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Case No. 26. LIM, YOONTAEK Clark. Case. EF, a fresh college graduate, is applying for a job at a pharmaceutical company. Routine laboratory examinations were requested. Fecalysis revealed: (+) E. histolitica Asymptomatic. Entamoeba histolytica.

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Case no 26

Case No. 26



Case no 26

  • EF, a fresh college graduate, is applying for a job at a pharmaceutical company.

  • Routine laboratory examinations were requested.

    • Fecalysis revealed: (+) E. histolitica

    • Asymptomatic

Entamoeba histolytica
Entamoeba histolytica

  • Protozoan parasite, cause of diarrhea, dysentery, liver abscess and other syndromes

  • Occurs primarily in developing countries, but immigrants, travelers, diagnosed with infection in U.S.

  • Must be distinguished clinically from Entamoeba dispar, a morphologically identical parasite that is non-invasive and does not cause disease

  • Onset of colitis usually gradual with symptoms > 1 wk, distinguishing it from bacterial dysentery

  • Infective stage : mature tetranucleated cyst


  • Polluted water supply

  • Unclean handling by injected individuals

  • Droppings of flies and other insects

  • Use of human excrement an vegetable gardens

  • Gross carelessness in personal hygiene

  • In homosexual acquired through sexual, anal intercourse

Sites of infection

  • Colon: dysentery, ameboma (tumor-like lesion of colonic lumen; can be confused radiographically with cecal cancer), toxic megacolon

  • Liver: abscess, can rupture causing peritonitis

  • Lung: empyema (right sided- direct extension from liver)

  • Heart: pericarditis (direct extension from liver)

  • Brain: abscess (hematogenous spread, rare)

  • Skin: usually perineal, genital

  • GU: recto-vaginal fistula

Diagnosis of amebic colitis
Diagnosis of amebic colitis

  • Observation of red cell-containing motile trophozoites on fresh stool smear (insensitive); always heme + stool

  • Colonoscopy: biopsy or scraping at margin of colonic mucosal ulcer: parasite may be seen; H&E shows necrosis, classic flask-shaped ulcer

  • Stool antigen test that distinguishes Eh from E. dispar is available, more sensitive than microscopy of stool

  • Serology 99% sens. for amebic liver abscess; 88% sens. for colitis, but Abs may be present yrs. later so that serology may not be useful in immigrants from Eh-endemic regions

  • Ultrasound of liver: cannot distinguish amebic from pyogenic abscess, but can guide aspiration if necessary

  • Liver abscess aspiration--yields anchovy paste-like material, lack of WBCs (due to lysis by parasite) clue to diagnosis, parasites usually not seen

Laboratory diagnosis
Laboratory Diagnosis

  • Microscopy

    • Microscopic identification of cysts and trophozoites in the stool is the common method

      • Fresh stool: wet mounts and permanently stained preparations (e.g., trichrome).

      • Concentrates from fresh stool: wet mounts, with or without iodine stain, and permanently stained preparations (e.g., trichrome).

    • E. histolytica trophozoites can also be identified in aspirates or biopsy samples obtained during colonoscopy or surgery

Trophozoites of entamoeba histolytica
Trophozoites of Entamoeba histolytica

Line drawing

Trichrome stain

Trophozoites of Entamoeba histolytica with ingested erythrocytes (trichrome stain)

Case no 26

  • Invasive form

  • Active, progressive, indirectional

  • Found in liquid stool

  • Eccenteric karyosome, “bulls eyes”

  • 1 nucleus

  • Presence of ingested RBC

  • Killed by exposure to air or stomack acid -> cannot cause infection

Cysts of entamoeba histolytica
Cysts of Entamoeba histolytica

Line drawing

Stained with trichrome

Wet mounts stained with iodine

Case no 26

  • Infective stage

  • Found in formed stool

  • 4 nuclei

  • Cigar-shape chromatoidal body

  • With glycogen mass


  • Immunodiagnosis

    • Antibody Detection; Enzyme immunoassay (EIA) kits for Entomoeba histolytica

      • 95% of patients with extraintestinal amebiasis

      • 70% of patients with active intestinal infection

      • 10% of asymptomatic persons who are passing cysts

      • Detectable E. histolytica-specific antibodies may persist for years after successful treatment, so the presence of antibodies does not necessarily indicate acute or current infection

