Amoebiasis lecture
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Amoebiasis is caused by the intestinal protozoan Entamoeba histolytica. Most infections are asymptomatic, but 10% can cause a spectrum of clinical syndromes ranging from asymptomatic to dysentery to liver and other organ abscesses. Transmission occurs through the fecal-oral route via contaminated food, water, or direct person-to-person contact. Diagnosis involves microscopic identification of trophozoites in stool or abscess samples and serologic detection of antibodies. Treatment depends on the infection site and involves luminal amoebicides for intestinal infection and tissue amoebicides like metronidazole for extra-intestinal infections such as liver abscesses.
![Luminal amoebicide
Diloxanide furoate
Paromomycin
Diiodohydroxiquin
Liver, gut wall and other tissues
Emetine
Dehydroemetine
Hepatic amoebicide
Chloroquine
Both tissue and intestinal amoebicide (Nitroimidazoles)
Metronidazole [500-800 mg TDS X 5 (5-10) days]
Tinidazole [ 2 gm OD X 1-3 days]
Ornidazole [ 2 gm OD X 1-3 days]
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Amoebiasis lecture
- 2. Amoebiasis is an infection with the intestinal protozoa Entamoeba histolytica. About 90% of infections are asymptomatic Remaining 10% produce a spectrum of clinical syndromes Ranging from - asymptomatic to dysentery to abscesses of liver or other organs
- 3. Entamoeba histolytica Trophozoites • • • • 10 - 60 μm in D Cytoplasm – # outer clear ectoplasm # inner granular endoplasm # food vacuoles with RBCs, leukocytes & tissue debris Motile by pseudopodial extensions Nucleus with central karyosome, surrounded by delicate membrane lined with chromatin granules
- 4. Entamoeba histolytica Precyst Intermediate form • Oval with blunt pseudopodia • No food vacuoles • Cysts • • • • • Spherical, 10 - 15 μm in D Uninucleate, later bi- or quadri- nucleate Thick chitinous wall Glycogen mass – not in quadrinucleate Chromidial or Chromatoid bars
- 5. World worldwide in distribution 3rd most common parasitic death India, China, Africa, South America 2-60% prevalence 100,000 deaths/yr 500 million infections 50 million cases India 15% prevalence (3.6-47.4%) variation according to sanitation
- 6. Source of infection is a case or carrier -1∙5 X 107 cysts per day Reservoir is only human – several years Resistant to chlorine in normal conc. Readily killed by freezing or heating(55 C)
- 8. All age groups affected No gender or racial differences Institutional, community living, MSM Severe if children, old, pregnant, PEM Develops antibodies in tissue invasion
- 9. Low socio-economic status Poor sanitation, sewage contamination Night soil for agriculture Seasonal variation
- 10. 1- 4 weeks 1- 4 weeks Faeco -oral route • contaminated water and food • direct hand to mouth Agency of flies, cockroaches, rats, etc. Sexual contact via oro -rectal route
- 11. Most common type of amoebic infection is asymptomatic cyst passage Intestinal amoebiasis – abdominal cramps with mild diarrhoea to colitis and dysentry Extra-intestinal amoebiasis – Amoebic liver abcess, rarely lungs, skin, genitalia and CNS are affected Amoeboma – inflammatory and edematous reaction around trophozoites
- 12. 90% without symptoms does not damage lumen flask shaped ulcers superficial or deep abd pain (tenesmus) diarrhoea, dysentery, fever peri-anal ulcers <0.5% severely ill with high fever intestinal bleeding, perforation paralytic ileus CFR-40% Uncommonly, a chronic form of amoebic colitis can be confused with inflammatory bowel disease
- 13. Pseudotumoral lesion Necrosis, edema and inflammatory thickening of mucosa and submucosa of intestinal wall 1% of cases palpable mass with trophozoites Always coexists with ulceration Single, rarely multiple in different parts of colon, on skin at site of ALA aspiration
- 14. Macroscopy Character Amoebic dysentry Bacillary dysentry Number 6-8 motions per day > 10 motions per day Amount Copious Small Odour Offensive Odourless Colour Dark red Bright red Acidic Alkaline Non-adherent Adherent Reaction Consistency
- 15. Microscopy Character Amoebic dysentry Bacillary dysentry In clumps Discrete or in Rouleaux Pus cells Few Numerous Macrophages Few Numerous, many have RBCs and may mimic EH Eosinophils Present Scarce Charcot-Leyden crystals Present Absent Pyknotic bodies Present Absent Ghost cells Absent Present Parasites Trophozoites of EH Absent Bacteria Many motile bacteria Few or Absent RBCs
