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Morphology of Diagnostic Stages of Intestinal Parasites of Humans*

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Morphology of Diagnostic Stages of Intestinal Parasites of Humans* MORPHOLOGY OF DIAGNOSTIC STAGES OF INTESTINAL PARASITES OF HUMANS* M. M. Brooke, Sc.D. D. M. Melvin, Ph.D. Division of Laboratory Training and Consultation Laboratory Program Office Second Edition* 1984 Reprinted 1989 U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Public Health Service Centers For Disease Control Atlanta, Georgia 30333 HHS Publication No. (CDC) 89-8116 *Updated from the original printed version in 2001. ii PREFACE Although the morphology of the diagnostic stages of the intestinal parasites found in humans is described in many textbooks and manuals, it is not generally readily available in the average laboratory. The characteristics commonly used to distinguish species are tabulated and illustrated in this publication. Thus, the technologist performing parasitology examinations in public health and medical laboratories can quickly refer to them. The booklet is designed to assist the microscopist in identifying the organisms found, but it is not a substitute for the practical training in laboratory procedures and differentiation of species under the supervision of persons experienced in diagnostic parasitology. In this second edition, several species of flagellates, coccidia, and schistosomes have been added. Because of the increased number of drawings, those of the flagellates and of the ciliate and coccidia have been separated into two figures. We thank Mrs. Margery Borom and Miss Jean Ryan, formerly of the Centers for Disease Control (CDC), for preparing the original drawings of the organisms and Mr. Ed Biel, Chief, Publications, Graphics Section, CDC, for the revisions and additions. M. M. Brooke, Sc.D. Associate Director Division of Laboratory Training and Consultation Dorothy M. Melvin, Ph.D. Chief, Parasitology Training Section iii CONTENTS INTRODUCTION…………………………………………………………..…. vii PROTOZOA…………………………………...………………………………. 1 Amebae……………...…………………………………………………..…... 1 Flagellates……………………………………………………………..…….. 2 Ciliate………………………………………...………………………………. 3 Coccidia………………………………………...……………………………. 3 Blastocystis………….………………………...….…………………..……... 4 HELMINTHS………………………………...….…………………….……... 5 Nematodes……………………………………….………………........…….. 5 Cestodes……………………………………………….………….…………. 6 Trematodes.......….................................................................................. 6 TABLES 1. Characteristics of Intestinal Amebae Visible in Different Types of Fecal Preparations.…………………………….………………… 2 2. Characteristics of Intestinal Flagellates, Ciliate, and Coccidia Visible in Different Types of Fecal Preparations.………………………… 4 3. Differential Morphology of Protozoa Found in Stool Specimens of Humans: Amebae 3 - Trophozoites………………..……………………8 4. Differential Morphology of Protozoa Found in Stool Specimens of Humans: Amebae - Cysts………………………………………………..9 5. Differential Morphology of Protozoa Found in Stool Specimens of Humans: Flagellates - Trophozoites……………………..…………….10 6. Differential Morphology of Protozoa Found in Stool Specimens of Humans: Flagellates - Cysts…………………………………….…..….11 7. Differential Morphology of Protozoa Found in Stool Specimens of Humans: Ciliate, Coccidia, and Blastocystis………………………….12 8. Differential Morphology of Diagnostic Stages of Helminths Found in Humans: Eggs…………………………………………………….13 9. Differential Morphology of Diagnostic Stages of Helminths Found in Humans: Larvae………………………………………………… 18 10. Differential Morphology of Diagnostic Stages of Helminths Found in Humans: Tapeworm Gravid Proglottids………………………. 19 11. Differential Morphology of Diagnostic Stages of Helminths Found in Humans: Tapeworm Scoleces……………………..………….. 20 FIGURES 1. Protozoa Found in Stool Specimens of Humans-Amebae……..……..21 2. Protozoa Found in Stool Specimens of Humans-Flagellates….….…..22 3. Protozoa Found in Stool Specimens of Humans-Ciliate, Coccidia, Blastocystis………………… ………………………...…..……..23 4. Nematode and Cestode Eggs Found in Stool Specimens of Humans…………………………………..….……………..……………..24 5. Trematode Eggs Found in Stool Specimens of Humans……………...25 6. Relative Sizes of Helminth Eggs……………………………...………….26 7. Hookworm and Strongyloides Larvae…………….………..……………27 8. Gravid Proglottids and Scoleces of Cestode Parasites of Humans…………………………….……………….….…..…28 REFERENCES……………………………….……..………………………..