Skip directly to search Skip directly to A to Z list Skip directly to site content
CDC Home
Share
Compartir
For questions about DPDx, contact us
DPDx

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

Diagnostic Procedures

Please choose from one of the categories below.

Stool Specimens

Intestinal Parasites: Comparative Morphology Tables

Table 1: Characteristics of Intestinal Amebae Visible in Different Types of Fecal Preparations

UNSTAINED TEMPORARY STAINS PERMANENT STAINS
Stage Characteristic Saline Formalin Iodine (Cysts) Buffered Methylene Blue1 (Trophs)
Trophozoites Motility +
Cytoplasm
Appearance + + + +
Inclusions (rbc., bacteria) + + + +
Nucleus +2 + +
Cysts Nuclei + + +
Chromatoid bodies + + +3 +
Glycogen + (vacuole present)
  1. Quensel's stain may be substituted for buffered methylene blue.
  2. Nuclei of trophozoites are visible in formalin-fixed material but are usually not sufficiently distinctive for species identification.
  3. Chromatoid bodies are more easily seen in unstained wet mounts than in iodine preparations.

Table 2: Characteristics of Intestinal Flagellates, Ciliate, and Coccidia Visible in Different Types of Fecal Preparations

Flagellates
UNSTAINED TEMPORARY STAINS PERMANENT STAINS
Stage Characteristic Saline Formalin Iodine (Cysts) Neutral Red1 (Trophs)
Trophozoites Motility + ­ + ­
Shape + + + +
(may be distorted)
Nucleus ­ + + +
Flagella ± ­ + ±
Other features2 + + + +
Cysts Shape + + + +
Nuclei ­ + + +
Fibrils ± + + +
Ciliate (Balantidium coli)
UNSTAINED TEMPORARY STAINS PERMANENT STAINS
Stage Characteristic Saline Formalin Iodine (Cysts) Neutral Red1 (Trophs)
Trophozoites Motility + ­ + ­
Macronucleus + + + +
Cilia + + + +
Cysts Macronucleus + + ± +
Coccidia
UNSTAINED TEMPORARY STAINS PERMANENT STAINS
Characteristic Saline Formalin Iodine (Cysts) Neutral Red1 (Trophs)
Oocysts/Sporocysts + + + ±3
  1. Neutral red dye in methocel solutions.
  2. The undulating membrane of Trichomonas and the spiral groove of Chilomastix may not be visible in all cases.
  3. Cryptosporidium oocysts can be demonstrated in acid-fast stains.

Table 3: Differential Morphology of Protozoa Found in Stool Specimens of Humans: Amoebae-Trophozoites

NUCLEUS CYTOPLASM
Species Size (Length) Motility Number Peripheral Chromatin Karyosomal Chromatin Appearance Inclusions
Entamoeba histolytica 10-60 µm. Usual range, 15-20 µm commensal form.1 Over 20 µm invasive form.2 Progressive with hyaline, finger-like pseudopods. 1
Not visible in unstained preparations.
Fine granules. Usually evenly distributed and uniform in size. Small, discrete. Usually centrally located, but occasionally is eccentric. Finely granular. Red blood cells occasionally. Noninvasive organisms may contain bacteria.
Entamoeba hartmanni 5-12µm. Usual range, 8-10 µm. Usually nonprogressive but may be progressive occasionally. 1
Not visible in unstained preparations.
Similar to
E. histolytica.
Small, discrete, often eccentric. Finely granular. Bacteria.
Entamoeba coli 15-50µm. Usual range, 20-25 µm. Sluggish, nonprogressive, with blunt pseudopods. 1
Often visible in unstained preparations.
Coarse granules, irregular in size and distribution. Large, discrete, usually eccentric. Coarse, often vacuolated. Bacteria, yeasts, other materials.
Entamoeba polecki 10-25µm. Usual range, 15-20 µm. Usually sluggish, similar to E. coli. Occasionally, in diarrheic specimens, motility may be progressive. 1
May be slightly visible in unstained preparations. Occasionally may be irregularly distorted by pressure from vacuoles in cytoplasm.
Usually fine granules evenly distributed. Occasionally granules may be irregularly arranged. Chromatin sometimes in plaques or crescents. Small, discrete, eccentric. Occasionally large, diffuse or irregular. Coarsely, granular, may resemble E. coli. Contains numerous vacuoles. Bacteria, yeasts.
Endolimax nana 6-12 µm. Usual range, 8-10 µm. Sluggish, usually nonprogressive with blunt pseudopods. 1
Visible occasionally in unstained preparations.
None. Large, irregularly shaped, blot-like. Granular, vacuolated. Bacteria.
Iodamoeba buetschlii 8-20 µm. Usual range, 12-15 µm. Sluggish, usually nonprogressive. 1
Not usually visible in unstained preparations.
None. Large, usually central. Surrounded by refractile, achromatic granules. These granules are often not distinct even in stained slides. Coarsely granular, vacuolated. Bacteria, yeasts, or other material.
Dientamoeba fragilis3 5-15 µm. Usual range, 9-12 µm. Pseudopods are angular, serrated, or broad lobed, and hyaline, almost transparent. 2
(In approximately 20% of organisms only 1 nucleus is present.) Nuclei invisible in unstained preparations.
None. Large cluster of 4-8 granules. Finely, granular. Bacteria: occasionally red blood cells.