- 16. Most common extra-intestinal presentation The parasite reaches liver via portal system Occurs within 5 mths of dysentery in 95% of cases But concomitant active diarrhea is seen in less than a third of cases Pain and point tenderness over right hypochondrium and fever Jaundice rare, pleural effusion is common Older pt. from endemic areas usually have chronic disease Right lobe is commonly affected, abscess of left lobe is more dangerous due to its proximity to heart –> rupture –> pericardial effusion Necrotic cavitary lesion filled with cellular debris and parasite trophozoites – Anchovy sauce pus
- 17. Rupture is the most dreaded complication It may spread to pleura, lungs, peritoneum, pericardium or open outside through the anterior abdominal wall Serous pleural effusion or contiguous spread from ALA Rupture from ALA into pleural space Hepato-bronchial fistula with necrotic material in sputum may mimic blood – trophozoites can be present CNS involvement – rare – hematogenous spread Genital ulcer can occur – by contiguous spread or hematogenous route
- 18. Adhesion Surface adhesins Gal/GalNAc Lectin Lipophosphoglycan like molecules Invasion Neuraminidase Phospholipase A1, A2, and L1 Metallocollagenase ATPase Cysteine protease Lysis Amoebopore – insertion of protein ion channels – cytolytic and bactericidal
- 19. E. dispar E. moshkovskii E. coli E. hartmanii E.gingivalis E. dispar is morphologically indistinguishable from E. histolytica and so is E. moshkovskii etc. Most asymptomatic cases of amoebic infestation are believed to be one of these two species The other species are also nonpathogenic but can be microscopically differentiated
- 20. E. histolytica E.coli 20-30 μm 20-50 μm Active, unidirectional, “purposeful motility” Sluggish, nonpurposeful Ectoplasm & endoplasm Not defined Cytoplasmic Inclusions RBC, leukocytes, tissue debris, no bacteria Bacteria and cell debris but no RBCs Nucleus Central karyosome, delicate membrane, fine chromatin grains Eccentric nucleus, coarse granules line a tough membrane Precyst Oval, 10-20 μm, blunt pseudopodium 20 μm, resembles E. histolytica precyst Spherical, 10-15 μm Spherical, 15-20 μm 1-4 1-8 Rounded Filamentous Trophozoite Size Motility Cytoplasm Cyst Size No. of nuclei Chromidial bars
- 21. Endolimax nana Iodamoeba buetschlii Commensals of the human gut Can be easily differentiated microscopically
- 22. Samples : Stool ( 3 consecutive samples) Biopsy material from the ulcers (colonoscopy or sigmoidoscopy) Aspirate from liver abcess Serum Pleural fluid Pericardial fluid Sputum
- 23. Both saline and iodine wet mounts are prepared Any motile trophozoite is better seen in saline mount Iodine mount stains the internal structures and is used to identify cysts Permanent stains can also be used to stain smears
- 24. Antibody Antigen detection detection ELISA ELISA Coagglutination IHA IFA Copro-antigen detection by ELISA is another recent and very useful method
- 25. Xenic media Locke-egg media ( NIH media – Locke’s modification of Boeck and Drbohlav media) Axenic media Robinson’s media Diamond media – TYI-S-33, YI-S, LYI-S-2 Monoxenic media
- 26. Locke’s solution ( per litre) * 8 gm NaCl 0.2 gm CaCl2 * 0.01gm MgCl2 2 gm NaH2PO4 * 0.4 gm NaHCO3 0.3 gm KH2PO4 Break surface-sterilised eggs in a sterile container, blend and filter To 45 ml of egg soln. add 12∙5 ml of Locke’s soln. 5-10 ml of this soln. is dispensed per tube and is solidified by inspissation Tubes are kept at an angle during solidification to form a slant The media is then overlayed with 6-10 ml of Locke’s soln. and stored Before inoculation, 0∙2 ml (1mg) of a stock soln. of rice starch (5mg/ml) is added to each tube
- 27. Polymerase Chain Reaction DNA probes 18 S rRNA gene sequencing for speciation A zymodeme comprises those Entamoeba strains that share the same electrophoretic pattern and mobility for certain enzymes like – malic enzyme, phosphoglucomutase, hexokinase, glucose phosphate isomerase, aldolase etc 24 different zymodemes – 21 of human strains Currently however only 3 zymodemes are attributed to EH one only for E. dispar
- 28. Luminal amoebicide Diloxanide furoate Paromomycin Diiodohydroxiquin Liver, gut wall and other tissues Emetine Dehydroemetine Hepatic amoebicide Chloroquine Both tissue and intestinal amoebicide (Nitroimidazoles) Metronidazole [500-800 mg TDS X 5 (5-10) days] Tinidazole [ 2 gm OD X 1-3 days] Ornidazole [ 2 gm OD X 1-3 days]