Question
A 22-year-old male came to the Medicine OPD with complaints of increased frequency of loose stools with blood and mucus since 2 days. (
- (a) What is the clinical diagnosis ( 1 mark(s)
- (b) What are the TWO common etiological agents ( 2 mark(s)
- (c) How do you differentiate the parasitic and bacterial agents causing the above condition?” ( 3 mark(s)
- (d) Draw neatly labeled diagrams of the morphological forms seen in stool of theparasitic etiological agent. (e) How does one get the above infection (f) Which is the infective stage to man (g) List the extra intestinal complication of this condition and its laboratory diagnosis (h) Name TWO drugs to treat the above condition 3 mark(s)
Answer
(a) Clinical diagnosis: Amoebic dysentery (dysenteric syndrome — bloody, mucoid, frequent loose stools).
(b) Two common etiological agents: Bacterial dysentery — Shigella species (bacillary dysentery); Parasitic dysentery — Entamoeba histolytica (amoebic dysentery).
(c) Differentiating parasitic (amoebic) from bacterial (bacillary) dysentery
| Feature | Amoebic (parasitic) | Bacillary (Shigella) |
|---|---|---|
| Onset | Gradual | Abrupt |
| Stool | Foul-smelling, acid pH, scanty mucus, blood streaks | Frequent, small-volume, mucus and blood mixed |
| Fever | Usually absent | Common, high-grade |
| Microscopy | Trophozoites with ingested RBCs | Numerous pus cells (neutrophils), few RBCs |
| Systemic toxicity | Minimal | Marked |
| Complication | Liver abscess | Toxic megacolon, HUS (in Shigella dysenteriae type 1) |
(d) Morphological forms in stool: Trophozoite — irregular amoeboid form (10–60 μm) with a single nucleus (central karyosome, peripheral chromatin beading) and, in the invasive/dysenteric form, ingested erythrocytes in the cytoplasm; and Cyst — spherical, 10–20 μm, with up to 4 nuclei (mature cyst), chromatoid bodies (bar-shaped, rounded ends) visible in immature cysts. (A neatly labeled hand-drawn diagram of these two forms would accompany a written examination answer; described here in text form as diagrams cannot be rendered.)
(e) Mode of acquisition: faeco-oral route, by ingestion of mature (quadrinucleate) cysts in faecally contaminated food or water.
(f) Infective stage to man: the mature quadrinucleate cyst.
(g) Extra-intestinal complications and laboratory diagnosis: Amoebic liver abscess — the most common extra-intestinal complication, diagnosed by ultrasound/CT imaging (anechoic/hypoechoic lesion, typically in the right lobe), serology (detection of anti-amoebic antibodies, e.g., by ELISA/IHA — usually strongly positive in liver abscess), and needle aspiration if required (classic “anchovy sauce” pus, usually amoeba-negative on direct microscopy of aspirate since trophozoites are at the abscess wall). Other extra-intestinal sites (rare): lung, brain, via haematogenous or direct spread.
(h) Two drugs to treat: Metronidazole (tissue amoebicide, for the acute invasive phase) followed by a luminal amoebicide such as Diloxanide furoate (or Paromomycin), to eliminate residual intraluminal cysts and prevent relapse/transmission.