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Table of Contents > Protozoans > Flagellates > Giardia lamblia morphology > Giardia lamblia artifacts

Giardia lamblia

Giardia trophozoite
Phase contrast x 400

Giardia rarely poses diagnostic difficulties when either the cyst or trophozoite stage is found.

Difficulty may stem from the following:

  • the organism may be difficult to detect in some clinical cases
  • the reader may be inexperienced
23 - Giardia lamblia

24 - Giardia lamblia

In wet mounts, cysts show the typical ovoid ellipsoid shape measuring from 8-19 mm, the usual range being 11-14 mm.


Mature cysts have four nuclei while the immature have two. Note the varying degree of clarity shown in these figures. It is possible to identify 2 nuclei, axonemes, and the median bodies in these wet mounts. 25 -  Giardia lamblia

26 - Giardia lamblia cyst

Giardia can either be dark or clear as shown in these figures.

Also, the cytoplasm of the cysts may retract from the cyst wall in formalin preserved specimens (left) making identification problematic.

Giardia trophozoites can also be visible in unstained preparations. The flagella are not visible in this figure.

Please note that this is a dark Giardia.

23 - Giardia lamblia trophozoites

43 - Giardia lamblia trophozoite

Giardia trophozoite
Trichrome stain x 1000

In the trichrome stain, the trophozoites exhibit the typical pyriform shape and contain two anteriorly placed nuclei, one on either side of the longitudinally axonemes.

The nuclei in the organisms contain centrally located karyosomes.

The dark-staining median bodies can also be seen below the nuclei.


The relative position of the nuclei and the median body gives the organism the typical "monkey face". Flagella are rarely seen in stain preparation because they stain poorly, although they are quite evident in this figure.

Giardia lamblia
Trichrome stain x 1000

Note the varying degrees of clarity in this figure. Although mature cysts usually have four nuclei only two are visible in these organisms.

Note the halo around the organism due to shrinkage of the cysts in the fixation process.

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