Chapter 34 : Histologic Identification of Parasites

Amebic intestinal ulcers. (Upper) Intestinal ulcers; these may coalesce under the surface. (Lower) Note the “flask shape” (small opening on the mucosal surface and a larger area of destruction below the surface); the serosa is edematous and hyperemic. Multiple ulcers may develop and coalesce. Organisms would be found in the healthy tissue border, not in the necrotic material within the ulcer. (Courtesy of the CDC Public Health Image Library, Mae Melvin.) doi:10.1128/9781555819002.ch34.f1

Amebic intestinal ulcer. Entamoeba histolytica trophozoites in colon tissue (arrows); note the nucleus in each trophozoite (central karyosome); H&E stain (courtesy of the CDC Public Health Image Library). doi:10.1128/9781555819002.ch34.f2

Amebic intestinal ulcer. Entamoeba histolytica trophozoites in colonic ulcer, demonstrating a nucleus with tiny, centrally placed karyosome (arrow). Brown-Hopps stain (Armed Forces Institute of Pathology photograph). doi:10.1128/9781555819002.ch34.f3

Amebic lung section. Entamoeba histolytica trophozoites in lung tissue, PAS stain. Note the trophozoites are bright pink and can easily be seen. (Armed Forces Institute of Pathology photograph.) doi:10.1128/9781555819002.ch34.f4

Amebic liver abscess. (Upper) Gross image of liver abscess caused by Entamoeba histolytica. Note the sunken areas of the abscess. (Lower) Gross image of liver abscess, cut specimen. (Courtesy of the CDC Public Health Image Library, Mae Melvin.) doi:10.1128/9781555819002.ch34.f5

Acanthamoeba spp. (Upper) Cutaneous abscess on arm; nonhealing ulcer, possibly as a result of a human bite wound, that was not recognized as being caused by Acanthamoeba spp. Therapy with routine antibiotics was ineffective. (Courtesy of George Healy, Centers for Disease Control and Prevention.) (Lower) Acanthamoeba trophozoite (left), cyst (right). doi:10.1128/9781555819002.ch34.f6

Naegleria fowleri (primary amebic meningoencephalitis). (Upper) Cytospin of cerebrospinal fluid; note the trophozoite (arrow) with large karyosome (courtesy of the CDC Public Health Image Library). (Lower) Naegleria trophozoites in brain tissue; note the large karyosome (from A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman). doi:10.1128/9781555819002.ch34.f7

Balamuthia mandrillaris. (Upper) Trophozoites (circle) are seen in brain tissue. The amebae have the large, characteristic karyosome. The staining of the karyosome is much darker than that of the cytoplasm of the amebae. (Lower) Cyst in brain tissue. (Courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch34.f8

Sappinia pedata. Trophozoites (arrows) seen in brain tissue; note the presence of two nuclei within some of the trophozoites (arrow) where both are in the same plane of focus (courtesy of the CDC Public Health Image Library). doi:10.1128/9781555819002.ch34.f9

Giardia lamblia (duodenalis, intestinalis). (Top) Trophozoites in GI tract (circle). (Middle) Trophozoites on the surface of the duodenal mucosa (arrows) (Armed Forces Institute of Pathology photograph). (Bottom) Trophozoites in mucus from duodenal aspirate, Wheatley's trichrome stain. doi:10.1128/9781555819002.ch34.f10

Balantidium coli. Trophozoites in intestinal tissue; note dark macronucleus and evidence of the oral/feeding groove (arrow). doi:10.1128/9781555819002.ch34.f11

Toxoplasma gondii. (Upper) Cyst in brain tissue (bradyzoites). (Lower) Tachyzoites in bone marrow. doi:10.1128/9781555819002.ch34.f12