Table 4: Differential Morphology of Protozoa Found in Stool Specimens of Humans: Amoebae-Cysts

NUCLEUS CYTOPLASM
Species Size (Diameter or Length) Shape Number Peripheral Chromatin Karyosomal Chromatin Inclusions Appearance
Entamoeba histolytica 10-20 µm
Usual range, 12-15 µm.
Usually spherical. 4 in mature cyst. Immature cysts with 1 or 2 occasionally seen. Peripheral chromatin present. Fine, uniform granules, evenly distributed. Small, discrete, usually centrally located. Present. Elongated bars with bluntly rounded ends. Usually diffuse. Concentrated mass often present in young cysts. Stains reddish brown with iodine.
Entamoeba hartmanni 5-10 µm
Usual range, 6-8 µm.
Usually spherical. 4 in mature cyst. Immature cysts with 1 or 2 often seen. Similar to E. histolytica. Similar to E. histolytica. Present. Elongated bars with bluntly rounded ends. Similar to E. histolytica.
Entamoeba coli 10-35 µm
Usual range, 15-25 µm.
Usually spherical. Occasionally oval, triangular, or other shapes. 8 in mature cyst. Occasionally super-nucleated cysts with 16 or more are seen. Immature cysts with 2 or more occasionally seen. Peripheral chromatin present. Coarse granules irregular in size and distribution, but often appear more uniform than in trophozoites. Large, discrete, usually eccentric but occasionally centrally located. Present, but less frequently seen than in E. histolytica. Usually splinter-like with pointed ends. Usually diffuse, but, occasionally well defined mass in immature cysts. Stain reddish brown with iodine.
Entamoeba polecki 9-18 µm
Usual range, 11-15 µm.
Spherical or oval. 1. Rarely 2. Occasionally visible in unstained preparations. Usually fine granules evenly distributed. Usually small and eccentric. Present. Many small bodies with angular or pointed ends, or few large ones. May be oval, rod-like, or irregular. Usually small, diffuse masses stain reddish brown with iodine. A dark area called an "inclusion mass" (possibly concentrated cytoplasm) is often also present. Mass stains lightly with iodine.
Endolimax nana 5-10 µm.
Usual range, 6-8 µm.
5-10 µm.
Usual range, 6-8 µm.
5-10 µm.
Usual range, 6-8 µm.
None. Large (blot-like), usually central. Occasionally granules or small oval masses seen, but bodies as seen in Entamoeba spp. are not present. Usually diffuse. Concentrated mass seen occasionally in young cysts. Stains reddish brown with iodine.
Iodamoeba buetschlii 5-20 µm. Usual range, 10-12 µm
Ovoidal, ellipsoidal, triangular, or other shapes. 1 in mature cyst. None. Large, usually eccentric. Refractile, achromatic granules on one side of karyosome. Indistinct in iodine preparations. Occasionally granules present, but chromatoid bodies as seen in Entamoeba spp. are not present. Compact, well-defined mass. Stains dark brown with iodine.

