Parasitology - Protozoan (Doc Esme PPT)

Entamoeba histolytica

Only intestinal ameba that commonly causes amebic colitis and amebic liver abscess (ALA).

Entamoeba histolytica — Morphology

Morphologically identical to E. dispar and E. moshkovskii.

Entamoeba histolytica — Differentiation

PCR, Isoenzyme analysis, Monoclonal antibodies.

Entamoeba histolytica — Life cycle stages

Cyst (infective stage) and trophozoite (invasive stage).

Entamoeba histolytica

Humans are the primary host and reservoir.

Entamoeba histolytica — Mode of infection

Infection occurs through ingestion of mature quadrinucleate cysts.

Entamoeba histolytica — Encystation

Purpose: Protection and survival.

Trigger: Unfavorable conditions (stress).

Stage change: Trophozoite → Cyst.

Metabolism: Decreases (enters dormancy).

Structural change: Formation of a thick, protective wall.

Entamoeba histolytica — Excystation

Purpose: Multiplication and colonization.

Trigger: Favorable conditions (nutrients, moisture).

Stage change: Cyst → Trophozoite.

Metabolism: Increases (resumes normal activity).

Structural change: Rupture or dissolution of the cyst wall.

Entamoeba histolytica trophozoite

Motile; possesses pseudopodia; invasive stage; may contain ingested RBCs (diagnostic); size: 12–60 μm (average 20 μm).

Entamoeba histolytica cyst

Infective stage; spherical; size: 10–20 μm; contains 1–4 nuclei (mature cyst contains 4 nuclei); chromatoidal bars present; resistant to environmental conditions.

Entamoeba histolytica — Life cycle

1. Mature cysts passed in feces → 2. Contamination of food and water → 3. Human ingests mature cyst → 4. Excystation occurs in intestine → 5. Eight trophozoites released → 6. Trophozoites multiply by binary fission → 7. Some invade intestinal wall → 8. Others encyst and are passed in stool.

Entamoeba histolytica — Pathogenesis

Adheres to colonic mucosa via Gal/GalNAc lectin.

Causes cell destruction.

Causes apoptosis of intestinal cells.

Causes tissue invasion.

Entamoeba histolytica — Virulence mechanisms

Cytotoxic enzymes.

Contact-dependent killing.

Cytophagocytosis.

Entamoeba histolytica — Asymptomatic infection

Most common presentation.

Patients pass cysts in stool.

Entamoeba histolytica — Flask-shaped ulcer

Small defect in the mucosa and the large area of necrosis in the submucosa and muscularis layers covered by normal epithelium.

Entamoeba histolytica — Flask-shaped ulcer most common sites

Cecum.

Sigmoid colon.

Ascending colon.

Entamoeba histolytica — Ameboma

Rare (<1%); mass-like lesion in colon; may mimic carcinoma.

Entamoeba histolytica — Amebic liver abscess (ALA)

Most common extraintestinal disease.

Entamoeba histolytica — Amebic liver abscess symptom

Fever.

Right upper quadrant pain.

Tender hepatomegaly.

Entamoeba histolytica — Amebic liver abscess

Only 30% have diarrhea.

Entamoeba histolytica — Intestinal complication

Colonic perforation.

Entamoeba histolytica — Colonic perforation

Secondary bacterial peritonitis.

Entamoeba histolytica — Intestinal complication

Toxic megacolon.

Entamoeba histolytica — Extraintestinal complication

Rupture into pericardium (highest mortality).

Rupture into pleura.

Rupture into peritoneum.

Secondary amebic meningoencephalitis.

Bacillary dysentery (Shigella spp.)

Onset: Acute.

Fever: High.

Prodromal fever and malaise: Common.

Vomiting: Common.

Pallor and prostration.

Bacillary dysentery (Shigella spp.)

Watery bloody diarrhea.

Odorless stool.

Stool: Numerous PMNs, few RBCs.

Abdominal cramps: Common and severe.

Tenesmus.

Major illness generally resolves in a few days; weeks or more, no relapse.

Amebic dysentery

Onset: Gradual.

Fever: Uncommon.

