoan is smooth-walled and oval in shape, measuring
8-12 µm long by 7-10 µm wide. As the cyst matures, nuclear division occurs.
Mature  cyst  contains  4  nuclei  and  then  the  cyst  releases  2  trophozoites  upon
excystation.  Once  the  host  is  infected,  trophozoites  may  appear  in  the
duodenum within minutes. Excystation occurs within 5 minutes of exposure of
the cysts to an environment with a pH between 1.3 and 2.7.
The  trophozoite  form  of  G  lamblia  is  teardrop-shaped  and  measures  9-21
micrometers  long  by  5-15  micrometers  wide.  The  trophozoite  has  a  convex
dorsal  surface  and  a  flat  ventral  surface  that  contains  the  ventral  disk.  The
trophozoite also contains long axostyles, 4 pairs of flagella, directed posteriorly,
that  aid  the  parasite  in  moving.  Two  symmetric  nuclei  with  prominent
karyosomes  produce  the  characteristic  face  like  image  that  appears  on  stained
preparations.

Life cycle:
  Giardia lamblia (also known as Giardia intestinalis, or Giardia duodenalis)
is  a  microscopic  parasite  that  causes  diarrheal  illness  known  as  giardiasis.
Giardia cyst (the infective stage) is found on surfaces or in soil, food, or water
that  has  been  contaminated  with  feces  from  infected  subjects.  Giardia  cyst  is
protected  by  an  outer  shell  that  allows  it  to  survive  outside  the  body  for  long
periods of time and makes it tolerant to chlorine disinfection. The parasite can
be  spread  in  different  ways;  water  (drinking  water  and  recreational  water)  is
regarded  the  most  common  mode  of  transmission.  Cysts  are  responsible  for
transmission of giardiasis.
(1)  Both  cysts  and  trophozoites  can  be  found  in  the  feces  (both  regarded  as

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diagnostic stages).
(2) The cysts are hardy and can survive several months in cold water. Infection
occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral
route  (hands  or  fomites).  Because  the  cysts  are  infectious  when  passed  in  the
stool or shortly afterward, person-to-person transmission is possible.
(3) In the small intestine, excystation releases trophozoites (each cyst produces
two trophozoites).
(4) Trophozoites multiply by longitudinal binary fission, remaining in the lumen
of the proximal small bowel where they can be free or attached to the mucosa
by a ventral sucking disk
(5) Encystation occurs as the parasites transit toward the colon. The cyst is the
stage found most commonly in non-diarrheal feces.

Geographic Distribution:
Worldwide,  more  prevalent  in  warm  climates,  especially  among  children.
Giardia intestinalis has been isolated from the stools of beavers, dogs, cats, and
primates.  Beavers  may  be  an  important  reservoir  host  for  G.  intestinalis.
However there is a small risk from getting infection from cats and dogs because
of differences among the human and cats or dogs strains 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. Giardia species are endemic
in  areas  of  the  world  that  have  poor  sanitation.  In  developing  countries,  the
disease  is  an  important  cause  of  morbidity.  Water-borne  and  food-borne
outbreaks are common.

Clinical Picture:
The  mechanisms  by  which  Giardia  causes  diarrhea  and  intestinal
malabsorption  are  probably  multifactorial.

The proposed pathological

mechanisms  include  damage  to  the  endothelial  brush  border,  enterotoxins,
immunologic reactions, and altered gut motility and fluid hyper secretion.
G. intestinalis can cause asymptomatic colonization , acute or chronic diarrheal
illness and malabsorption. Because ingestion of as few as 10 Giardia cysts may
be  sufficient  to  cause  infection,  giardiasis  is  common  crowded  areas  and
institutions in developed countries.
High-risk  groups  for  giardiasis  include  travelers  to  highly  endemic  areas,
patients  with  hypochlorhydria,  immune  compromised  individuals,  and  certain
sexually active homosexual men, patients with malnutrition, patients with cystic

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fibrosis  and  blood  group  A  and  crowded  areas.  Cyst  passage  rates  as  high  as
20%  have  been  reported  among  certain  groups  of  sexually  active  homosexual
men. These individuals were frequently symptomatic.
Acute giardiasis develops after an incubation period of 1 to 14 days (average of
7 days) and usually lasts 1 to 3 weeks. Acute symptoms include:
•  Diarrhea
•  Gas
•  Greasy stools that tend to float
•  Stomach or abdominal cramps
•  Upset stomach or nausea/vomiting
•  Dehydration (loss of fluids)
The symptoms of giardiasis might seem to resolve, but come back again after
several  days  or  weeks.  Giardiasis  can  cause  weight  loss  and  failure  to  absorb
fat, lactose, vitamin A and vitamin B12.
In  children,  severe  giardiasis  might  delay  physical  and  mental  growth,  slow
development, and cause malnutrition.

