Chapter 30 : Parasitic Infections in the Compromised Host

(Top) Entamoeba histolytica trophozoites containing ingested RBCs. (Middle) Entamoeba histolytica/E. dispar cysts. (Bottom) Amebic liver abscess in section; note the “flask-shaped” ulcer. doi:10.1128/9781555819002.ch30.f1

(Top) Naegleria fowleri trophozoite (note the large karyosome within the nucleus). (Row 2) N. fowleri trophozoites within brain tissue. (Row 3) N. fowleri trophozoites; note “globby/rounded” pseudopods. (Bottom, left) Flagellated form of Naegleria; (right) cyst of Naegleria, not seen in human tissue. (Bottom images courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch30.f2

(Top, left) Acanthamoeba trophozoite (note the sharp, spiky pseudopodia); (right) Acanthamoeba cyst (note the hexagonal double wall). (Row 2) Acanthamoeba keratitis. (Row 3) Cutaneous Acanthamoeba infection. (Bottom) Acanthamoeba cysts in brain: case of GAE. Note that cysts are present in tissue, unlike Naegleria infections, where only trophozoites are seen in tissue. (Lower three images courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch30.f3

Balamuthia mandrillaris. (Top) Trophozoites. (Middle) Cysts. (Bottom, left) Trophozoite in brain tissue; (right) cyst in brain tissue (courtesy of the CDC Public Health Image Library; lower right from the University of Kentucky Hospital, Lexington, KY). doi:10.1128/9781555819002.ch30.f4

Sappinia sp. (Top) Trophozoites viewed under differential interference contrast (DIC); note there are two nuclei. (Middle) Cysts viewed under DIC. (Bottom) Four trophozoites (yellow arrows) of S. pedata in brain tissue, H&E stain; in three of the amebae, two nuclei are visible (courtesy of the CDC Public Health Image Library). doi:10.1128/9781555819002.ch30.f5

Blastocystis sp. Central body forms, Wheatley's trichrome stain. doi:10.1128/9781555819002.ch30.f6

(Top, left) Giardia lamblia trophozoite (note two nuclei, curved median bodies, and linear axonemes); (right) G. lamblia cyst. (Middle) Multiple Giardia trophozoites seen in gastrointestinal tract; note the enlargement (courtesy of Medical Sciences, Indiana University, http://medsci.indiana.edu/c602web/602/c602web/nutrit/docs/cas4_giard.htm). (Bottom) G. lamblia cyst (large) and Cryptosporidium spp. oocysts (small) demonstrating fluorescence in the fecal FA immunoassay. Note in the left image that the background demonstrates use of the counterstain, while in the right image no counterstain was used. doi:10.1128/9781555819002.ch30.f7

Toxoplasma gondii. (Top) Tissue cyst containing 8 to 20 parasites. (Middle) Organisms in bone marrow. (Bottom, left) Tachyzoites in tissue culture; (right) granuloma in eye. doi:10.1128/9781555819002.ch30.f8

Cryptosporidium. (Top) Oocysts stained using the modified acid-fast stain; note the spherical shape. Oocysts measure 4 to 6 μm and some contain sporozoites that are visible. (Middle) Organisms visible along the brush border of intestinal mucosa. (Bottom) FA procedure showing fluorescent apple-green oocysts; counterstain present. doi:10.1128/9781555819002.ch30.f9

Cyclospora cayetanensis. (Top) Oocysts stained using the modified acid-fast stain (note the spherical shape; oocysts measure 8 to 10 μm; some oocysts do not stain, thus the organisms are said to be “modified acid-fast variable”). (Row 2) Autofluorescent oocysts using the appropriate filters for calcofluor white. (Row 3) Oocysts stained using the hot safranin method. (Bottom) Oocysts stained using the routine Wheatley's trichrome stain; note the oocysts do not stain well, but appear to be “ghost” cells. doi:10.1128/9781555819002.ch30.f10

Cystoisospora (Isospora) belli. (Top) Wet mounts; immature oocyst (contains single sporoblast) on the left and mature oocyst on the right. (Row 2) Immature oocysts containing a single sporoblast, modified acid-fast stain. (Row 3) Mature oocysts containing two sporoblasts, modified acid-fast stain. (Bottom) Immature (one sporoblast) and mature (two sporoblast) oocysts in unstained wet mount viewed using UV fluorescence microscopy. (Bottom images courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch30.f11

Cystoisospora (Isospora) belli. (Upper) Oocyst containing two sporocysts, each containing four sporozoites. (Lower) Developing stages in tissue, stained with hematoxylin and eosin (courtesy of the CDC Public Health Image Library). doi:10.1128/9781555819002.ch30.f12

Sarcocystis sp. (Upper, left) Sporulated oocyst in unstained wet mount; (right) sporulated oocyst in a wet mount viewed under UV microscopy. (Lower, left) Sporocyst released from the oocyst; (right) sporocyst released from the oocyst, wet mount viewed under DIC microscopy. (Courtesy of the CDC Public Health Image Library.) doi:10.1128/9781555819002.ch30.f13