…..29 v INTRODUCTION The diagnostic stages of intestinal parasites are differentiated on the basis of specific morphologic features that can be seen microscopically. The characteristics that are visible in different types of preparations are listed in tables 1 and 2; the characteristics commonly used to distinguish species are presented in tables 3-11 for the microscopist's ready reference. The descriptions, however, do not include all the morphologic characteristics of the various stages, and supplemental references may be needed in some cases. Although Dientamoeba fragilis is a flagellate (Camp et al., 1974; Honigberg, 1974), morphologically, it resembles the amebae. Therefore, in this manual it is included with the amebae to facilitate species identification. Several parasite species were added to this second edition. Drawings of the trophozoites and cysts of Enteromonas hominis and Retortamonas intestinalis were included with those of the other flagellates. Information on the coccidia** was updated, and both descriptions and diagrams of the diagnostic stages of Sarcocystis and Cryptosporidium were included. Blastocystis hominis, now identified as a protozoan, was also included in the tables and figures. Because of the increased number of drawings, diagrams of the flagellates and the ciliate and coccidia were separated into two figures. Also in this edition, two additional species of trematodes, Schistosoma mekongi and Schistosoma intercalatum, were described in the table of differential morphology of helminth eggs. Drawings of these eggs, however, were not included in the figures. Some of the parasites listed occur only infrequently or accidentally in humans; but, since their diagnostic stages may be confused with those of the more common organisms, they were included here. For example, Entamoeba polecki is rarely found in human feces; however, it closely resembles Entamoeba histolytica and Entamoeba coli, and microscopists unaware of its existence may mistake it for these species. Similarly, several helminth species of lower animals that occasionally parasitize humans are included. The diagnostic stages may be misidentified by inexperienced microscopists. For example, Trichostrongylus (Nematode) eggs may be confused with hookworm eggs, and Hymenolepis diminuta (Cestode) eggs may be confused with Hymenolepis nana eggs. The protozoa found in the mouth, Entamoeba gingivalis and Trichomonas tenax, were omitted from this manual, since the diagnostic stages of these parasites are not found in feces. Trichomonas vaginalis was not included because it is a parasite of the urogenital system rather than of the intestinal tract. Technical methods for examining specimens are presented in the manual "Laboratory Procedures for the Diagnosis of Intestinal Parasites" (Melvin and Brooke, 1982). The morphology of the intestinal parasites is described in many parasitology textbooks. Some of those which emphasize morphology of the diagnostic stages and have good illustrations are listed in the references. **At the time of this publication the coccidian parasite Cyclospora cayetanensis had not been classified. vii PROTOZOA The intestinal protozoa of humans belong to four groups: amebae, flagellates, ciliates, and coccidia. In addition to these, Blastocystis hominis now has been identified as a protozoan (Zierdt and coworkers, 1967,1973,1976, 1983). With the exception of the coccidia and Giardia lamblia (flagellate) which inhabit the small intestine, the protozoa live in the caecum and colon. The coccidia differ from the other protozoan species in being obligatory tissue parasites. Oocysts or sporocysts, passed in the feces, are the diagnostic stages. Organisms belonging to the three other groups have two stages, trophozoites and cysts, in their life cycle, except Dientamoeba fragilis and Trichomonas* hominis (flagellates), which have only a trophozoite stage. Both trophozoites and cysts are passed in feces and are diagnostic stages. The features listed in tables 3-7 are those commonly seen in fecal preparations and used for identifications. Features or structures that are difficult to see or are demonstrated only by special techniques are omitted. Not all of the characteristics listed, however, can be seen in a single type of preparation. The fecal preparations used to demonstrate protozoa are either wet mounts or permanently stained smears. Wet mounts may be unstained (saline or formalin) or stained (iodine, buffered methylene blue, Quensel's stain, merthiolate-iodine- formaldehyde [MIF], or other temporary stains). Iodine is primarily a cyst stain, and iodine preparations are usually routinely prepared in examining fecal specimens for protozoa. Buffered methylene blue and Quensel's stains are used to stain amebae trophozoites. Others, such as MIF, will stain both stages, but they may be less satisfactory for trophozoites than for cysts. Fecal smears may be permanently stained with hematoxylin, trichrome, chlorazol black, or other suitable stains. Scaled drawings of the intestinal protozoa are presented in figures 1-3. AMEBAE Characteristics used to distinguish species of intestinal amebae are as follows: Trophozoites Motility- progressive or nonprogressive. Cytoplasm Appearance-finely granular, coarsely granular, or vacuolated. Inclusions-erythrocytes, bacteria,
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