PARASITOLOGY

Batch 2025 LECTURE/ DR. JING BAUTISTA

[TRANS] INTENSTINAL AMOEBA PAR1

Topic Outline GENUS ENTAMOEBA
• Intestinal Amoebae • Vesicular nucleus
o Genus Entamoeba • Small central karyosome
• Peripheral chromatin granules attached to the distinct nuclear
o Genus Endolimax
membrane
o Genus Iodamoeba • Entamoeba histolytica complex:
• Entamoeba Histolytica o E. histolytica
o E. dispar
o Diagnostic Characteristic
o E. moshkovskii
o Pathogenesis
o Diagnosis
o Epidemiology
o Treatment
o Prevention

INTESTINAL AMOEBAE
• 7 species of amoebae occur in human
• the only pathogenic is Entamoeba histolytica
• the rest are commensals – which do not cause disease in
human
o E. dispar
o E. moshkovski
o E. hartmanni
o E. coli GENUS ENDOLIMAX
o Endolimax nana • Vesicular nucleus
o Iodamoeba butschlii
• Relatively large
o Entamoeba polecki
• Irregular shaped ‘blot like’ karyosome anchored to the nucleus
§ An intestinal ameba of pigs and monkeys
by achromatic fibrils
§ Occasionally detected in humans, and is a
• No peripheral chromatin
probable cause of diarrhea
• Mainly differentiated according to structure and size
o Trophozoite – divide by binary fission
o Cyst-forming amoebae – go through nuclear division
§ Then, divided again after excystation in a
new host
THROPHOZOITES CYST

GENUS IODAMOEBA
• Large chromatin rich karyosome surrounded by a layer of
achromatic globules
• Anchored to the nuclear membrane by achromatic fibrils

• Vegetative or feeding • Infective form

stage • Resist to environment
• Metabolically active or change
motile • Non motile
• Seen in freshly passed • Inactive
wet stool • Seen in hard stool
• Multiply via binary fission
• causes damage to tissue

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SUMMARY! o Ectoplasm • Absence of ingested
(glasslike) – material
hyaline, outer • Lacks cyst wall
layer body
o Endoplasm – CYST
granular • Spherical; “ring and dot
• Progressively, directional appearance)
mobility • Size vary from 10-20
• Phagocytic stomata um
• (+) ingested RBC • (+) hyaline cyst wall –
ENTAMOEBA HISTOLYTICA o Pale, greenish, refractile if unstained
refractile bodies • Stained: appear thicker
• Pseudopod forming
in the cytoplasm and less uniform in size
• Non-flagellated protozoan parasite
• Never found within o May form
• 2 stage life cycle:
invades tissue plaques
o Invasive trophozoite
• Multiply by binary fission o Mass in
o Infective cyst
crescent
§ Quadrinucelated
fashion on one
§ Resistant to gastric acid and desiccation
side
§ Can survive in a moist environment for
• 1-4 nuclei – often not
several weeks
visible, unstained
• most invasive among the entamoeba parasites
• Karyosome may appear
eccentric
• Chromatoidal bars –
rod or cigar shaped
• Able to colonize or
invade the large bowel

• E. histolytica – stained by hematoxylin, trichrome

o Visualizes and identify nuclear structures
• Mode of Transmission : ingestion of cyst from fecally o Hematoxylin:
contaminated material § Ingested RBC – bluish black
o Others: § Cytoplasm – gray
o Venereal transmission via fecal oral contact § Nuclear structures – bluish black
o Direct colonic inoculation o Trichrome:
• Excystation: occurs in the small or large bowel § Ingested RBC – cherry red or green
o Cyst undergoes nuclear followed by a cytoplasmic § Cytoplasm – green
division – forms 8 trophozoites § Nuclear structures – dark red
o in the large intestine – trophozoites invade the • Nucleus
mucosal crypts and forms ulcers o Nuclear membrane – distinct line
§ flask shaped ulcer o Peripheral chromatin – layer of uniformly small
o hematogenous spread to other organs granules
§ liver – forms abscess o Karyosome – central, mass of chromatin

ENTAMOEBA HISTOLYTICA DIAGNOSTIC CHARACTERISTIC

THROPHOZOITES CYST

• 12 – 60 um diameter PRECYST
• Pseudopodia • Rounded form
• Cytoplasmic protrusion: • Single round nucleus