Sarcocystis spp. (Top) Sarcocyst in tissue. (Middle) Note the septa which are visible in this low-power image. Bradyzoites of Toxoplasma gondii in striated muscle resemble Sarcocystis spp. However, the Sarcocystis bradyzoites are usually more rounded at both ends, and they are contained in larger cysts than those of Toxoplasma. (Bottom) The Sarcocystis septa are visible, as are the crescentic spores. The sarcocyst wall varies from thin and smooth to thick and striated. Although sarcocysts may be confused with cysts of Toxoplasma, sarcocysts tend to be larger and contain larger bradyzoites. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f13

Intestinal villi. (Upper) Normal villi are long and slender. (Lower) Blunted villi, typical of histology seen with coccidial infections (Cryptosporidium spp., Cyclospora cayetanensis) (from reference 14 ). doi:10.1128/9781555819002.ch34.f14

Cryptosporidium spp. (Top) Organisms shown at the brush border (circle), developing in parasitophorous vacuoles and thus enclosed within membranes of host origin. The mucosal architecture tends to be abnormal, with marked shortening of the villi and hypertrophy of the crypts. (Middle) Organisms shown at the brush border (circle); thick epon section. (Bottom) Color-enhanced transmission electron micrograph showing Cryptosporidium (courtesy of the Science Photo Library, http://www.sciencephoto.com/media/445435/view). doi:10.1128/9781555819002.ch34.f15

Microsporidia. (Left) Spores in corneal lesion, PAS stain; note the dark-staining dot at the end of each spore. (Right) Spores in corneal lesion, silver stain; note spores appear to be outlined (1,000× oil immersion). Routine histologic testing can be performed by using tissue Gram stains or silver stains. Touch preparations can be methanol fixed and stained with Giemsa stain. Plastic-embedded tissues stained with PAS, silver, acid-fast, and routine H&E stains generally stain better than paraffin-embedded tissues. doi:10.1128/9781555819002.ch34.f16

Section of appendix showing Anncaliia connori spores in muscularis. The anterior end of the spore has a PAS-positive granule (arrows) (PAS, ×1,260). (Armed Forces Institute of Pathology photograph.) doi:10.1128/9781555819002.ch34.f17

Microsporidia in various stages of development in the intestinal enterocytes (1,000× oil immersion). When seen in stool, the spores measure approximately 1 to 3 μm. The microsporidia multiply extensively within the host cell cytoplasm; the life cycle includes repeated divisions by binary fission (merogony) or multiple fission (schizogony) and spore production (sporogony). Both merogony and sporogony can occur in the same cell at the same time. During sporogony, a thick spore wall is formed, providing environmental protection for this infectious stage of the parasite. Microsporidia are characterized by having spores containing a polar tubule, which is an extrusion mechanism for injecting the infective spore contents into host cells. To date, nine genera have been recognized in humans: Anncaliia, Brachiola, Encephalitozoon, Enterocytozoon, Pleistophora, Trachipleistophora, Vittaforma, Microsporidium, and Tubulinosema. doi:10.1128/9781555819002.ch34.f18

(Upper) Anncaliia connori spores in wall of ileum; 90-minute Grocott methenamine silver. (Lower) Anncaliia connori in myocardium; Ziehl-Neelsen. (Armed Forces Institute of Pathology photographs.) doi:10.1128/9781555819002.ch34.f19

Diagram of roundworm musculature morphology in tissue. (A) Polymyarian type. (B) Meromyarian type. (C) Homomyarian type. C, cuticle; DVC, dorsal-ventral chord; IN, intestine; LA, lateral alae; LC, lateral chord; M, muscle; OV, ovary. See . (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f20

Diagram through Loa loa (left, female; right, male) (polymyarian type of musculature). Note the well-developed muscle layer divided into four bands separated by the lateral, ventral, and dorsal chords. The muscle cells project into the body cavity. C, cuticle; DVC, dorsal-ventral chord; HY, hypodermis; IN, intestine; LC, lateral chord; M, muscle; SR, seminal receptacle; SV, seminal vesicle; UT, uterus. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f21

