Parasites

Entamoeba histolytica. (A) Resected segment of colon showing multiple ulcers with focal perforation due to amebiasis. (B) Amebic liver abscess with vial of aspirated abscess material demonstrating the characteristic “anchovy paste” appearance (Gross photos courtesy of Dr. Mae Melvin and Dr. E. West, CDC Public Health Image Library). (C) E. histolytica/E. dispar trophozoite (left) and cyst (right) (modified trichrome, 1000×). Reproduced with permission from Pritt BS. Parasitology Benchtop Reference Guide. Northfield, IL: College of American Pathologists, 2014. If ingested RBCs are seen within the cytoplasm of the trophozoite, then a presumptive diagnosis of E. histolytica can be made. Otherwise, the trophozoites and cysts of E. histolytica and E. dispar are indistinguishable. Note that two of the four nuclei are visible within the cyst as well as a prominent chromatoid body.

Giardia duodenalis trophozoites containing two nuclei, central axonemes and curved median bodies (left) and cyst with two of four nuclei visible (right) (trichrome stain, 1000×). Reproduced with permission from Pritt BS. Parasitology Benchtop Reference Guide. Northfield, IL: College of American Pathologists, 2014.

Round oocysts of Cryptosporidium sp. stained with a modified acid-fast stain. Note that not all oocysts stain equally and that sporozoites can occasionally be seen within some oocysts (1000×).

Round oocysts of Cyclospora cayetanensis stained using a modified acid-fast stain (1000×). They have a similar appearance to the oocysts of Cryptosporidium but are larger (8 to 10 µm in diameter). Note that not all oocysts stain uniformly, producing unstained “ghost” cells.

Immature oocyst of Cystoisospora belli containing one sporocyst (modified acid-fast, 1000×). The oocysts are significantly larger than those of Cryptosporidium spp. and Cyclospora cayetanensis, measuring approximately 33 µm in length.

Microsporidial spores of Enterocytozoon bieneusi in a concentrated fecal specimen demonstrating a characteristic band-like stripe (trichrome blue stain, 1000×). These tiny spores measure 0.8 to 1.4 µm in length and are therefore challenging to identify on standard microscopic preparations.

Acanthamoeba spp. trophozoites and cysts in a skin biopsy of an ulcerating skin lesion. Organisms are seen invading blood vessels in the dermis (left, H&E, 200×; arrow shows lumen of blood vessel). Higher magnification shows trophozoites with a small nucleus and large karyosome (top right) and cysts with a characteristic hexagonal double cell wall (bottom right) (H&E, 1000×).

Brain biopsy with multiple invading Balamuthia mandrillaris trophozoites; cysts are also commonly seen with both Balamuthia and Acanthamoeba infections but are not seen in this image.

Toxoplasma gondii. Free and intracellular arc-shaped tachyzoites in a brain impression smear (Giemsa, 1000×).

(A) Characteristic ulcer of cutaneous leishmaniasis with proximal lymphatic spread (courtesy of Dr. Martins Castro and Dr. Lucille K. Georg, CDC PHIL). (B) Air-dried impression smear from the edge of a cutaneous ulcer shows a macrophage containing numerous amastigotes (arrowhead denotes the macrophage nucleus, Giemsa, 1000×). A nucleus and rod-like kinetoplast can be seen within individual amastigotes (arrows).

(A) Trypanosoma cruzi trypomastigotes in a Giemsa-stained peripheral blood film. Note the characteristic large kinetoplast at the posterior end, central nucleus, and free flagellum at the anterior end (top, 1000×).

(B) T. cruzi amastigotes in cardiac tissue (H&E, 400×, inset 1000×).

Plasmodium vivax life cycle stages in the human host: early stage trophozoite (top left), late-stage trophozoite (top right), mature schizont (bottom left) and gametocyte (bottom right); (Giemsa, 1000×). Images from reference 312 .

Multiple parasite forms of Babesia MO1, showing pleomorphic intracellular forms, a characteristic “tetrad” form (arrowhead) and extracellular parasites (arrow) (Giemsa, 1000×). Image from reference 312 .

Strongyloides stercoralis larvae invading the intestinal mucosa in a case of hyperinfection (H&E, 1000×).

Sarcoptes scabiei mature mite (left), immature mite (bottom right) and egg (top right) in an unstained preparation of skin scrapings.