Table 5: Differential Morphology of Protozoa Found in Stool Specimens of Humans: Flagellates-Trophozoites

Species Size (Length) Shape Motility Number of Nuclei Number of Flagella* Other Features
Pentatrichomonas hominis 6-20 µm.
Usual range. 11-12 µm.
Pear shaped. Nervous, jerky. 1
Not visible in unstained mounts.
3-5 anterior.
1 posterior.
Undulating membrane extending length of body.
Chilomastix mesnili 6-24 µm.
Usual range, 10-15 µm.
Pear shaped. Stiff, rotary. 1
Not visible in unstained mounts.
3 anterior.
1 in cytosome.
Prominent cytostome extending 1/3-1/2 length of body. Spiral groove across ventral surface.
Giardia duodenalis 10-20 µm.
Usual range, 12-15 µm.
Pear shaped. "Falling leaf." 2
Not visible in unstained mounts.
4 lateral.
2 ventral.
2 caudal.
Sucking disk occupying 1/2-3/4 of ventral surface. Median bodies lying horizontally or obliquely in lower part of body.
Enteromonas hominis 4-10 µm.
Usual range,
8-9 µm.
Oval. Jerky. 1
Not visible in unstained mounts.
3 anterior.
1 posterior.
One side of body flattened. Posterior flagellum extends free posteriorly or laterally.
Retortamonas intestinalis 4-9 µm.
Usual range, 6-7 µm.
Pear shaped or oval. Jerky. 1
Not visible in unstained mounts.
1 anterior.
1 posterior.
Prominent cytostome extending approximately 1/2 length of body.

*Not a practical feature for identification of species in routine fecal examinations

Table 6: Differential Morphology of Protozoa Found in Stool Specimens of Humans: Flagellates-Cysts

Species Size (Length) Shape Number of Nuclei Other Features
Pentatrichomonas hominis No cyst.
Chilomastix mesnili 6-10 µm.
Usual range, 8-9 µm.
Lemon shaped with anterior hyaline knob. 1. Not visible in unstained preparations. Cytostome with supporting fibrils. Usually visible in stained preparations.
Giardia duodenalis 8-19 µm.
Usual range. 11-12 µm.
Oval or ellipsoidal. Usually 4. Not distinct in unstained preparations. Usually located at one end. Fibrils or flagella longitudinally in unstained cysts. Deep staining fibers or fibrils may be seen lying laterally or obliquely across fibrils in lower part of cyst. Cytoplasm often retracts from a portion of cell wall.
Enteromonas hominis 4-10 µm.
Usual range, 6-8 µm.
Elongated or oval. 1-4, usually 2 lying at opposite ends of cyst. Not visible in unstained mounts. Resembles E. nana cyst. Fibrils or flagella are usually not seen.
Retortamonas intestinalis 4-9 µm.
Usual range, 4-7 µm.
Pear shaped or slightly lemon shaped. 1. Not visible in unstained mounts. Resembles Chilomastix cyst. Shadow outline of cytostome with supporting fibrils extends above nucleus.

Table 7: Differential Morphology of Protozoa Found in Stool Specimens of Humans: Ciliates, Coccidia, and Blastocystis

Species Stage Size Shape Motility Number of Nuclei Other Features
Balantidium coli Trophozoite 50-70 µm or more. Usual range, 40-50 µm. Ovoid with tapering anterior end. Rotary, boring. 1 large, kidney shaped macronucleus. 1 small micronucleus immediately adjacent to macronucleus. Macronucleus occasionally visible in unstained preparations as hyaline mass. Body surface covered by spiral, longitudinal rows of cilia. Contractile vacuoles are present.
Cyst 45-65 µm. Usual range, 50-55 µm. Spherical or oval. 1 large macronucleus visible in unstained preparations as hyaline mass. Macronucleus and contractile vacuole are visible in young cysts. In older cysts, internal structure appears granular.
Cystoisospora belli Oocyst 25-30 µm. Usual range, 28-30 µm. Ellipsoidal Nonmotile Usual diagnostic stage is immature oocyst with single granular mass (zygote) within. Mature oocyst contains 2 sporocysts with 4 sporozoites each.
Sarcocystis hominis Sporocyst1 13-17 µm. Usual range, 14-16 µm. Oval Nonmotile Mature oocysts with thin wall collapsed around 2 sporocysts or free fully mature sporocysts with 4 sporozoites inside are usually seen in feces.
Sarcocystis suihominis Sporocyst1 1-15 µm.
Usual range, 12-13 µm.
Oval Nonmotile Mature oocysts with thin wall collapsed around 2 sporocysts or free fully mature sporocysts with 4 sporozoites inside are usually seen in feces.
Cryptosporidium Oocyst 3-6 µm.
Usual range, 4-5 µm.
Spherical or oval. Nonmotile Mature oocyst contains 4 "naked" sporozoites. No sporocysts are present.
Blastocystis hominis2 Vacuolated Form 5-30 µm.
Usual range, 8-10 µm.
Spherical, oval, or ellipsoidal Nonmotile 1, usually, but 2-4 may be present. Located in "rim" of cytoplasm. In binucleated organisms, the 2 nuclei may be at opposite poles. In quadrinucleated forms, the 4 nuclei are evenly spaced around periphery of cell. Cell contains large central body, or "vacuole" with a thin band, or "rim" of cytoplasm around the periphery. Occasionally a ring of granules may be seen in cytoplasm and the cell appears to have a "beaded rim."
  1. Sizes are based on information from Rommel and Heydorn (1972) and Heydorn et al. (1975).
  2. Description based on information from Zierdt, 1973 and McClure et al., (1980).