Diagram through Anisakis (left) and Baylisascaris procyonis (right) (polymyarian type of musculature). In Anisakis, note the well-developed muscular esophagus (ES) and the Y-shaped lateral chords (LC). In B. procyonis (brain tissue), one section is through the esophagus (ES) while the other is through the middle of the body, showing the excretory columns (EC), intestine (IN), and large lateral chords (LC). Note that the lateral alae (LA) are visible in each section. doi:10.1128/9781555819002.ch34.f22

Cross section of an adult male Ascaris lumbricoides. The section shows the outer protective cuticle secreted by the underlying hypodermis ( 1 ). Longitudinal muscle bands ( 2 ), dorsal and ventral nerve chords, lateral lines (containing the excretory canals), the intestine, and the pseudocoelom (body cavity) are also visible. The diagram also depicts various sections through the long, coiled testis ( 4 ) and vas deferens ( 3 ), the latter of which contains the ameboid spermatocytes (sperm cells). Note: These structures may differ in shape, depending on the way they were sectioned. ( 5 ) Lateral line with excretory canal; ( 6 ) intestine; ( 7 ) pseudocoelom. (Courtesy of the Department of Biology, University of Wisconsin-La Crosse, Rick Gillis and Roger J. Haro.) doi:10.1128/9781555819002.ch34.f23

Cross section of an adult female A. lumbricoides, stained with H&E. The hypodermis and musculature are visible below the cuticle. Note the presence of the prominent muscle cells (MU), gravid uterus (UT), intestine (IN), and coiled ovary (OV). (Courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch34.f24

Cross section of the cuticle of an adult A. lumbricoides, stained with H&E. Shown here are the cuticle (CU) and, immediately below the cuticle, the thin hypodermis (HY). Also shown are the prominent muscle cells (MU) and one of the lateral chords (LC). (Courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch34.f25

Baylisascaris procyonis. (Upper) CNS atrophy, sclerosis, and larval granuloma in the brain in a 2-year-old boy who died following 14 months of CNS problems. (Lower) B. procyonis larva (polymyarian type of musculature) and inflammation in the corpus callosum of an infected rabbit. Note the prominent alae (circle), excretory columns (oval), and multinuclear intestinal cells (arrow). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of K. R. Kazacos.) (See also Fig. 34.22 .) doi:10.1128/9781555819002.ch34.f26

Lagochilascaris (polymyarian type of musculature) encapsulated larvae in mouse lung tissue with varying degrees of damage, including secondary granuloma containing larvae in different degrees of destruction, concentric fibrosis, and foci of inflammatory infiltration composed of macrophages (H&E). (Courtesy of U.S. National Library of Medicine, National Institutes of Health.) doi:10.1128/9781555819002.ch34.f27

Toxocara. (Upper) Toxocara larva present in the eye (arrow). Eosinophil-rich vitreous abscess contains a fragment of a nematode larva (H&E). (Lower) Toxocara larva recovered in liver (visceral larva migrans). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f28

Anisakis cross section. Note the typical polymyarian type of musculature and the Y-shaped lateral chords (arrow). The large esophagus is in the center of the image (ES). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) (See also Fig. 34.22 .) doi:10.1128/9781555819002.ch34.f29

Dirofilaria sp. (Upper) Note the polymyarian type of musculature and the clearly delineated lateral chords. Also note the longitudinal ridges in the cuticle (bumpy appearance). (Lower) Higher magnification than upper image. Note the typical polymyarian type of musculature and the more clearly delineated longitudinal ridges on the inner surface of the cuticle (circle). The cuticle is relatively thick and multilayered. The very prominent lateral chords are also visible (LC), as is the lateral ridge (arrow); although ventral and dorsal chords are present, they are usually inconspicuous. (Courtesy of Marjorie R. Fowler and Andrea Linscott.) doi:10.1128/9781555819002.ch34.f30

Capillaria hepatica eggs in liver. These eggs resemble those of Trichuris trichiura, but the shells in Capillaria eggs are striated. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f31