Sarcocystis sp. in human muscle tissue (note the bradyzoites contained within the sarcocyst, visible in the lower image). doi:10.1128/9781555819002.ch30.f14

Microsporidia. Microsporidial spores seen in nasopharyngeal aspirate from AIDS patient; note the horizontal or diagonal lines (arrows) representing the polar tubules within the spores, stained with Ryan modified trichrome stain. doi:10.1128/9781555819002.ch30.f15

Microsporidial spores. (Upper) Encephalitozoon intestinalis stained with calcofluor white. (Lower) Monoclonal-antibody-based immunofluorescence identification of Encephalitozoon hellem (Courtesy of the CDC Public Health Image Library). doi:10.1128/9781555819002.ch30.f16

Leishmania donovani in bone marrow; specimen stained using Giemsa stain. Note the individual amastigotes with the larger nucleus and bar-shaped kinetoplast (circles). doi:10.1128/9781555819002.ch30.f17

Strongyloides stercoralis. (Top) Rhabditiform larvae seen in bronchoalveolar lavage fluid specimen, Giemsa stain (larvae can also be seen in sputum in heavy infections or in the hyperinfection syndrome). (Middle) Larva from sputum, Gram stain. (Bottom) Tracheal aspirate containing many larvae (courtesy of Marc Roger Couturier, ARUP Laboratories, Department of Pathology, University of Utah). doi:10.1128/9781555819002.ch30.f18

Morphology of malaria parasites. Column 1 (reading down), Plasmodium vivax (note enlarged infected RBCs): ( 1 ) early trophozoite (ring form) (note one RBC contains two rings—not that uncommon); ( 2 ) older ring, note ameboid nature of rings; ( 3 ) late trophozoite with Schüffner's dots (note enlarged RBC); ( 4 ) developing schizont; ( 5 ) mature schizont with 18 merozoites and clumped pigment; ( 6 ) microgametocyte with dispersed chromatin. Column 2, Plasmodium ovale (note enlarged infected RBCs): ( 7 ) early trophozoite (ring form) with Schüffner's dots (RBC has fimbriated edges); ( 8 ) early trophozoite (note enlarged RBC, Schüffner's dots, and RBC oval in shape); ( 9 ) late trophozoite in RBC with fimbriated edges; ( 10 ) developing schizont with irregular-shaped RBC; ( 11 ) mature schizont with eight merozoites arranged irregularly; ( 12 ) microgametocyte with dispersed chromatin. Column 3, Plasmodium malariae (note normal or smaller than normal infected RBCs): ( 13 ) early trophozoite (ring form); ( 14 ) early trophozoite with thick cytoplasm; ( 15 ) late trophozoite (band form); ( 16 ) developing schizont; ( 17 ) mature schizont with nine merozoites arranged in a rosette; ( 18 ) macrogametocyte with compact chromatin. Column 4, Plasmodium falciparum: ( 19 ) early trophozoites (the rings are in the headphone configuration with double chromatin dots); ( 20 ) early trophozoite (accolé or appliqué form); ( 21 ) early trophozoites (note the multiple rings per cell); ( 22 ) late trophozoite with larger ring (accolé or appliqué form); ( 23 ) crescent-shaped gametocyte; ( 24 ) crescent-shaped gametocyte. Column 5, Plasmodium knowlesi (with the exception of image 29, these were photographed at a higher magnification; note normal or smaller than normal infected RBCs; courtesy of the CDC Public Health Image Library): ( 25 ) early trophozoite (ring form); ( 26 ) early trophozoite with slim band form; ( 27 ) late trophozoite (band form); ( 28 ) developing schizont; ( 29 ) mature schizont with merozoites arranged in a rosette; ( 30 ) microgametocyte with dispersed chromatin. Note: Without the appliqué form, Schüffner's dots, multiple rings per cell, and other developing stages, differentiation among the species can be very difficult. It is obvious that the early rings of all four species can mimic one another very easily. Remember: One set of negative blood films cannot rule out a malaria infection. (Figure courtesy of Garcia LS, Clin Lab Med 30:93–128, 2010.) doi:10.1128/9781555819002.ch30.f19

Three examples of blood films containing the ringlike forms of Babesia spp. Various ring forms, multiple rings per cell; some rings present outside of the red blood cells (circle); note the typical image of the “Maltese cross” configuration of the four rings (square). Note: it is rare to see Plasmodium rings outside of the RBC. doi:10.1128/9781555819002.ch30.f20

(Upper) Trypanosoma cruzi trypomastigotes in a peripheral blood smear; note the large kinetoplast (arrow). (Lower) Amastigote in cardiac muscle; note the actual amastigote with nucleus and kinetoplast (arrow). doi:10.1128/9781555819002.ch30.f21

Sarcoptes scabiei “itch mite.” (Upper) Mite from skin scraping preparation (note the four pairs of legs). (Lower) Hands of a homeless individual with AIDS and severe scabies (crusted scabies) (courtesy of the Wikimedia Commons, Adam Cuerden; released into the public domain by author). doi:10.1128/9781555819002.ch30.f22