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UNSTAINED TROPHOZOITES • Progression : irregular trenches with hairlike remnants
• Ingestion of RBC o Buffalo skin
o Dyak hair ulcers
STANED TROPHOZOITES
• Fine uniform granules of peripheral chromatin Natural or innate immunity to E. histolytica
• small central karyosome in nucleus • in the intestines,
• ingested RBC o Mucin inhibition of amoebic attachment to the
• average size : 12 um underlying mucosal cell
• in the systemic circulation,
STAINED CYST o complement mediated killing of trophozoites
• typical nuclear structure
• chromatoidal bars with rounded or squared ends Acquired immunity to E. histolytica
• diameter: >10 um • primarily – cell mediated response
o humoral response may also contribute to anti-
PATHOGENESIS amoebic immunity
• activated T-cells kills E. histolytica by:
Mechanism of virulence:
o directly lysing trophozoites in a contact-dependent
• production of enzymes or other cytotoxic substances
process
• contact-dependent cell killing
o producing cytokines which activate macrophages and
• cytophagocytosis
other effector cells (neutrophils and eosinophils)
o providing helper effect for B-cell antibody production
in vitro – amoebic killing of target cultivated mammalian cells involve:
• interferon (IFN) and interleukin (IL-2) – may have role in
• receptor-mediated adherence of ameba to target cells
activating macrophages for amoebicidal activity
• amebic cytolysis of target cells
• nitric oxide (NO) – lethal to trophozoites
• amebic phagocytosis of killed or viable target cells
o TNF stimulates NO production
• Secretory IgA isolated in the gut – indicator of current or recent
Entamoeba histolytica - adhere to the colonic mucosa through a
invasive amoebiasis
galactose- inhibitable adherence lectin (Gal lectin).
• Then, the amebae kill mucosal cells by activation of their
caspase-3 AMOEBIC MODULATION OF HOST IMMUNE RESPONSE
• leading to their apoptotic death engulfment Immunosuppression characterized by T-cell hypo
during acute stage responsiveness, suppressed
of amoebiasis proliferation and cytokine production,
depressed delayed-type
hypersensitivity (DTH), and
macrophage suppression
• Which is favorable for amoebic
survival

ASYMPTOMATIC INFECTIONS
• Carrier state – cysts passed out in the stool
• Present in major cases

SYMPTOMATIC INFECTIONS
• Intestinal – most common, asymptomatic, vague and
nonspecific
o Dysenteric
§ Amoebic Colitis
• Penetration od muscularis mucosa to submucosa, causes: o Non-dysenteric colitis
o Flask shaped ulcer • Extraintestinal
§ Cecum, ascending colon and sigmoid o Hepatic
o Erosion of blood vessels § Acute nonsuppurative
§ Intraluminal bleeding § Liver abscess – most common
• Normal appearing mucosa despite undermining by coalescing o Pulmonary
ulcers o Other foci: Brain, Skin, Genital/Genito-urinary
• Necrosis and sloughing off of intestinal wall
Amoebic Colitis – presents as gradual onset of abdominal pain and
Sigmoidoscopy – show grossly normal mucosa between ulcers diarrhea with or without blood and mucus in the stools
• Differentiates amoebic dysentery from bacillary dysentery • Incubation period: 8 – 10 days

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• Presents with – diarrhea/dysentery, abdominal pain and • Hepatomegaly and tenderness
cramping, flatulence, anorexia, weight loss, chronic fatigue o Toxic response to infection
• Fever – not common, occurs in 1/3 of the patients • Hepatic infection
• Children - develop fulminant colitis with severe bloody o Reach the liver via portal vein
diarrhea, fever, and abdominal pain o (+) tenderness and enlargement
• Physical Examination o Fever, weight loss
o Abdominal tenderness over the: o Cough – RLL pneumonitis
§ Cecum
§ Transverse colon Amoebic Liver Abscess (ALA) – most common extra-intestinal form
§ Sigmoid of amoebiasis
• Composed of proteinaceous, necrotic debris of lysed
• (+) flask shaped ulcer hepatocytes and inflammatory cells
• (+) anchovy sauce-like content of abscess
• Acute presentation: less than 2 weeks duration
• Severely diseased colon • Chronic: more than 2 weeks duration
o Shows leakage • Cardinal manifestation:
into abdominal o Fever
cavity o Right upper quadrant (RUQ) pain
§ Distention o Other: increased pain severity, radiation to right
§ ileus and peritoneal gas shoulder, night sweats and increased WBC
• Most serious complication • Most frequent complaints, particularly in acute cases (<2
o Perforation – 60% of fulminant colitis cases weeks duration)
o Secondary bacterial peritonitis • Recurrence rate: 0.29%
• Most serious complication:
BACILLARY VS. AMOEBIC DYSENTERY o Ruptures into the pericardium with a mortality rate of
70%
o Rupture into the pleura with mortality of 15 to 30%
o Super infection
o Intraperitoneal rupture, which occurs in 2 to 7.5% of
cases - second most common complication
§ Not as serious as colonic perforation
because ALA is sterile
• Differential diagnosis:
o Pyogenic liver abscess
o Tuberculosis of the liver
o Hepatic CA