Diagram through Enterobius vermicularis (both images are of females) (meromyarian type of musculature). Note the very conspicuous lateral alae (LA). The muscle cells (M) are large, of various shapes, and irregular; there are fewer cells per quadrant than seen in the polymyarian type ( Fig. 34.20 ). The lateral chords (LC), intestine (IN), ovary (OV), and uterus (UT) are also visible. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f32

(Upper) Longitudinal section of female Enterobius vermicularis in the cecum, H&E stain; note the esophageal bulb (arrow) (Korea Society for Parasitology, Sung-Jong Hong). (Lower) Intestinal lumen containing two transverse sections of an Enterobius vermicularis worm. This nematode has the meromyarian type of musculature. Note the lateral alae (circle) and intestine (arrow). (Armed Forces Institute of Pathology photograph.) doi:10.1128/9781555819002.ch34.f33

Cross section of adult Enterobius vermicularis female worm in the appendix. Note the characteristic football-shaped eggs (arrows). The lateral alae are also visible. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f34

Diagram through Trichuris trichiura (female on the left, male on the right) (homomyarian type of musculature). Note the very small, uniform muscle cells (M) with a regular arrangement, with many cells arranged in a complete circle. Note also the absence of lateral chords. The ejaculatory duct (EJ), intestine (IN), ovary (OV), oviduct (OVD), uterus (UT), and testis (TE) can also be seen. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f35

Colon heavily infected by Trichuris trichiura; photo taken during colonoscopy. (Courtesy of American Association for the Advancement of Science; reference 12 .) doi:10.1128/9781555819002.ch34.f36

Trichuris trichiura. (Upper) Several sections of adult male and female T. trichiura worms in the colon, showing the narrow anterior portion of the worm within the mucosa (“whip”) (arrows) and the thicker posterior portion (“handle”) free in the lumen (×15; Armed Forces Institute of Pathology photograph). (Lower) Cross section of female worm (I, intestine; OV, ovary; UT, uterus). The musculature is of the homomyarian type, with very small, uniform, regular cells with many cells in a complete circle. No lateral chords are present. (Courtesy of Andrea Linscott.) doi:10.1128/9781555819002.ch34.f37

Ancylostoma caninum. (Upper) Adult hookworm attached to the intestine (courtesy of Richard Bungiro, Yale University). (Lower) Hookworm; section of a worm attached to the mucosa. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f38

Hookworm. (Upper) Longitudinal section of an adult hookworm worm in a bowel biopsy, stained with H&E. Note the oral cavity (OC) and strong, muscled esophagus (ES). (Lower) Cross section of an adult hookworm from the same specimen in upper image. Shown here are the musculature (MU), intestine with brush border (IN), excretory ducts (ED), and coiled ovaries (OV). (Courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch34.f39

Trichinella spiralis. (Upper) Encysted larvae in muscle. Although Trichinella spp. have the homomyarian type of musculature, the magnification of this image is insufficient to show the details. (Lower) Squash preparation of tissue biopsy specimen. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f40

Diagram of a transverse section of a Taenia proglottid. Under the thick tegument, the underlying parenchyma is divided into cortical (CO) and medullary (ME) layers by a thick band of longitudinal muscles (M). The excretory columns (EC) are clearly visible. Branches of the uterus (UT) and testes (TE) are also seen. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f41

(Left) Diagram of a cysticercus of Taenia solium. The extensively folded spiral canal and a scolex with two large suckers are clearly visible. The denser tissue of the rostellum (between the two suckers) is also visible. In this particular section plane, the hooklets are not visible. Host tissue forms a fibrous capsule around the cysticercus. (Right) Diagram of a unilocular hydatid cyst of Echinococcus granulosus. The outer thick fibrous wall is visible (FW) and is produced by the host. Within the fibrous layer is the thinner laminated layer (LL), while right below that layer is the thin germinal epithelial layer (GL) from which daughter cysts and multiple protoscolices arise. Multiple protoscolices within a brood capsule are visible in this illustration. Note that the middle laminated layer is acellular and the thin germinal layer contains some calcareous corpuscles. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f42