Prodromal features: None.

Vomiting: None.

Patient usually ambulant.

Amebic dysentery

Fecal odor.

Bloody stool.

Stool: Moderate to few fecal PMNs, few RBCs, numerous E. histolytica cysts and trophozoites.

Abdominal cramps: Mild.

Tenesmus: Uncommon.

Major illness; relapse common; symptoms continue after remission; medical treatment for years.

Entamoeba histolytica — Amebic colitis differential diagnosis

Inflammatory bowel disease.

Entamoeba histolytica — Amebic liver abscess differential diagnosis

Pyogenic liver abscess.

Tuberculosis of the liver.

Hepatic carcinoma.

Entamoeba histolytica — Stool examination

Gold standard for intestinal infection.

Examine at least 3 stool specimens.

Entamoeba histolytica stool findings

Motile trophozoites.

Cysts.

RBC-ingesting trophozoites (diagnostic).

Charcot-Leyden crystals.

Entamoeba histolytica — Concentration techniques

FECT.

MIFC.

Entamoeba histolytica — Special tests

ELISA.

PCR.

Isoenzyme analysis.

Entamoeba histolytica — Amebic liver abscess serology

IHAT.

ELISA.

IFAT.

Entamoeba histolytica — Amebic liver abscess imaging

Ultrasound.

CT Scan.

MRI.

Entamoeba histolytica — Invasive amebiasis treatment

Metronidazole (drug of choice).

Entamoeba histolytica — Alternative treatment

Tinidazole.

Secnidazole.

Entamoeba histolytica — Asymptomatic cyst passers

Diloxanide furoate.

Entamoeba histolytica — Liver abscess treatment

Metronidazole.

Entamoeba histolytica — Liver abscess drainage

No response to therapy.

Large abscess.

Risk of rupture.

Entamoeba histolytica — Epidemiology

Approximately 50 million cases annually.

Causes 40,000–100,000 deaths/year.

Third most important parasitic disease worldwide.

Entamoeba histolytica — Endemic regions

South & Central America.

Africa.

Indian subcontinent.

East Asia.

Entamoeba histolytica — Higher-risk groups

Travelers.

Immigrants.

Institutionalized individuals.

HIV patients.

Men who have sex with men.

Entamoeba histolytica — Prevention and control

Improve sanitation and hygiene.

Safe disposal of human feces.

Safe drinking water.

Thorough washing of fruits and vegetables.

Handwashing.

Screen and treat food handlers and cyst carriers.

Health education programs.

Entamoeba histolytica — Infective stage

Mature quadrinucleate cyst.

Entamoeba histolytica — Diagnostic stage

Cyst and trophozoite.

Entamoeba histolytica — Pathognomonic finding

Trophozoite with ingested RBCs.

Entamoeba histolytica — Drug of choice

Metronidazole.

Entamoeba histolytica — Most common extraintestinal disease

Amebic liver abscess (ALA).

Entamoeba histolytica — Main transmission

Fecal-oral route.

Commensal amebae (Non-pathogenic intestinal amebae)

Non-pathogenic intestinal protozoa that do not cause disease.

Commensal amebae — Importance

May be mistaken for Entamoeba histolytica.

Health education programs.

Accurate identification prevents unnecessary treatment.

Commensal amebae — Genus Entamoeba

Entamoeba dispar, Entamoeba moshkovskii, Entamoeba hartmanni, Entamoeba coli, and Entamoeba polecki.

Commensal amebae — Other genera

Endolimax nana, Iodamoeba bütschlii, and Entamoeba gingivalis (oral cavity).

Commensal amebae — General life cycle

Cyst (infective stage) → Excystation in small intestine → Metacystic trophozoite → Trophozoite colonizes large intestine → Binary fission → Encystation in colon → Cysts passed in feces.

Commensal amebae — Transmission

Fecal-oral route through contaminated food and water.

Commensal amebae — Infective stage

Mature cyst.

Commensal amebae — Diagnostic stage

Cysts and trophozoites in stool.

Commensal amebae — Life cycle summary

Cyst in feces → Contaminated food/water → Ingestion of cyst → Excystation in small intestine → Metacystic trophozoites → Colonization of large intestine → Binary fission → Encystation → Cysts passed in stool.