Table 8a (Nematodes): Differential Morphology of the Diagnostic Stages of Helminths Found in Humans: Eggs (Nematodes)

Species Size Shape Color Stage of Development When Passed Specific Features And Variations
Enterobius vermicularis 55 µm x 26 µm Range, 50-60 µm 20-32 µm. Elongated, asymmetrical with one side flattened, other side convex. Colorless. Embryonated. Contains C shaped or tadpole-like embryo. Smooth, thin eggshell with one flattened side. Occasionally may contain a fully developed larva. (More readily found on anal swabs than in feces).
Ascaris lumbricoides
fertile egg
60 µm x 45 µm. Range, 45-70 µm x 35-45 µm. Round or ovoidal. with thick shell. Brown or yellow brown. 1 cell, separated from the shell at both ends. Mammillated albuminous coat or covering on outer shell. Coat is sometimes lost and decorticated eggs have a colorless shell with gray or black internal material. Eggs may be in 2, 4, or more cells, or contain a fully developed larva.
Ascaris lumbricoides
infertile egg
90 µm x 40 µm. Range, 85-95 µm x 35-45 µm. Elongated, occasionally triangular, kidney shaped or other bizarre forms. Shell often very thin. Brown. Internal material is a mass of irregular globules and granules that fills shell. Mammillated covering attenuated or missing in many cases.
Trichuris trichiura 54 µm x 22 µm. Range, 49-65 µm x 20-29 µm. Elongated, barrel-shaped with a polar "plug" at each end. Yellow to brown. "Plugs" are colorless. 1 cell or unsegmented. Polar plugs are distinctive. Eggs occasionally are oriented in a vertical or slanted position and may not be readily recognized. A gentle tap on the coverslip will usually reorient the egg. On rare occasions, atypical eggs lacking polar plugs may be seen.
Ancylostoma duodenale 60 µm x 40 µm. Range, 57-76 µm x 35-47 µm. Oval or ellipsoidal with a thin shell. Colorless with grayish cells. 4- to 8-cell stage. Occasionally, eggs in advanced cleavage (16 or more cells) or even embryonated may be seen. Rhabditiform larvae may be present if the specimens are old. Species identification can not be made on eggs alone; therefore, eggs should be reported simply as hookworm.
Necator americanus 65 µm x 40 µm. Range, 57-76 µm x 35-47 µm. Oval or ellipsoidal with a thin shell. Colorless with grayish cells. 4- to 8-cell stage. Occasionally, eggs in advanced cleavage (16 or more cells) or even embryonated may be seen. Rhabditiform larvae may be present if the specimens are old. Species identification can not be made on eggs alone; therefore, eggs should be reported simply as hookworm.
Trichostrongylus species 90 µm x 40 µm. Range, 75-95 µm x 40-50 µm. Elongated with one or both ends more pointed than hookworm. Colorless with grayish cells. May be in advanced cleavage or morula stage. Egg resembles hookworm egg but is larger and more pointed at the ends.