Taenia solium cysticercus in pig muscle. The cysticercus consists of a fluid-filled bladder containing a single protoscolex. The cysticerci (T. solium) have a thick bladder wall, and the rostellum has two rows of hooklets (13 each). Each cysticercus measures 5 to 15 mm long by 4 to 12 mm wide. A convoluted spiral canal leads to the rostellum. The parenchyma usually contains calcareous corpuscles. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of P. M. Schantz.) doi:10.1128/9781555819002.ch34.f43

Taenia solium. (Upper) Subcutaneous nodule from a patient. (Lower) Higher magnification than upper figure; note the suckers (S). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of K. Juniper, Jr.) doi:10.1128/9781555819002.ch34.f44

Cysticercus. (Upper) Scolex of a cysticercus showing a sucker and hooklets of Taenia solium (circle); note the hooklets are barely visible. (Lower) Enlarged image of the hooklets within the cysticercus. (Armed Forces Institute of Pathology photographs.) doi:10.1128/9781555819002.ch34.f45

Taenia solium racemose cyst in the brain. (Upper) The bladder wall of the racemose cysticercus has three separate layers. The tegumental surface has wart-like protuberances and is acidophilic (T). Beneath the tegument are small, rounded, pyknotic nuclei (N). The innermost layer is made up of loose connective tissue (CT). (Lower) Higher magnification. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f46

Hymenolepis nana cysticerci in the villi of a mouse. (Top) When mature, these cysticerci (circle) emerge, attach to the intestinal wall, and develop into the adult worm (same life cycle seen in humans). (Middle) Note the curved suckers (green arrows) and hooklets (black arrow). (Bottom) Section through H. nana embedded in the mucosa. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of B. Gueft; specimen courtesy of M. Yoeli.) doi:10.1128/9781555819002.ch34.f47

(Upper) Echinococcus granulosus brood capsules (BC) arising from the germinal membrane (GM). The fibrinous wall of the host (W) and the laminated membrane (LM) are also seen. (Armed Forces Institute of Pathology photograph.) (Lower) Hydatid cyst; note the layers and brood capsules filled with protoscolices (circle) (courtesy of CDC Public Health Image Library, Peter Schantz). doi:10.1128/9781555819002.ch34.f48

Echinococcus granulosus. (Upper) Brood capsules (BC); the dark areas represent the hooklets on the protoscolices (circle). (Lower) Hooklets stained with the Ryan modified trichrome/blue. (Courtesy of Norbert Ryan.) doi:10.1128/9781555819002.ch34.f49

Echinococcus multilocularis. Numerous vesicles in tissue; H&E stain. Note there is no single limiting membrane, as occurs in E. granulosus hydatid cysts. This growth tends to mimic a metastatic cancer. doi:10.1128/9781555819002.ch34.f50

(Upper row) Coenurus (Taenia multiceps, T. serialis) removed from a subcutaneous nodule in the shoulder. (Left) Gross specimen. (Middle) Cross section. Although the species was not identified in this case, the pathology is consistent with T. serialis. (Right) Higher magnification (200×) of the same specimen shown on the left. The black arrow points to hooklets in one of the protoscolices. (Lower row) Coenurus from a human eye. (Left) Taenia species with multiple protoscolices (circle); no daughter cysts develop in a coenurus. (Middle) Higher magnification of one of the protoscolices; note the hooklets (circle). (Right) High magnification of the protoscolex showing multiple hooklets. (Courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch34.f51

Spirometra sparganum larva. (Top) Spargana are larval forms of various tapeworms in the genus Spirometra. Spargana are white and ribbonlike in shape, range from a few millimeters to >30 cm in length, and are actively motile. The solid sparganum lacks suckers and bladder walls; there are irregular bundles of muscle fibers, typical folded tegument, and calcareous corpuscles in the parenchyma (Armed Forces Institute of Pathology photograph). (Middle) Spirometra mansonoides sparganum; note the calcareous corpuscles, which are refractile sand-like particles in the parenchyma (circle) (courtesy of R. E. Pugh, http://parasite.org.au/pugh-collection/Spirometra%20mansonoides%204%2021.jpg_Index.html). (Bottom) Proliferating sparganum in groin tissue of a patient from Paraguay; H&E (courtesy of the CDC Public Health Image Library). doi:10.1128/9781555819002.ch34.f52