Commensal amebae

Remain in the mucosal surface and do not invade tissues.

Entamoeba dispar

Morphologically identical to Entamoeba histolytica.

Non-pathogenic.

Entamoeba dispar — Differentiation

Differentiated by PCR and molecular methods.

Entamoeba moshkovskii

Non-pathogenic.

Morphologically identical to Entamoeba histolytica.

Entamoeba moshkovskii

Osmotolerant.

Survives 0–41°C.

Found worldwide.

Entamoeba hartmanni

"Small race" of Entamoeba histolytica.

Cosmopolitan distribution.

3–12 μm; more sluggish in movement.

Entamoeba hartmanni cyst

4–10 μm; mature cyst has 4 nuclei.

Entamoeba hartmanni

Does not ingest red blood cells.

Non-pathogenic.

Entamoeba coli

Most common intestinal ameba.

Entamoeba coli trophozoite

15–50 μm; sluggish movement; contains bacteria and debris.

Entamoeba coli cyst

10–35 μm; up to 8 nuclei; splinter-like chromatoidal bodies.

Endolimax nana

Common commensal ameba.

Endolimax nana trophozoite

5–12 μm; sluggish movement; large irregular karyosome.

Endolimax nana cyst

Mature cyst contains 4 nuclei.

Endolimax nana

Non-pathogenic.

Iodamoeba bütschlii trophozoite

4–20 μm; large vesicular nucleus.

Iodamoeba bütschlii cyst

Uninucleated; large glycogen vacuole; stains brown with iodine.

Iodamoeba bütschlii

Found worldwide and has a higher prevalence in tropical regions than in temperate regions.

Iodamoeba bütschlii cyst nucleus

Basket of flowers in shape.

Iodamoeba bütschlii nucleus

Does not undergo typical division.

Iodamoeba

Iodamoeba was coined to describe an ameba that stains well with iodine.

Iodamoeba bütschlii

Source of infection: contaminated hog feces.

Entamoeba gingivalis

Found in oral cavity.

No cyst stage.

Entamoeba gingivalis — Transmission

Kissing.

Droplet spray.

Shared utensils.

Entamoeba gingivalis

Common in periodontal disease.

Feeds on leukocytes and bacteria.

Commensal amebae — Diagnosis

Diagnosis.

Commensal amebae — Treatment

No treatment required.

Organisms are non-pathogenic.

Identification is important to avoid unnecessary anti-amebic therapy.

Commensal amebae — Epidemiology (Philippines)

Entamoeba coli ≈ 21%.

Endolimax nana ≈ 9%.

Iodamoeba bütschlii ≈ 1%.

Commensal amebae — Epidemiologic significance

Indicator of poor sanitation.

Reflects fecal contamination.

Commensal amebae — Prevention and control

Proper disposal of human waste.

Safe food and water.

Handwashing.

Personal hygiene.

Health education.

Commensal amebae — Key point

Non-pathogenic.

Commensal amebae — Transmission

Fecal-oral contamination.

Commensal amebae — Life cycle

Cyst → Trophozoite → Encystation → Cyst.

Commensal amebae

Important markers of sanitation and hygiene.

Must be differentiated from Entamoeba histolytica.

No treatment is necessary for asymptomatic infections.

Acanthamoeba spp.

Ubiquitous free-living ameba.

Acanthamoeba spp. — Habitat

Freshwater and seawater, soil, sewage, hospital equipment, contact lenses, and contact lens solutions.

Acanthamoeba spp. — Diseases caused

Acanthamoeba Keratitis (AK) and Granulomatous Amebic Encephalitis (GAE).

Acanthamoeba spp. trophozoite

Active feeding stage; infective stage; reproduces by binary fission; possesses characteristic acanthopodia ("thorn-like" projections); single nucleus with central nucleolus.

Acanthamoeba spp. cyst

Resistant and dormant stage; survives harsh environmental conditions; highly resilient.

Acanthamoeba spp. — Morphology

Two stages only: trophozoite and cyst.