Table 8b (Cestodes): Differential Morphology of the Diagnostic Stages of Helminths Found in Humans: Eggs (Cestodes)

Species Size Shape Color Stage of Development When Passed Specific Features and Variations
Taenia saginata Taenia solium 35 µm. Range, 31-43 µm. Spherical with thick striated shell. Walnut brown. Embryonated. 6-hooked oncosphere present inside a thick shell. Thick, striated shell. Eggs of T. solium and T. saginata are indistinguishable and species identification should be made from proglottids or scoleces. "Taenia" spp. should be reported if only eggs are found.
Hymenolepis nana 47 µm x 37 µm. Range, 40-60 µm x 30-50 µm. Oval. Shell consists of 2 distinct membranes. On inner membrane are two small "knobs" or poles from which 4 to 8 filaments arise and spread out between the two membranes. Colorless, almost transparent. Embryonated. 6-hooked oncosphere inside shell. Polar filaments.
Hymenolepis diminuta 72 µm. Range, 70-86 µm x 60-80 µm. Round or slightly oval. Striated outer membrane and thin inner membrane with slight poles. Space between membranes may appear smooth or faintly granular. Yellow. Embryonated. 6-hooked oncosphere inside shell. Resembles H. nana but lacks polar filaments. Poles are rudimentary and often hard to see.
Dipylidium caninum 35-40 µm. Range, 31-50 µm x 27-48 µm. Spherical or oval. 5-15 eggs (or more) are enclosed in a sac or capsule. Colorless. Embryonated. 6-hooked oncosphere inside shell. Eggs are contained in a sac or capsule which ranges in size from 58 µm to 60 µm x 170 µm. Occasionally capsules are ruptured and eggs are free.
Diphyllobothrium latum 66 µm x 44 µm. Range, 58-76 µm x 40-51 µm. Oval or ellipsoidal with an inconspicuous operculum at one end and a small "knob" at the other end. Yellow to brown. Unembryonated. Germinal cell is surrounded by a mass of yolk cells which completely fills inner area of shell. Germinal cell is usually not visible. Egg resembles hookworm egg but has a thicker shell and an operculum.

Table 8c (Trematodes): Differential Morphology of the Diagnostic Stages of Helminths Found in Humans: Eggs (Trematodes)

Species Size Shape Color Stage of Development When Passed Specific Features and Variations
Schistosoma mansoni 140 µm x 66 µm. Range, 114-180 µm x 45-73 µm. Elongated with prominent lateral spine near posterior end. Anterior end tapered and slightly curved. Yellow or yellow brown. Embryonated. Contains mature miracidium. Lateral spine. Found in feces; in rare cases, in urine also. Eggs are discharged at irregular intervals and may not be found in every stool specimen. Are rare in chronic stages of infection.
Schistosoma japonicum 90 µm x 70 µm. Range, 68-100 µm x 45-80 µm. Oval. Small lateral spine is often seen or may appear as a small hook or "knob" located in a depression in the shell. Yellow or yellow brown. Embryonated. Contains mature miracidium. Found in feces. Often coated with debris and may be overlooked.
Schistosoma haematobium 143 µm x 60 µm. Range, 112-170 µm x 40-70 µm. Elongated with rounded anterior end and terminal spine at posterior end. Yellow or yellow brown. Embryonated. Contains mature miracidium. Terminal spine. Found in urine, occasionally in feces. Egg often covered with debris.
Schistosoma intercalatum 175 µm x 60 µm. Range, 140-240 µm x 50-85 µm. Elongated with tapered anterior end and terminal spine. Sometimes "spindle-shaped." Yellow or yellow brown. Embryonated. Contains mature miracidium. Terminal spine long, slender with bent tip. Resembles S. haematobium egg except it is longer, is thinner, and has a longer spine. Found in feces. May have debris adhering to shell.
Schistosoma mekongi 69 µm x 56 µm* Range, 51-73 µm x 39-66 µm. Spherical. Small lateral spine, not always visible or may appear as a small "knob" in a depression in the shell. Yellow or yellow brown. Embryonated. Contains mature miracidium. Found in feces. Closely resembles S. japonicum egg except it is smaller. May be coated with debris.
Clonorchis sinensis 30 µm x l6 µm. Range, 27-35 µm x 11-20 µm. Small, ovoidal, or elongated with broad rounded posterior end and a convex operculum resting on "shoulders." A small "knob" may be seen on the posterior end. Yellow brown. Embryonated. Contains mature miracidium. Small size, operculum and "knob" on posterior end. Shell often is covered by adhering debris.
Opisthorchis spp. 30 µm x 12 µm. Range, 26-30 µm x 11-15 µm. Elongated with operculum on anterior end and pointed terminal "knob" on posterior end. Yellow brown. Embryonated. Contains mature miracidium. Lacks prominent shoulders characteristic of Clonorchis and has more tapered end.
Heterophyes heterophyes 28 µm x 15 µm. Range, 28-30 µm x 15-17 µm. Small, elongated or slightly ovoidal. Operculum. Slight "knob" at posterior end. Yellow brown. Embryonated. Contains mature miracidium. Resembles Clonorchis egg but with less distinct shoulders. Operculum is broader than in Clonorchis.
Metagonimus yokogawai 28 µm x 17 µm. Range, 26-30 µm x 15-20 µm. Small, elongated or ovoidal. Operculum. No "shoulders" at anterior end. Small "knob" often seen on posterior end. Yellow or yellow brown. Embryonated. Contains mature miracidium. Resembles Clonorchis and Heterophyes eggs. Shell is slightly thinner than Heterophyes. Operculum is broader than Clonorchis.
Paragonimus westermani 85 µm x 53 µm. Range, 68-118 µm x 39-67 µm. Ovoidal or elongate with thick shell. Operculum is slightly flattened and fits into shoulder area of shell. Posterior end is thickened. Egg often asymmetrical with one side slightly flattened. Yellow brown to dark brown. Unembryonated. Filled with yolk material in which a germinal cell is imbedded. Cells are irregular in size. Found in sputum, occasionally in feces. Resembles egg of D. latum but is larger, slightly asymmetrical and the operculum is smaller and flatter. The widest part of the Paragonimus egg is usually anterior to the center ; in a D. latum, the widest area is around the center.
Fasciola hepatica 145 µm x 80 µm. Range, 120-150 µm x 63-90 µm. Ellipsoidal, thin shell. Small, indistinct operculum. Yellow to light brown. Unembryonated. Filled with yolk cells in which an indistinct germinal cell is imbedded. Large size. Broadly oval eggs.
Fasciolopsis buski 140 µm x 80 µm. Range, 130-159 µm x 78-98 µm. Ellipsoidal, thin shell. Small, indistinct operculum. Yellow brown. Unembryonated. Filled with yolk cells in which an indistinct germinal cell is imbedded. Large size. Resembles F. hepatica egg and cannot be easily distinguished from Fasciola.