Diagram of the cross section of a trematode. Note the coiled uterus (UT) containing eggs, the lobed ovary (OV), intestinal ceca (IC), and excretory canals (EC). Also, note the large ventral sucker (VS). (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f53

(Left) Diagram of male and female Schistosoma trematodes. The female worm is lying with the male worm in copulo. Note the small tuberculations on the dorsal tegument of the male worm. (Right) Sections of adult Clonorchis sinensis in the common bile duct. Note that in different sections, different structures are visible, including the intestinal ceca, the ovary, and parts of the testis. Also note the marked proliferation of the bile duct epithelium. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f54

(Upper) Cross section of a Schistosoma mansoni adult worm pair in the mesenteric venule; note the smaller female worm is lying within the gynecophoral canal of the male worm (courtesy of the National Library of Medicine, National Institutes of Health). (Lower) Schistosoma adults in tissue. Note that the smaller female worm is lying within the gynecophoral canal of the male worm. The intestinal ceca are visible within both male and female worms. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f55

(Upper) Schistosoma haematobium eggs in bladder biopsy; note the large terminal spine (circle). (Lower, left) S. haematobium eggs in bladder biopsy, note the terminal spine (circle); (right) S. mansoni in liver tissue. (Courtesy of Munaf Desai, Al Qassini Hospital, Shatjah, United Arab Emirates, and the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch34.f56

(Upper) Schistosoma haematobium egg in urine; note the egg shell on the left and the hatched miracidium on the right (courtesy of Aaron Hill, Virginia Commonwealth University Medical Center). (Lower) Stained miracidium larva, hatched egg. Note the anterior end in both images. doi:10.1128/9781555819002.ch34.f57

(Upper) Two Paragonimus westermani parasites within a lung cavity. Note the dark, small spots of the vitellaria just within the tegument. The dark openings represent the ceca, with clear portions of the uterus. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) (Lower) Paragonimus sp. from lung biopsy; H&E. Eggs measured 80 to 90 μm by 40 to 45 μm, but were not identified to species. (Courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch34.f58

(Upper) Adult Fasciola hepatica embedded in the intestinal wall. The parasite presents as an oval to round mass limited by a spined cuticle (circle). The parasitic parenchyma is punctuated by multiple sections through the gut. The two centrally located tubular structures, separated by a light-staining muscular sucker (arrow), are part of the reproductive apparatus of the parasite. A marked inflammatory response is present in the adjacent host tissues, and fresh RBCs can be seen near the parasite. (Lower) Adult F. hepatica in the liver. Note that the intestinal ceca (arrow) and portions of the testes are clearly visible (T). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman; photograph courtesy of B. C. Walton.) doi:10.1128/9781555819002.ch34.f59

Clonorchis sinensis. (Upper) Cross sections of adult flukes within the bile duct, which shows marked hyperplasia of epithelium. (Lower) Adult fluke in bile duct, larger magnification. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f60

Echinostoma adult worm. (Upper) Stained adult worm characterized by having a circumoral disk with a crown of spines surrounding the small oral sucker (courtesy of www.k-state.edu). (Lower) Enlarged image of the crown of spines (surrounding the oral sucker). The living worm is reddish gray and measures 2.5 to 6.5 mm in length by 1 to 1.35 mm in width. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f61

Alaria americana mesocercaria in an autopsied human liver. (Upper) Note the evidence of both the oral sucker and the acetabulum (ventral sucker) (arrow). (Lower) A. americana. Note the oral and ventral suckers (higher magnification). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman. Photograph courtesy of R. S. Freeman.) doi:10.1128/9781555819002.ch34.f62