    • Antigen Detection

      • Useful as an adjunct to microscopic diagnosis in detecting parasites and to distinguish between pathogenic and nonpathogenic infections


  • Molecular methods

    • PCR is the method of choice for discriminating between the pathogenic species (E. histolytica) from the nonpathogenic species (E. dispar)

Treatment of amoebiasis by rang
Treatment of amoebiasis by Rang

  • Acute invasive intestinal amoebiasis resulting in acute severe amoebic dysentery : metronidazole (or tindazole) followed by diloxanide

  • Chronic intestinal amoebiasis : diloxanide

  • Hepatic amoebiasis : metronidazole followed by diloxanide

  • Carrier state : diloxanide

Treatment for asymptomatic patient
Treatment for asymptomatic patient

  • Luminal agents alone should be used (not absorbed)

  • Iodoquinol: 650 mg tid x 20 days

  • Paromomycin: 25-35 mg/kg/d in 3 divided doses x 7 days

Metronidazole nitroimidazole
Metronidazole (nitroimidazole)

  • DOC for treatment of extraluminal amoebiasis

  • Kills trophozoites but has no effect on the cysts

  • Most effective drug available for invasive amoebiasis involving the intestine or the liver, but less against in the lumen of the gut

  • MOA : damage to the DNA of the trophozoite by toxic oxygen products generated from the drug

  • Pharmacokinetics

    • Given orally

    • Rapidly and completely absorbed.

    • Peak conc : 1~3 hours

    • T1/2 : 7 hours

    • Excreted in urine

  • Also used in Giardiasis (DOC), Trichomoniasis (DOC)

Metronidazole nitroimidazole1
Metronidazole (nitroimidazole)

  • S/E

    • Frequent: GI intolerance, metallic taste, headache, dark urine (harmless)

    • Occasional: peripheral neuropathy (with prolonged use, usually reversible), phlebitis at injection sites, disulfiram-like reaction with alcohol, insomnia, stomatitis.

  • Drug interaction

    • Disulfiram and ethanol : avoid co-administration

    • Barbiturates may decrease metronidazole levels


  • Lumninal agent

  • 90% not absorbed

  • Unknown mechanism

  • Effective for trophozoite in lumen but not in bowel wall or tissue

  • S/E

    • GIT

    • Increase protein bound iodine

    • Dermatitis, urticaria

    • Neurotoxin

    • Nephrotoxin

Diloxanide furoate
Diloxanide furoate

  • Luminal agent

  • Inactive against tissue trophozoite

  • Unknown mechanism

  • Direct amoebicidal action, affecting the amoebae before encystment

  • DOC for asymptomatic infection

  • No serious side effects

  • Contraindicated in pregnancy

  • S/E

    • Itchy rash (urticaria)

    • Itching (pruritus)

    • Excess gas in the stomach and intestines (flatulence)

    • Vomiting

Paromomycin sulfate
Paromomycin sulfate

  • An aminoglycoside

  • Luminal only

  • S/E

    • GIT

    • Renal toxicity

    • Caution with GIT ulceration since drug can be absorbed with more toxicity

Emetine dehydroemetine
Emetine & Dehydroemetine

  • For tissue trophozoite

  • Oral unreliable

  • IM or SC is preferred; never IV – toxic

  • Only for 3~5 days not more than 10days

  • Dehydroemetine is preferred (less tosic)

  • For severe amoebiasis where metronidazole cannot be used

  • Combine with luminal agent

  • S/E

    • Pain at injection site : sterile abscess

    • Arrythmia, CHF, hypotension

  • Contraindication

    • Cardiac disease

    • Renal disease ( cannot be excreted & may accumulated )

    • Young children & pregnancy