*Based on sizes of eggs in human fecal specimens reported by Harinasuta and Kruatrachue (1962) and Taylor and Moose (1971).

Table 9: Differential Morphology of the Diagnostic Stages of Helminths Found in Humans: Larvae

RHABDITIFORM LARVA (First Stage. Has bulbed esophagus.) FILARIFORM LARVA (Third Stage. Lacks prominent bulb in esophagus.)
Species Size Genital Primordium Buccal Cavity Size Length of Esophagus Tip of Tail
Strongyloides stercoralis 225 mm × 16 mm. Range, 200- 300 mm × 16-20 mm. Prominent. Is an elongate, tapered, or pointed structure located along ventral wall about the body length. Short, about 1/3-1/2 as long as the width of the anterior end of the body. 550 mm × 20 mm. Range, 500-550 mm × 20-24 mm. Extends approximately 1/2 length of body. Notched.
Hookworm 250 mm × 17 mm. Range, 200- 300 mm × 14-17 mm. Inconspicuous. Rarely distinct. When seen, is small, located nearer the tail than that of Strongyloides. Long. Approximately as long as the width of the body. 500 mm. Range, 500-700 mm × 20-24 mm. Extends about 1/4 1ength of body. Pointed.

Table 10: Differential Morphology of the Diagnostic Stages of Helminths Found in Humans: Tapeworm Gravid Proglottids

Species Size Appearance of Uterus Other
Taenia solium 12 mm in length x 5-7 mm wide. Central "stem" or trunk with 7-13 main lateral branches on each side. Usually on surface of fecal material. May be in short chains of 2-3 proglottids.
Taenia saginata 16-20 mm long × 5-7 mm wide. Central "stem" or trunk with 15-20 main lateral branches on each side. Usually on surface of fecal material. May be single detached proglottids.
Diphyllobothrium latum 2-4 mm long × 10-12 mm wide. Broader than long. Coiled into a rosette appearance. Occasionally, portion of worm may be passed. Egg is usual diagnostic stage.
Dipylidium caninum 12 mm long × 3 mm wide. Pumpkin-seed shape; tapers at each end. Uterus not visible. Proglottid filled with capsules containing eggs. Proglottids may be passed singly or in chains. Often resemble rice grains in stool.
Hymenolepis nana 0.2-0.3 mm long x 0.8-0.9 mm wide. Broader than long. Uterus not visible. Proglottid filled with eggs. Proglottids usually disintegrate in the intestinal tract and are rarely seen in stools. Egg is usual diagnostic stage.
Hymenolepis diminuta 0.7-0.8 mm long × 3-4 mm wide. Broader than long. Uterus not visible. Proglottid filled with eggs. Proglottids usually disintegrate in the intestinal tract and are rarely seen in stools. Egg is usual diagnostic stage.

