Protozoan Quiz

Ameobas

Unicellular

Eukaryotic (more complex than bacteria)

Transmission: Ingestion of cysts from food and water contaminated with fecal material

Whats the troph parasite? (20 um)

Entamoeba histolytica (20 u)— Pathogenic

Whats the cyst? (10-20 um)

Entamoeba histolytica (20 u)— Pathogenic

Entamoeba histolytica

Cyst= 10-20 um

Troph= 15-20 um

• Type: Amoeba

• ID (lab clues): Troph — thin, delicate chromatin ring; central compact karyosome; ingested RBCs (key). Cyst — up to 4 nuclei, smooth-ended chromatoid bars. ~20 μm troph.

• Host/site/lifecycle: Humans; colon; fecal-oral cyst ingestion; asexual division; invasive potential (portal spread to liver).

• Symptoms / disease links:

  • Non-dysenteric GI illness (abdominal pain, nausea, flatulence, irregularity, fatigue).

  • Amoebic dysentery — bloody/mucous stools, flask-shaped ulcers, perforation risk, typically no fever.

  • Amoebic liver abscess (sterile core; amoebae at margins), lungs as secondary; amoeboma can mimic colon cancer.

• Co-infections: Bacterial GI pathogens can co-infect.

• Bloody stool? Yes.

Entamoeba dispar

Cyst= 10-20 um

Troph= 15-20 um

Commensal Amoeba

• ID: Morphologically identical to E. histolytica; no RBC ingestion.

• Pathogenic? No.

• How to differentiate: Rapid EIA specific for E. histolytica (or molecular).

• Bloody stool? No.

Entamoeba hartmanni

Troph=8-10 um

Cyst= 6-8 um

Commensal

• Type: Amoeba

• ID: “Small E. histolytica.” Troph ~8–10 μm, cyst ~6–8 μm.

• Bloody stool? No.

Entamoeba coli

Troph= 15-50 um

Cyst= 10-35 um

commensal

• Type: Amoeba

• ID: Largest intestinal amoeba. Troph 15–50 μm with eccentric karyosome, coarse/lumpy chromatin; Cyst 10–35 μm with ≥5 nuclei; splintered chromatoid bars.

• Bloody stool? No.

• Pitfall: Often mistaken for E. histolytica — count nuclei and check nuclear detail.

Entamoeba polecki

cyst= 9-25 um

troph=10-25 um

commensal

• Type: Amoeba (pigs/monkeys; under-diagnosed).

• ID: Mixed features between E. histolytica and E. coli; variable chromatoid bodies.

• Testing emphasis: You won’t be asked to visually ID on tests.

Endolimax nana

Troph= 6-12 um

Cyst= 5-10 um

commensal

• Type: Amoeba

• ID: Smallest intestinal amoeba. Troph 5–15 × 6–8 μm with big dense karyosome and thin membrane (“ball-and-socket”); cyst 6–8 μm, nuclei look like “potato with eyes.”

• Stains: Iron hematoxylin historically helpful to separate from Iodamoeba.

• Bloody stool? No.

Iodamoeba bütschlii

Troph= 8-20 um

Cyst= 5-20 um (usually 10-12 um)

commensal

• Type: Amoeba

• ID: Cyst with single nucleus and large karyosome, glycogen vacuole (iodine clears fast, so appears as a large clear vacuole); troph has large dense karyosome and “dirty” cytoplasm.

• Bloody stool? No.

Blastocystis (formerly B. hominis)

opportunistic; variable

• Type: Stramenopile (grouped here); many subtypes; fecal-oral.

• ID: Vacuolated form most common in stool: 5–40 μm with huge central vacuole (90 percent of cell) and 2–4 peripheral nuclei; cyst ~3–10 μm and hard to find.

• Symptoms: Often asymptomatic; when ill — nonspecific abdominal pain, bloating, acute/chronic diarrhea, gas; association with IBD noted. No fecal leukocytes.

• Co-infections: Very common.

• Stains/tests: Concentration + Trichrome

• Bloody stool? No.

Dientamoeba fragilis

Troph= 5-15 um

Cyst= 4-8 um

occasionally pathogenic

• Type: Flagellate (but no external flagella); worldwide.

• ID: 4–12(15) μm trophs; 1–2 nuclei (20–40 percent are uninucleate); fragmented karyosome (3–5 granules); no peripheral chromatin; “dirty” cytoplasm. Not seen on wet preps or in concentrates; cyst stage recently described.

• Symptoms: Colicky pain, fatigue, weight loss (variable).

• Bloody stool? No.

• Testing: Permanent stained smears; molecular if available.

Giardia lamblia / intestinalis / duodenalis

Troph= 10-20 um

Cyst= 11-14 um

pathogenic; common in US

• Type: Flagellate

• ID: Troph 10–20 μm with 2 nuclei, 2 parabasal bodies, 1 axostyle, 8 flagella; falling-leaf motility; cyst 11–14 μm with up to 4 nuclei (often pale on stains). Attaches to upper small intestine without invasion.

• Epi: Daycare, campers/untreated water, beavers/other reservoirs, MSM; incubation 12–20 days.

• Symptoms: Steatorrhea — greasy, foul, gray/green, explosive watery diarrhea, flatulence, cramps, distention/belching; chronic relapsing pattern possible.