Diagnosis:
Stool examination:
The  traditional  basis  of  diagnosis  is  identification  of  Giardia  intestinalis
trophozoites or cysts in the stool of infected patients via a stool ova and parasite
(O&P,  i.e.  general  stool  examination)  examination.  Fresh  stool  can  be  mixed
with  an  iodine  solution  or  methylene  blue  and  examined  for  cysts  on  a  wet
mount.  If  not  immediately  examined,  stool  should  be  preserved  in  10%
formalin, with subsequent trichrome or iron hematoxylin staining. Trophozoites
may be found in fresh, watery stools but disintegrate rapidly. If the stool is not
fresh  or  is  semi  formed  to  formed,  trophozoites  will  not  be  found.  Cysts  are
passed in soft and formed stools.
Ideally, 3 stool samples from each patient on different days should be examined
because of potential variations in fecal excretion rate of cysts. G intestinalis is
identified  in  50-70%  of  patients  after  a  single  stool  examination  and  in  more
than  90%  after  3  stool  examinations.  Stool  concentration  methods  are  also
beneficial  in  the  diagnosis  of  giardiasis  when  there  is  low  excretion  rate  of
cysts.
Cyst  passage  and  may  lag  behind  the  onset  of  symptoms  by  a  week  or  more.
Because many antibiotics, enemas, laxatives, and barium studies mask or cause
the disappearance of parasites from the stools, microscopic examination should

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be  postponed  for  5-10  days  following  these  interventions.  Fecal  leukocytes
should not be visualized in stool samples of patients with giardiasis.
Duodenal Aspiration:
Aspiration of duodenal contents and demonstration of trophozoites also have
been used for diagnosis but this is more invasive than stool examination and, in
direct  comparison  studies  to  stool  microscopy,  may  have  a  lower  diagnostic
yield.
Stool antigen and serology:
Stool  antigen  enzyme-linked  immunosorbent  assays  also  are  available.  Since
levels  of  immunoglobulin  G  (IgG)  remain  elevated  for  long  periods,  they  are
not beneficial in making the diagnosis of acute giardiasis. Serum anti-Giardia
immunoglobulin  M  (IgM)  can  be  beneficial  in  distinguishing  between  acute
infections and past infections.

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 string is left in place for 4-6 hours or overnight while the patient is fasting.
After  removal,  it  is  examined  for  bilious  staining,  which  indicates  successful
passage  into  the  duodenum.  The  mucus  from  the  string  is  examined  for
trophozoites in an iodine or saline wet mount or after fixation and staining.

Treatment
Standard treatment for giardiasis consists of antibiotic therapy. Metronidazole is
the most commonly prescribed antibiotic for this condition. The recommended
adult  dose  is  250  mg  orally  three  times  daily  (tid)  for  5-7  days.  However,
tinidazole is now approved and considered a first-line agent .The recommended
dose is 50 mg/kg orally once.
Paromomycin  has  been  recommended  for  use  in  pregnancy  because  systemic
absorption is low, but the cure rate is lower than other agents.
Appropriate fluid and electrolyte management is critical, particularly in patients
with large-volume diarrheal losses.

Prevention

• Infected persons and persons at risk should carefully wash their hands

after they have any contact with feces.

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• Infected individuals should be prevented from using swimming pools,

lakes, and rivers until they are symptom-free for few weeks.

• Chlorination, sedimentation, and filtration methods should be

implemented  to  adequately  purify  public  water  supplies.  Effective
chlorine  inactivation  of  Giardia  cysts  in  water  requires  an  optimal
chlorine  concentration,  water  pH,  turbidity,  temperature,  and  contact
time.  These  variables  cannot  be  appropriately  controlled  in  all  water
supply  units,  and  they  are  particularly  difficult  to  control  in  swimming
pools.

• Drinking water can be purified by using filtration (pore size, < 1 µm) or

by briskly boiling water for at least 5 minutes. Chlorine or iodine water
treatments are less effective than boiling or filtration, but they may be
used as alternatives when other methods are not available

• Advise travelers to endemic areas to avoid eating uncooked foods that

may have been grown, washed, or prepared with contaminated water.

• Breastfeeding appears to protect infants from Giardia intestinalis

infection Breast milk contains detectable titers of secretory IgA, which is
protective for infants, especially in developing countries.

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Life cycle of G.lamblia

Morphology of Giardia cyst and trophozoite

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Giardia lamblia cyst in fecal smear

Giardia lamblia trophozoite under microscope