Introduction
Chilomastix mesnili is cosmopolitan in distribution although found more frequently in warm climates. It is thought to be non-pathogenic although the trophozoite has been associated with diarrheic stool. This is the largest flagellate found in man with an incidence of 1-10% being in the large intestine.
Chilomastix mesnili life cycle
Morphology of the Trophozoite
The trophozoites of C. mesnili are pear shaped and measure 6-20μm in length. They have one large nucleus with a small karyosome and three flagella that extend from the nucleus at the anterior end of the parasite. A distinct oral groove or cytosome can be seen near the nucleus with its sides being supported by two filaments. They are known to move in a directional manner.
Chilomastix mesnili. Iodine stain
Chilomastix mesnili trophozoites
Chilomastix mesnili trophozoite (pointed end)
Morphology of cysts
The cysts are 6-9μm; they have a large single nucleus with a large karyosome. They also have a prominent side knob giving it a characteristic lemon shape. The cytosome is evident with a curved shepherds crook fibril. It also has a characteristically coiled filament which when stained is darker in color.
Chilomastix mesnili cysts Iodine stain
Chilomastix mesnili cyst (lugol)
Chilomastix mesnili cyst
Chilomastix mesnili – cyst in an unstained concentrate
Chilomastix mesnili cysts shape
Laboratory Diagnosis
The characteristic lemon shaped cysts can be seen in a formol-ether concentrate. Motile organisms can be seen in a wet preparation of a fresh stool however the characteristic morphology is evident in a permanently stained preparation. Table 3-1 details useful morphological features that are similar between species of flagellate and are used in laboratory diagnosis.
References:
– CDC
– www.atlas-protozoa.com
