Diagnostic Findings [Last Modified: ]
[Giardia intestinalis (syn. Giardia lamblia)]
Causal Agent Life Cycle Geographic Distribution Clinical Features Laboratory Diagnosis Treatment

Microscopy

Cysts
Giardia intestinalis cysts are oval to ellipsoid and measure 8-19 µm (average 10-14 µm).  Mature cysts have 4 nuclei, while immature cysts have two.  Nuclei and fibrils are visible in both iodine-stained wet mounts and trichrome-stained smears.

G. intestinalis cyst in a wet mount G. intestinalis cyst in a wet mount
A B

A, B: G. intestinalis cysts in a wet mount stained with iodine.

G. intestinalis cysts stained with trichrome G. intestinalis cyst stained with trichrome
C D

C, D, E, F: G. intestinalis cysts stained with trichrome.  Sometimes the cytoplasm of the cyst may retract from the cell wall; this is visible in Image F.

G. intestinalis cyst stained with trichrome G. intestinalis cyst stained with trichrome
E F

Trophozoites
Giardia intestinalis trophozoites are pear-shaped and measure 10-20 micrometers in length.  In permanent, stained specimens, 2 large nuclei are usually visible.  The sucking disks (used for attaching to the host’s mucosal epithelium), median bodies, and flagella (8) may also be seen.

G. intestinalis trophozoite in a wet mount G. intestinalis trophozoite stained with trichrome
G H

G:  G. intestinalis trophozoite in a wet mount stained with iodine.
H: G. intestinalis trophozoite stained with trichrome.

G. intestinalis trophozoite stained with trichrome
I

I: G. intestinalis trophozoite stained with trichrome.

Giardia intestinalis cysts and C. parvum oocysts - IFA
J

J: Cysts of Giardia intestinalis (lower right) and oocysts of C. parvum (upper left) labeled with commercially available immunofluorescent antibodies.

 
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