Giardia lamblia
Source: http://soils.cses.vt.edu
Dr. Bimal Kumar Das
Department of Microbiology
All India Institute of Medical Scinces
New Delhi-29
The genus Giardia belongs to the class Zoomastigophorea, the
order Diplomonadida, and the family Hexamitidae.
It is one of the most primitive eukaryotes: it has a small subunit
ribosomal RNA sequence and no mitochondria and Golgi
apparatus
Now Giardia can be classified according to antigen, isoenzyme,
and genetic analysis in addition to their morphology and host
range.
G. lamblia (also called intestinalis or duodenalis) is the species
infecting humans.
Species identified
Giardia lamblia (intestinalis, duodenalis) - humans,
mammals
Giardia muris - mammals
Giardia ardeae - birds
Giardia psittaci - birds
Giardia agilis - amphibians
Cysteine-rich surface protein termed the variant
specific surface protein responsible for antigenic
variation within species
These proteins may help to protect the parasite against
the activity of intestinal proteases, as well as play a role
in immune evasion.
Of the Giardia species, only G. lamblia has been successfully
cultured in vitro.
The trophozoite divides by longitudinal binary fission
Two morphological forms: Trophozoite and cyst ( infective form)
Source: www.sd01.k12.id.us
Tear drop shaped
2 adhesive discs,
2 median bodies,
2 nuclei
4 pairs of flagella
intracytoplasmic projections axonemes
Source: http://medlib.med.utah.edu
two nuclei, each with a prominent
central karyosome (characteristic
facelike image )
Source: Gallery of histology Woods and Ellis2000
Haematoxilyn staining
four pairs flagellae
a flat ventral surface
sucking or adhesive disk
8 to 12 mm long and 7 to 10 mm wide
Source: http://soils.cses.vt.edu
convex dorsal surface
Epidemiology
Presumed to be zoonotic, but new evidence indicates that
strains may be species specific.
Host can be humans, primates, cats, dogs, calves,
beavers, rabbits, etc.
World wide distribution
Highest incidence in children, young adults in late summer.
Transmission
Person to person transmission
Water sports, surface contamination. Watershed
contamination
sexually active male homosexuals and persons in custodial
institutions.
Pathogenesis and Immune response (1)
•The production of diarrhea, and occasionally malabsorption, is
the result of a complex interaction of Giardia with the host,
•Infection occurs after oral ingestion of as few as 10 to 25
cysts.
•After excystation, trophozoites colonize and multiply in the
upper small bowel
•Adherence of G. lamblia in the human gut may be via the disk,
but may also involve specific receptor-ligand interactions
Pathogenesis and Immune response (2)
Several pathogenic mechanisms have been postulated
Disruption of the brush border
Mucosal invasion
Elaboration of an enterotoxin
Stimulation of an inflammatory infiltration leading to fluid and
electrolyte secretion and occasionally to villous changes
Source: Gallery of histology Woods and Ellis2000
Ventral sucking disc
TEM micrograph showing the method of attachment to
the duodenal wall.
Source: Gallery of histology Woods and Ellis2000
Giardia Lamblia clinging to the wall of a duodenal villus.
Immune Response
Partially protective immunity may develop to Giardia
Immune response involves both cellular and humoral immunity
Ig A, serum Ig G and Ig M are detected in patients: role of Ig A
is not completely understood, probably inhibits trophozoite
attachment
IgA deficiency lead to chronic giardiasis
Cell mediated immune response may also play a role
Human milk may also play a role in protection of the host against
Giardia : Free fatty acids and IgA antibodies
Infection with G. lamblia includes
asymptomatic cyst passage (5 to 15% )
•acute self-limited diarrhea (25 to 50% )
•and a chronic syndrome of diarrhea
•malabsorption, and weight loss
Symptomatic giardiasis is characterized by
•acute onset of diarrhea,
•abdominal cramps, bloating, and flatulence
•feelings of malaise, nausea, and anorexia
•may complain of sulfuric belching
•Vomiting, fever, and tenesmus occur less commonly.
•stools may be profuse and watery, but later they are
commonly greasy, and foul-smelling and may float
The role that chronic infection with Giardia
plays in the growth and development of
children in the developing world has been
controversial
Life Cycle
Trophozoites : Lives in duodenum, jejenum and upper ileum
They come in close contact to the mucosal, but do not invade
the host. Adhesive disc fits over surface of epithelial cell
The flagella act as a pump to move nutrients away from the
microvilla and hold the adhesive disc near the mucosa.
Rapid division to produce large numbers quickly
Source: Doug Allington
14 billion parasites in diarrheic stool (trophozoites only)
Moderate infection: 300 million cysts.
As the organism traverses the colon it is stimulated to encyst.
Produce an oval cyst with thick walls, with 2-4 nuclei.
Dividing within cyst (4 nuclei is older cyst)
Complete division in duodenum of host after ingestion
Cyst is approximately 8-10m and ellipsoid in shape.
The cyst is the infective state and is transferred by the fecaloral route.
Diagnosis
• Giardia should be identified 50 to 70% of the time after one stool,
and 90% identification after three stools
• Wet, saline mounts: falling leaf motion, fibrils present, and
nucleic characteristics.
• Biopsy tissue/duodenal aspirate stained by trichrome or Giemsa
stain.
• Enzyme immunoassay and fluorescent-anitbody monoclonal
antigen detection systems
• Sensitivity & specificity: 90-100%
( ProSpec T, GiardEIA, MeriFluor, Color Vue, and DD System)
Source: http://soils.cses.vt.edu
Source: Doug Allington
Source: Doug Allington
Source: http://www. cbc.ca
Drug
Adult
Pediatric
Metronidazole
250mgtidX 5-7 d
5mg/kg/tid x 7 d
Quinacrine
100mgtidX5-7d
2mg/kg tidX7d
Furazolidone
100 mg qid × 7–10 d
Paromomycin
25–30 mg/kg/d in 3 doses × 5–10 d
Tinidazole
2 g × 1 dose
2 mg/kg qid × 10
PREVENTION
The prevention of giardiasis requires proper handling and
treatment of water
Good personal hygiene on an individual basis
Chlorination alone is sufficient to kill G. lamblia cysts, important
variables, such as water temperature, clarity, pH, and contact
time, alter the efficacy of chlorine, and higher chlorine levels (4 to
6 mg/liter) may be required.
Bringing water to a boil is sufficient to kill all protozoal cysts; at
high altitudes, boiling for longer periods may be necessary
Artistic impression by Russel Kightley
Source: http://soils.cses.vt.edu