• Bloody stool? No.

• Testing: FE concentration + Trichrome; collect ≥3 stools on non-consecutive days (intermittent shedding). Rapid EIA, string test

Trichomonas vaginalis

Troph= 7-25 um

pathogenic (urogenital)

• Type: Flagellate

• ID: Only troph stage, found in urine, vaginal/prostatic secretions; sexual transmission.

• Symptoms: Women — itching, burning, dysuria, foamy yellow-green discharge with odor. Men — often asymptomatic; may have prostatitis/urethritis.

• Testing: Direct wet prep for motile trophs; (molecular/antigen tests exist, but your deck emphasizes wet prep recognition).

Trichomonas hominis / tenax

Troph=6-20 um

nonpathogenic

• Type: Flagellates

• ID: T. hominis colon, T. tenax mouth; no cyst stage; look for motile trophs on wet prep; hard to see on permanents.

Chilomastix mesnili

Troph= 10-15 um

Cyst= 6-11 um

commensal

• Type: Flagellate

• ID: Troph 10–15 μm tear-drop with eccentric nucleus/karyosome and a visible cytostome (“mouth”); rotating/wobbling motility. Cyst lemon-shaped with anterior “nipple”; 6–11 μm.

• Bloody stool? No.

• Where: Cecum/colon.

Balantidium coli

Troph= 50-100 um

Cyst= 50-70 um

pathogenic

• Type: Ciliate (largest protozoan of humans)

• ID: Troph 50–100 μm with cilia, macronucleus (+ micronucleus), cytostome; cyst 50–70 μm with thick wall, macronucleus, +/- cytostome, no cilia.

• Host/site/lifecycle: Humans, close association with pigs; colon/cecum; ingest cysts from contaminated food/water.

• Symptoms: Asymptomatic to chronic non-bloody diarrhea; fulminant disease causes mucoid, bloody stools, weight loss, explosive diarrhea; flask-shaped lesions and perforation possible (hyaluronidase implicated).

• Bloody stool? Yes (in severe disease).

• Risk: Poor sanitation, alcoholism, malnourishment, immunocompromise.

Cystoisospora (Isospora) belli

Troph= 25-33 µm x 10-19 µm

Cyst= 20–33 and 8–19 um

pathogenic

• Type: Coccidia; small intestine.

• ID: Oocyst: immature with 1 sporoblast; mature with 2 sporocysts, each with 4 sporozoites.

• Symptoms: Severe diarrhea, steatorrhea, fever, nausea, weight loss; notorious in HIV-positive patients.

• Bloody stool? No.

• Stains/tests: Modified acid-fast; stool O&P.

Cryptosporidium parvum

Cyst= 4-6 um

Troph= 2-3 um

Cryptosporidium parvum — pathogenic

• Type: Coccidia (infects brush border of small intestinal epithelium).

• ID: Oocysts ~4–6 μm.

• Symptoms: Profuse watery diarrhea, cramps, nausea, anorexia — self-limited in immunocompetent; chronic/severe and extra-intestinal in immunocompromised.

• Bloody stool? No — typically watery.

• Stains/tests: Acid-fast; DFA; ImmunoCard STAT lateral-flow EIA; chromogenic immunoassay.

Cyclospora (cayetanensis)

Cyst= 8-10 um

Cyclospora (cayetanensis) — pathogenic

• Type: Coccidia; emerging; 8–10 μm.

• ID/testing: Requires specific O&P order for Cyclospora; 3 specimens optimal (intermittent shedding).

• Symptoms: Flu-like prodrome, explosive diarrhea, weight loss, nausea/vomiting; outbreaks linked to fresh produce.

• Bloody stool? No.

Sarcocystis

9–16 μm.

pathogenic (foodborne)

• Type: Coccidia; 9–16 μm.

• Hosts: Human = definitive host; pig = intermediate (also beef).

• Acquisition: Undercooked beef/pork.

• Clinical: Foodborne illness; not a common stool O&P target.

• Bloody stool? No.

Microsporidia

1.5 - 2 um

pathogenic in immunocompromised

• Type: Obligate intracellular; 1.5–2 μm, very small.

• Dx: “Impossible to find in feces” on routine O&P; biopsy is the best specimen per deck.

• Bloody stool? No.

Which ones cause bloody stool?

Do: E. histolytica (amoebic dysentery), Balantidium coli (fulminant disease)

E. histolytica (pathogenic) vs E. dispar/E. hartmanni/E. coli (non-pathogenic):

• RBCs inside troph → points to E. histolytica.

• Size (tiny = hartmanni), many cyst nuclei & coarse/eccentric nuclear detail = E. coli.

• Antigen EIA specific to E. histolytica or PCR to confirm.

Iron hematoxylin

Classic differentiation aid for small amoebas (Endolimax vs Iodamoeba) in older prep notes

Acid-fast/Modified acid-fast positive?

• Cryptosporidium — acid-fast (4–6 μm).

• Cystoisospora — modified acid-fast (oocysts with 1 sporoblast → 2 sporocysts with 4 sporozoites each).

• (Cyclospora in practice is also acid-fast positive, but your slides focus on ordering specific O&P with three specimens rather than showing the stain panel.)