Malaria. Section through the cerebrum showing more congestion of the white matter (petechial hemorrhages) than of the gray (circle). (Armed Forces Institute of Pathology photograph.) doi:10.1128/9781555819002.ch34.f63

(Upper) Cerebral malaria showing cerebral capillaries congested with parasitized erythrocytes (arrow). Parasitized erythrocytes stick to the endothelium and occlude the capillaries. (Lower) Note the capillary containing parasitized erythrocytes; note the brownish malarial pigment (higher magnification). (Armed Forces Institute of Pathology photograph.) doi:10.1128/9781555819002.ch34.f64

Malarial pigment present in the spleen. The spleen is enlarged to about 500 g during an acute attack; it is soft, diffusely pigmented, and congested and has rounded edges. The phagocytic cells lining the splenic sinuses contain malarial pigment, free parasites, and parasitized erythrocytes. During an acute attack, malarial pigment is evenly distributed throughout the spleen. doi:10.1128/9781555819002.ch34.f65

Diagram of amastigotes. (Left) Leishmania donovani amastigotes in a spleen smear. Each amastigote contains the dark, round nucleus and the bar-shaped kinetoplast. When cells are packed with amastigotes, often the complete morphology for each amastigote is not visible. (Right) Trypanosoma cruzi amastigotes in cardiac muscle. Each amastigote contains the nucleus (round, dark) and the kinetoplast (small bar). (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch34.f66

Leishmania spp. (Upper) Smear of bone marrow showing many intracellular and extracellular Leishmania organisms. The amastigotes (Leishman-Donovan bodies) (circle) appear larger in smears than in tissue sections. The nucleus (longer dark object within the circle) and kinetoplast (smaller dark object within circle) are distinct in these organisms. (Lower) Single amastigote in the dermis (arrow) stained with Brown-Hopps tissue Gram stain. Note spherical nucleus and rod-shaped kinetoplast (Armed Forces Institute of Pathology photograph). doi:10.1128/9781555819002.ch34.f67

Leishmania donovani. (Left) Section of liver showing dilated sinusoids and greatly enlarged Kupffer cells (arrow); Brown-Hopps tissue Gram stain. (Right) Numerous black amastigotes in Kuppfer's cells; note kinetoplasts (arrows); Wilder's reticulum stain. (Armed Forces Institute of Pathology photographs.) doi:10.1128/9781555819002.ch34.f68

Trypanosoma cruzi. (Upper) Transillumination of apex highlights the apical aneurysm. (Lower) The thinned ventricular wall shows muscle fiber loss and fibrosis most prominent near the aneurysm. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f69

Trypanosoma cruzi. (Upper) Amastigotes in cardiac tissue. Note that many organisms are present; however, it is difficult to see differentiation between the nuclei and kinetoplasts. (Lower) Higher magnification of the amastigotes in cardiac muscle; note one of the kinetoplasts (looks like a small bar) (arrow). doi:10.1128/9781555819002.ch34.f70

Wuchereria bancrofti. (Upper) Multiple sections of the worm in a dilated lymphatic vessel. Note the thin, threadlike structures in utero (circle). Various lengths are seen, depending on the actual tissue cut. Although these helminths are nematodes, they are shown with the blood parasites, since blood is the primary specimen for diagnostic purposes. (Lower) At higher power, the developing microfilariae in utero (circle) and cuticle are seen. (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f71

Onchocerca sp. (Upper) Microfilaria of Onchocerca sp. (arrow) detected in biopsied skin in the interstitium of the dermis; H&E stain. (Lower) The gut is seen as a cross section in the lower portion of the image and longitudinally in the upper portion; note the curvy microfilariae in different lengths, depending on the direction of the cut (circle). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f72

Mansonella streptocerca in a section of skin. Note the long, slender microfilariae in utero (arrow). (From A Pictorial Presentation of Parasites: a cooperative collection prepared and/ or edited by H. Zaiman.) doi:10.1128/9781555819002.ch34.f73