Table 11: Differential Morphology of the Diagnostic Stages of Helminths Found in Humans: Tapeworm Scoleces

Species Size Shape Suckers No. Appearance Other
Taenia solium Approximately 1 mm in diameter. Globular or rounded. 4 Cup-like. Double row of 25-30 large and small brown chitinous hooks arranged around a rostellum (small projection) at the top of the scolex.
Taenia saginata 1 to 2 mm in diameter. Rounded or slightly pyriform. 4 Cup-like. Does not have a rostellum or hooks.
Diphyllobothrium latum 2 to 3 mm in length × 1 mm wide. Almond-shaped or spatulate. 2 Grooves. Does not have a rostellum or hooks. Deep grooves (suckers) are located dorsally and centrally on the scolex, but often appear to be lateral.
Dipylidium caninum 0.35 × 0.37 mm. Rhomboid or rounded. 4 Oval, cup-like. Prominent conical or ovoid rostellum with 30-150 small thorn-shaped hooks arranged in several rows (1-7 rows). Rostellum may be retracted into a depression at the upper margin of the scolex.
Hymenolepis nana 0.3 mm in diameter. Globular. 4 Cup-like. Retractile rostellum with a single row of 20 to 30 hooks.
Hymenolepis diminuta 0.2-0.4 mm in diameter. Globular or club-shaped. 4 Cup-like. Rudimentary apical rostellum without hooks.


Intestinal Parasites: Comparative Morphology Figures

Figure 1: Protozoa Found in Stool Specimens of Humans: Amebae

Scale for 10 micro meters
Stage Entamoeba histolytica/dispar Entamoeba hartmanni Entamoeba coli Entamoeba polecki Endolimax nana Iodamoeba beutschlii
Trophozoite Entamoeba histolytica/dispar trophozoite Entamoeba hartmanni trophozoite Entamoeba coli trophozoite Entamoeba polecki trophozoite Endolimax nana trophozoites Iodamoeba beutschlii trophozoite
Cyst Entamoeba histolytica/dispar cyst Entamoeba hartmanni cyst Entamoeba coli cyst Entamoeba polecki cyst Endolimax nana cyst Iodamoeba beutschlii cyst
Entamoeba histolytica/dispar cyst Entamoeba hartmanni cyst Entamoeba coli cyst Entamoeba polecki cyst Endolimax nana cyst Iodamoeba beutschlii cyst

Figure 2: Protozoa Found in Stool Specimens of Humans: Ciliates and Flagellates

Stage Ciliate 40 micrometer scale40 µm Flagellates 10 micrometer scale10 µm
Balantidium coli Chilomastix mesnili Giardia duodenalis Dientamoeba fragilis
Trophozoite Balantidium coli trophozoite Chilomastix mesnili trophozoite Giardia duodenalis trophozoite Dientamoeba fragilis
Cyst Balantidium coli cyst Chilomastix mesnili cyst Giardia duodenalis cyst no cyst stage
Chilomastix mesnili cyst Giardia duodenalis cyst

Figure 3: Protozoa Found in Stool Specimens of Humans: Coccidia and Blastocystis

Scale for 10 micro meters
Coccidia Blastocystis
Cystoisospora belli Sarcocystis spp. Cryptosporidium spp. Cyclospora cayetanensis Blastocystis hominis
Cystoisospora belli wet mount wet mount Sarcocystis oocyst oocyst Cryptosporidium in wet mount wet mount Cyclospora cayetanensis wet mount wet mount Blastocystis hominis wet mount wet mount
Cystoisospora belli safranin stain safranin Sarcocystis oocyst sporocyst sporocyst Cryptosporidium in acid fast acid-fast Cyclospora cayetanensis acid-fast acid-fast Blastocystis hominis trichrome stain trichrome

