Flagellates: Intestinal and Extraintestinal Species

Giardia intestinalis

• Size: 8-20 μm long, 5-16 μm wide
• Shape: Pear-shape, teardrop, or falling leaf
• Motility: Falling leaf
• Nuclei: Two ovoid-shaped, each with a large karyosome
• Flagella: Four pairs, originating from anterior and posterior ends, and central extending laterally
• Other structures: Two median bodies, two axonemes, sucking disk, and four flagella (three extending from anterior end, one extending posteriorly from cytostome region)
• Appearance: Bilaterally symmetrical

Chilomastix mesnili

• Size: 5-25 μm long, 5-10 μm wide
• Shape: Pear-shaped
• Motility: Stiff, rotary, directional
• Nuclei: One with small central or eccentric karyosome
• Other structures: Prominent cytostome extending 1/3 to 1/2 body length, spiral groove, and no peripheral chromatin

Dientamoeba fragilis

• Size: 5-18 μm
• Shape: Irregularly round
• Motility: Progressive, broad hyaline pseudopodia
• Nuclei: Two, each consisting of massed clumps of four to eight chromatin granules
• Other structures: No peripheral chromatin

Trichomonas hominis

• Size: 7-20 μm long, 5-18 μm wide
• Shape: Pear-shaped
• Motility: Nervous, jerky
• Nuclei: One with small central karyosome
• Other structures: Three to five anterior flagella, one posterior extending from the posterior end of the undulating membrane, axostyle extending beyond the posterior, full body length undulating membrane, and conical cytostome cleft in anterior region

Enteromonas hominis

• Size: 3-10 μm long, 3-7 μm wide
• Shape: Oval; sometimes half-circle
• Motility: Jerky
• Nuclei: One with central karyosome
• Other structures: Four total flagella, three directed anteriorly, one directed posteriorly, and no peripheral chromatin

Retortamonas intestinalis

• Size: 3-7 μm long, 5-6 μm wide
• Shape: Ovoid
• Motility: Jerky
• Nuclei: One with small central karyosome
• Other structures: Ring of chromatin granules may be on nuclear membrane, two anterior flagella, and cytostome extending halfway down body length with well-defined fibril border

Trichomonas tenax

• Size: 5-14 μm long
• Shape: Oval, pear-shaped
• Motility: Nervous, jerky
• Nuclei: One ovoid nucleus; consists of vesicular region filled with chromatin granules
• Other structures: Five total flagella, all originating anteriorly, undulating membrane extending two thirds of body length with accompanying costa, thick axostyle curves around, and extends beyond body length, and bacteria-filled vacuoles common in cytoplasm

Trichomonas vaginalis

• Size: Up to 30 μm long
• Shape: Ovoid, round or pear-shaped
• Motility: Rapid, jerky
• Nuclei: One ovoid, nondescript
• Other structures: Three to five anterior flagella, one posterior, undulating membrane extending half of body length, prominent axostyle that often curves and around, and granules may be seen along axostyle

Cyst Characteristics

• Giardia intestinalis: 8-17 μm long, 6-10 μm wide, ovoid shape, immature cyst with two nuclei, mature cyst with four nuclei, central karyosomes, no peripheral chromatin, median bodies, and interior flagellar structures
• Chilomastix mesnili: 5- μm long, lemon-shaped, with a clear hyaline knob extending from the anterior end, one nucleus with large central karyosome, no peripheral chromatin

Flagellates

• Intestinal: Giardia intestinalis, Chilomastix mesnili, Dientamoeba fragilis, Trichomonas hominis, Enteromonas hominis, Retortamonas intestinalis
• Extraintestinal: Trichomonas vaginalis
• Common associated diseases: Giardia intestinalis - Giardiasis, traveler’s diarrhea; Chilomastix mesnili - None; Dientamoeba fragilis - Dientamoeba fragilis infection; Trichomonas hominis - None; Enteromonas hominis - None; Retortamonas intestinalis - IS: Cysts, DS: Cysts and trophozoites; Trichomonas vaginalis - Persistent urethritis, persistent vaginitis, infant Trichomonas vaginalis infection

Test your knowledge of flagellates, including Giardia intestinalis, Chilomastix mesnili, Dientamoeba fragilis, Trichomonas hominis, and Retortamonas intestinalis, and their associated diseases and characteristics.