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Chapter 3 : Intestinal Protozoa: Flagellates and Ciliates
This chapter begins with a discussion on Giardia lamblia. Recent studies document antigenic variation with surface antigen changes during human infections with G. lamblia; although the biological importance of this work is not clear, it suggests that this variation may provide a mechanism for the organism to escape the host immune response. Routine stool examinations are normally recommended for the recovery and identification of intestinal protozoa. A new and simple colorimetric method has been determined for determining in vitro activity against G. lamblia. Most experts agree that the single most effective practice that prevents the spread of infection in the child care setting is thorough handwashing by the children, staff, and visitors. Currently, the most commonly used method for examining purified material for protozoa is an antibody-based immunofluorescence assay. Isolates from asymptomatic individuals were found in the same zymodemes (isoenzyme groups) as were isolates from symptomatic hosts. The chapter next focuses on Dientamoeba fragilis. Since there is no known cyst stage, this organism will not be seen on a wet preparation. Consequently, it is mandatory that a permanent stained smear be included in the ova and parasite examination. Current recommendations include iodoquinol, paromomycin, or tetracycline. Since symptomatic relief has been observed to follow appropriate therapy, Dientamoeba fragilis is probably pathogenic in infected individuals who are symptomatic. Finally, the chapter focuses on Pentatrichomonas hominis, Chilomastix mesnili, Enteromonas hominis, Retortamonas intestinalis, and Balantidium coli.
Life cycle of Giardia lamblia.
Giardia lamblia trophozoites on the mucosal surface. (Scanning electron micrographs courtesy of Marietta Voge.)
(1) Trophozoite of Giardia lamblia (front view); (2) trophozoite of G. lamblia (side view); (3) cyst of G. lamblia; (4) trophozoite of Pentatrichomonas hominis; (5) trophozoite of Dientamoeba fragilis (two fragmented nuclei); (6) trophozoite of D. fragilis (one fragmented nucleus); (7) trophozoite of Chilomastix mesnili; (8) cyst of C. mesnili; (9) trophozoite of Enteromonas hominis; (10–12) cysts of E. hominis; (13) trophozoite of Retortamonas intestinalis; (14 and 15) cysts of R. intestinalis. (Illustrations by Sharon Belkin.)
(A to D) Trophozoites of Giardia lamblia; (E and F) cysts of G. lamblia.
Giardiasis. Fecal immunoassay kits can be used on human stool specimens to confirm the presence of Giardia spp. Currently available reagents can be used with fresh, frozen, or preserved specimens (not those containing polyvinyl alcohol). If fluorescent testing is performed, the specimen should not be frozen (the actual organisms are disrupted during the freeze-thaw cycle); however, fresh or preserved specimens are acceptable. Check with each manufacturer for compatibility of the fixative with the proposed test; not all fixatives are compatible with all types of fecal immunoassays.
Life cycle of Dientamoeba fragilis.
Trophozoites of Dientamoeba fragilis. (Illustration by Sharon Belkin.)
(A, B) Trophozoites of Dientamoeba fragilis. (A) The trophozoite contains a single nucleus fragmented into four parts; (B) the trophozoite contains two nuclei, both of which are also fragmented.
Life cycle of Pentatrichomonas hominis.
Life cycle of Trichomonas tenax.
Life cycle of Chilomastix mesnili, Enteromonas hominis, and Retortamonas intestinalis.
(A) Trophozoite of Chilomastix mesnili (note the feeding groove; flagella are not visible); (B) cyst of C. mesnili (note the “lemon or pear” shape and the curved fibril, the shepherd’s crook).
Life cycle of Balantidium coli.
(1) Trophozoite of Balantidium coli; (2) cyst of B. coli. (Illustration by Sharon Belkin.)
(A) Trophozoite of Balantidium coli (note the large bean-shaped macronucleus and evidence of cilia around the organism); (B) cyst of B. coli (note the large bean-shaped macronucleus).
Trophozoite of Balantidium coli in tissue. Note the cytostome (oral groove) and a portion of the macronucleus. The cilia are not clearly visible.
Giardia species a
Giardia genotypes a
Intestinal protozoa: trophozoites of flagellates
Intestinal protozoa: cysts of flagellates
Representative commercially available kits for immunodetection of Giardia lamblia
Recommendations for therapy for giardiasis a
Guidelines for hand washing
Questions for consideration when testing well water
Intestinal protozoa: ciliate
Intestinal flagellates and ciliates: recommended diagnostic procedures