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Classification of Visceral Flagellates
- Phylum: Sarcomastigophora
- Subphylum: Mastigophora
- Class: Zoomastigophora
- Orders: Retortamonadida, Diplomonadida. Trichomonadida
Features of Order Retortamonadida
- •2 to 4 flagella - 1 turned posteriorly and associated with ventrally located cytosomal area
- cysts present
- Example: Chilomastix mesnili
Features of Order Diplomonadida
- •With 2 equal nuclei lying side by side
- 1 to 4 pairs of flagella
- Example: Giardia lamblia
Features of Trichomonadida
- •anterior tuft of flagella
- a stout median rod called the axostyle
- undulating membrane along the recurrent flagellum
- Cyst formation absent
- Trichomonids are commonly found in vertebrates and invertebrates (e.g. termites).
- 4 common human pathogens: Dientamoeba fragilis, Trichomonas tenax, T. vaginalis and T. (Pentatrichomonas) hominis
- infects ~ 4% of the US and 6% of the world
- lives in LI of humans, primates, other vertebrates & invertebrates
- Trophozoite: pyriform (pear shaped)
- 12 µm long (range 5-20 µm)
- It has a blunt anterior end with 3 free flagella
- A 4th flagellum is located near the anterior end, so is the large nucleus
- Cyst stage occurs (trophozoite cannot withstand the host’s gastric juices).
- Cysts: uni-nucleated, thick walled, ~ 8 µm, and lemon-shaped
- Transmission: ingestion of cysts. Fecal contamination of drinking water is the most important means of transmission
- Although nonpathogenic, they may cause diarrhea
Giardia lamblia (intestinalis) Morphology
- discovered in 1681 by Leeuwenhoek
- Trophozoite: is rounded at the anterior, tapered posteriorly, and flattened dorso-ventrally
- It is about 12-15 µm in length
- flattened ventral surface bears a concave, bi-lobed adhesive disc with a nucleus in the center of each half. The disc is a rigid structure supported by microtubules
- 4 pairs of flagella: arise from basal bodies between the 2 nuclei
- 1 pair extends down the cell’s midline & emerge posteriorly as trailing flagella; ventral pair emerges at posterior edge of the adhesive disc
- Of the remaining 2 pairs, 1 emerges anteriolaterally and 1 laterally
- A pair of large, curved, transverse, dark-stained median bodies of unknown function lies behind the adhesive disc
- Cyst: 4 nuclei, remnants of median bodies and ventral groove, ovoid shape
Giardia lamblia Life Cycle
- Trophozoites: divide by binary fission. First the nuclei divide, then the locomotory apparatus and the sucking disc, and finally the cytoplasm. In the small intestine and in watery stools, only the trophic stage can be found.
- Cysts: form as the feces enter the colon & begin to dehydrate.
- The flagella shorten, cytoplasm condenses and secretes a thick, hyaline cyst wall.
- 10-12 µm in length
- Newly formed cysts have 2 nuclei, but older ones have 4.
- Soon the sucking disc and the locomotor apparatus are doubled, and the Siamese-twinned flagellates are ready to emerge
- When cysts are swallowed by the host, they pass safely through the stomach and excyst in the duodenum. The flagella grow out, and the parasites are once again at home
Giardia lamblia Life Cycle Image