Figure 4: Nematode and Cestode Eggs Found in Stool Specimens of Humans

Nematodes Capillaria philippinensis egg Capillaria philippinensis Enterobius vermicularis egg Enterobius vermicularis Trichuris trichiura egg Trichuris trichiura Ascaris lumbricoides fertile egg Ascaris lumbricoides
fertile
Ascaris lumbricoides infertile egg Ascaris lumbricoides
infertile
Hookworm egg Hookworm Trichostrongylus egg Trichostrongylus spp.
Cestodes Taenia egg Taenia spp. Hymenolepis nana egg Hymenolepis nana Hymenolepis diminuta egg Hymenolepis diminuta Diphyllobothrium latum egg Diphyllobothrium latum Dipylidium caninum egg packet Dipylidium caninum
50 micrometer scale

Figure 5: Trematode Eggs Found in Stool Specimens of Humans

Trematodes100 micrometer scale 100 µm
Clonorchis sinensis egg Clonorchis sinensis Opisthorchis viverrini egg Opisthorchis viverrini Paragonimus westermani egg Paragonimus westermani1 Nanophyetus salmincola egg Nanophyetus salmincola
Schistosoma japonicum egg Schistosoma japonicum Schistosoma mekongi egg Schistosoma mekongi Schistosoma mansoni egg Schistosoma mansoni Schistosoma intercalatum egg Schistosoma intercalatum
Schistosoma haematobium egg Schistosoma haematobium2 Fasciola hepatica egg Fasciola hepatica Fasciolopsis buski egg Fasciolopsis buski Echinostoma egg Echinostoma spp.
  1. Usually found in respiratory specimens.
  2. Usually passed in urine.

Figure 6: Relative Sizes of Helminth Eggs

Measurements in micrometers (µm)

Images of Opisthorchis viverrini, Clonorchis sinensis, Capillaria philippinensis, Taenia spp. and Hymenolepis nana  along a scale for reference. Images of Trichuris trichiura, Enterobius vermicularis, Ascaris lumbricoides fertile egg, Hookworm ,and Diphyllobothrium
latum along a scale for reference. Images of Hymenolepis diminuta, Trichostrongylus spp., Nanophyetus salmincola, Paragonimus westermani, and an infertile egg of Ascaris lumbricoides along a scale for reference. Images of Dipylidium caninum, Echinostoma spp., Fasciolopsis buski, and Fasciola hepatica along a scale for reference. Images of various Schistosoma species along a scale for reference.

Figure 7: Hookworm and Strongyloides Larvae

Rhabditiform (L1) Stage Filariform (L3) Stage
Rhabditoid larvae of Strongyloides and hookworm Filariform larvae of Strongyloides and hookworm
100 micrometer scale

Figure 8: Gravid Proglottids and Scoleces of Cestode Parasites of Humans

Note: figures are not shown to scale.

Taenia solium proglottid Taenia solium scolex

Taenia solium

Taenia saginata proglottid Taenia saginata scolex

Taenia saginata

Diphyllobothrium latum Diphyllobothrium latum

Diphyllobothrium latum

Dipylidium caninum proglottid Dipylidium caninum scolex

Dipylidium caninum

Hymenolepis nana proglottid Hymenolepis nana scolex

Hymenolepis nana

Hymenolepis diminuta proglottid Hymenolepis diminuta scolex

Hymenolepis diminuta

Figure 9: Adult Visceral Trematodes of Humans

Heterophyes heterophyes

Heterophyes heterophyes

Metagonimus yokogawai

Metagonimus yokogawai

Opisthorchis felineus

Opisthorchis felineus

Opisthorchis viverrini

Opisthorchis viverrini

Clonorchis sinensis

Clonorchis sinensis

Dicrocoelium dendriticum

Dicrocoelium dendriticum

Fasciola hepatica

Fasciola hepatica

Paragonimus westermani

Paragonimus westermani

Echinostoma revolutum

Echinostoma revolutum

Key
  • AC=acetabulum (ventral sucker)
  • CE=cecum
  • CL=collar
  • CS=cirrus sac
  • EB=excretory bladder
  • EG=eggs (within uterus)
  • ES=esophagus
  • GA=genitoacetabulum
  • IN=intestine
  • OS=oral sucker
  • OV=ovary
  • PH=pharynx
  • SR=seminal receptacle
  • TE=testes
  • UT=uterus
  • VT=vitellaria
 
For questions about DPDx, contact us
  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
  • Notice: Linking to a non-federal site does not constitute an endorsement by HHS, CDC or any of its employees of the sponsors or the information and products presented on the site.
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Rd. Atlanta, GA 30333, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO