Parasitology Practical Prep

Name this intestinal amoeba

Entamoeba histolytica

12–15 µm

1–4 nuclei, central karyosome, even chromatin, and cigar-shaped chromatoid bodies with blunt/rounded ends

Troph ingests RBCs

stool O&P

dysentery, extraintestinal amebic liver abscesses

Name this intestinal amoeba

Entamoeba dispar

>10 µm

1–4 nuclei, rounded chromatoid bars

NEVER ingests RBCs

Reported as "Entamoeba histolytica/dispar" unless separated by PCR/antigen testing

Non-pathogenic commensal

Name this intestinal amoeba

Entamoeba hartmanni

5–10 µm

1–4 nuclei and rounded chromatoid bodies

Non-pathogenic commensal

Name this intestinal amoeba

Entamoeba coli

10–35 µm

1–8 nuclei (mature = 8), eccentric karyosome, coarse/uneven peripheral chromatin, and splintered/sharp/pointed chromatoid bodies

Non-pathogenic commensal

Troph = "junky cytoplasm"

Name this intestinal amoeba

Endolimax nana

5–10 µm

oval cysts with up to 4 blot-like/clumped nuclei and NO peripheral chromatin

Non-pathogenic commensal

Name this intestinal amoeba

Iodamoeba bütschlii

5–20 µm

1 nucleus with a large karyosome and a prominent, large glycogen vacuole that stains dark brown with iodine

Non-pathogenic commensal

Name this intestinal amoeba

Blastocystis hominis

Spherical cell (5–30 µm, avg 8–10 µm) with a large central vacuole/body compressing 1–4 dark nuclei into a thin outer rim of cytoplasm

Diarrhea/abdominal discomfort

Name this flagellate

Giardia duodenalis

9–12 µm

Oval with 4 nuclei and visible internal fibrils/axonemes

Trophozoite (10–20 µm × 12–15 µm): Pear/pyriform shape with 2 nuclei ("monkey face")

"Beaver Fever" diarrhea

Case clues: outbreaks from drinking untreated water or daycare contact

Name this flagellate

Dientamoeba fragilis

Flagellate with NO CYST STAGE

9–12 µm

contain 1 or 2 nuclei (60–70% are binucleate) with karyosomes fragmented into 4–8 granules; no peripheral chromatin

diarrhea, abdominal pain

Case Clues & Sample: Transmitted via helminth eggs (Ascaris / Enterobius), PVA-fixed trichrome stain

Name this flagellate

Chilomastix mesnili

Cyst (6–10 µm)

lemon-shaped with a clear knob at one end

Trophozoite (10–15 µm) is pear-shaped with a curved cytostomal fibril ("shepherd's crook")

Non-pathogenic commensal

Name this ciliate

Balantidium coli

Cyst (50–70 µm) is round with a thick wall and visible macronucleus

Trophozoite (50–100 µm) is ciliated with a kidney bean-shaped macronucleus

Case Clues & Sample: Exposure to swine/pigs

Specimen: Stool wet mount/O&P

dysentery, intestinal ulceration

Name this coccidia

Cryptosporidium

Small, spherical oocysts (4–6 µm)

Modified Acid-Fast positive (stains bright pink/red)

Autoinfective and chlorine-resistant

Case Clues & Sample: Daycare outbreaks, contaminated swimming pools/water supplies

diarrhea; life-threatening in AIDS/immunocompromised patients

Name this coccidia

Cyclospora cayetanensis

Spherical oocysts (8–10 µm — twice the size of Cryptosporidium)

Modified Acid-Fast positive (variable/ghost staining)

Autofluoresces intense blue under UV light

Case Clues & Sample: Summer outbreaks associated with imported fresh produce

relapsing watery diarrhea

Name this coccidia

Cystoisospora belli

Large, ellipsoidal/spindle-shaped oocysts (25–30 µm × 10–19 µm) containing 1–2 sporoblasts

Modified Acid-Fast positive and autofluoresces blue under UV light

Severe watery diarrhea in AIDS patients

Name this free-living amebae

Naegleria fowleri

Amoeboid trophozoites with blunt pseudopods in CSF wet mount

Case Clues & Sample: Water-skiing or swimming in warm fresh water; nasal entry through cribriform plate

Primary Amoebic Meningoencephalitis (PAM) — rapidly fatal CNS infection

Name this free living amebae cyst form

Acanthamoeba

double-walled wrinkled/star-shaped cysts

Case Clues & Sample: Contact lens wearers using homemade saline or tap water

Specimen: Corneal scrapings, tissue biopsy, CSF

Granulomatous Amoebic Encephalitis (GAE); Acanthamoeba keratitis

Name this flagellate troph

Trichomonas vaginalis

Pear-shaped trophozoite (7–23 µm) with 4 anterior flagella, axostyle, short undulating membrane, and jerky motility

NO CYST STAGE

Case Clues & Sample: Sexually transmitted, Vaginal swab wet mount, urine sediment wet mount during routine urinalysis

Name this hemoflagellate

Leishmania spp.

Diagnostic human stage = amastigote (intracellular in macrophages, 2–4 µm, featuring a nucleus and a rod-like kinetoplast) Vector stage = promastigote

Case Clues & Vector: Vector = Phlebotomine Sandfly

Specimen: Tissue biopsy, bone marrow

Skin ulcers, nasal septa destruction, donovani kala azar severe anemia

Name this hemoflagellate

Trypanosoma brucei

14–33 µm, with a small terminal kinetoplast, undulating membrane, and free flagellum

Case Clues & Vector: Vector = Tsetse fly

Specimen: Giemsa-stained blood smear, lymph node aspirate, CSF

African Sleeping Sickness

Name this flagellate

Trypanosoma cruzi

rigid 'C' or 'U' shape on blood smear with a very large terminal kinetoplast

Chagas Disease

Vector = Triatomine / Reduviid bug ("Kissing bug")

Name this plasmodium

Plasmodium falciparum

Infected RBCs are NORMAL size

Rings are small/delicate with double chromatin dots ("headphones"), appliqué/accolé forms, and multiple rings per RBC

Banana- or crescent-shaped gametocytes

Vector = female Anopheles mosquito

Most severe/deadly malaria

Name this plasmodium

Plasmodium vivax

Infected RBCs are ENLARGED

Trophozoite is amoeboid; Schüffner's dots present in RBC

Schizont contains >12 merozoites (12–24)

most widespread geographically (80% of cases)

Relapses due to hypnozoites in liver

Name this plasmodium

Plasmodium ovale

Infected RBCs are ENLARGED

OVAL-shaped with fimbriated/fringed/jagged edges and Schüffner's dots

Schizont contains 6–14 (avg 8) merozoites

liver hypnozoites cause malaria relapses

Name this plasmodium

Plasmodium malariae

Infected RBCs are NORMAL or SMALL size

Trophozoite forms a distinct band or basket form across the RBC

Schizont forms a symmetrical "rosette" pattern (6–12 merozoites surrounding central dark pigment)

Quartan malaria (72h cycle periodicity)

Name this plasmodium

Babesia microti

Small pleomorphic rings in normal RBCs

Classic hallmark: Maltese Cross (tetrad form of 4 merozoites)

NO MALARIAL PIGMENT (hemozoin) or gametocytes

Case Clues & Vector: Vector = Ixodes scapularis tick

fever, chills, hemolytic anemia

Name this nematode (roundworm)

Enterobius vermicularis (Pinworm)

Egg (50–60 × 20–30 µm) is D-shaped (flattened on one side) with a thick, smooth double-layered shell and larva inside

Adult female worm (8–13 mm) has a pointed tail

Case Clues & Sample: Gravid female migrates to perianal skin at night to lay eggs

Specimen: Cellophane Tape / Swube tube prep

intense perianal itching

Name this nematode (roundworm)

Trichuris trichiura (Whipworm)

Egg (50–55 × 20–25 µm) is barrel- or lemon-shaped, yellow-brown/bile-stained, with a thick shell and prominent clear mucoid plugs at BOTH poles (bipolar plugs)

Adult worm has a thin whip-like anterior end

Case Clues & Sample: Ingestion of eggs from soil/food

bloody diarrhea, rectal prolapse in children

Name this nematode (roundworm)

Ascaris lumbricoides (Large Roundworm)

Fertile egg (45–75 × 35–50 µm) is golden-brown with a thick, bumpy/mammillated (albuminous) outer shell

Unfertilized egg is larger, elongated, with irregular mammillations

Adult worm is large (6–12 inches / 15–35 cm)

Case Clues & Sample: Ingestion of embryonated eggs from soil/food

most common helminth infection worldwide

Larval migration through lungs causes pneumonia

adult worms cause bowel/biliary obstruction