Pulmonary Amoebiasis – erosion of hepatic abscess through

diaphragm
• Subdiaphragmatic abscess – pleurisy, right lower lobe
pneumonitis
• Rupture through pleural cavity – effusion ascending the major
fissure
• Bronchial erosion – amoebas in sputum
• Primary pulmonary amoebiasis - hematogenous

Secondary Amoebic Meningoencephalitis – 1-2% occurrence

Ameboma – “napkin ring” deformity • Should be considered in cases of amebiasis with abnormal
• Occurs in less than 1% of intestinal infection mental status
• Presents as mass-like lesions with abdominal pain
• With history of dysentery • Renal involvement – due to extension of ALA or retroperitoneal
• Mistaken as carcinoma colonic perforation is rare
• Genital involvement - caused by fistulae from ALA and colitis
or primary infection through sexual transmission

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DIAGNOSIS METRONIDAZOLE
• MOA – reduction by ferrodoxin (reactive radical)
• Best used: stool antigen + serology
• SE – nausea, diarrhea, metallic state, headache
Stool Exam – nonspecific and insensitive • Can be given during the last 2 trimester of pregnancy
• From sigmoidoscopy • Precaution – abstinence from alcohol
• Direct fecal smears (DFS)
o Saline – observe for motility PREVENTION
o Saline and methylene blue – Entamoeba species • Break the chain of transmission
stains blue • Improve environmental sanitation
§ Differentiates them from WBC o Provide sanitary disposal of human feces
§ Reveals the nucleus and karyosome – used o Proper use of latrines
to differentiate E. histolytica to non • Practice of proper hygiene
pathologic amoeba o Hand washing
• Formalin-ether concentration test (FECT) • Safe dirking water and safe food
• Merthiolate-Iodine Formalin Concentration test (MIFC) o Boiling and adding iodine to drinking water
Culture – TYI-S-33 medium o Vegetable and fruits should be thoroughly washed
• Robinson’s and Inoki medium – more sensitive but not o Use of night soil for fertilizer should be avoided
routinely available • Food handlers
Serology – differentiate from non pathologic species o Screened for cyst carriage
• Indirect hemagglutination – more specific, positive for years o Asymptomatic cyst carrier: should be treated and
• ELISA – E. histolytica Gal/GalNAc lectin monitoring
• EIA • Vaccine – cost effective and potent strategy for amoebiasis
• DNA hybridization probes prevention and eradication
• PCR o Candidate vaccine molecules which have been most
UTZ, CT scan, MRI – non invasive, sensitive for early ALA intensely studied are:
§ serine-rich E. histolytica protein (SREHP)
EPIDEMIOLOGY § the adherence lectin (Gal/GalNAc lectin)
§ the 29 kDa cysteine-rich amebic antigen.
• Prevalence varies with level of sanitation
o However these has been utilized in animal model
o Higher - tropics and subtropics, developing countries,
crowded conditions
• Severity
o Greater - tropics and malnutrition
• Transmission
o By asymptomatic carriers – most important: food
handlers
o Contaminated water and food
• Cyst – relatively resistant
o Killed – drying, T >55C, super chlorination, adding
iodine to drinking water

TREATMENT
• Treatment goals:
o Cure invasive disease at both intestinal and
extraintestinal sites
o Eliminate the passage of cyst from intestinal lumen

Drug of choice:
• Asymptomatic intestinal amoebiasis – Diloxanide furoate
• Symptomatic: acute amoebic colitis – Metronidazole ,
Tinidazole, Secnidazole
o Followed by luminant agent
§ Eliminates intestinal colonization
§ Prevents relapse
• Hepatic abscess – metronidazole, tinidazole
o Aspiration and drainage

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