Paper I
Question
Difference between bacterial and amoebic dysentery. Add a note on morphology and lab diagnosis of E.histolytica (3+2+3)
Answer
Differences between bacillary (Shigella) and amoebic (Entamoeba histolytica) dysentery
| Feature | Bacillary dysentery | Amoebic dysentery |
|---|---|---|
| Onset | Sudden/acute | Gradual |
| Fever | Often present, can be high | Usually absent or low-grade |
| Stool character | Small volume, frequent, blood/mucus visible | Large volume, foul-smelling, “anchovy sauce”-like |
| Tenesmus | Prominent | Less prominent |
| Microscopy | Numerous faecal leukocytes | Trophozoites with ingested RBCs; few faecal leukocytes |
| Mucosal ulceration | Superficial, diffuse | Flask-shaped ulcers (narrow neck, broad base) |
| Extraintestinal spread | Rare | Liver (amoebic liver abscess) |
Morphology of Entamoeba histolytica Exists as a motile trophozoite (10–60 μm, characteristically shows ingested RBCs in invasive/pathogenic strains — the key diagnostic hallmark) and a resistant, infective cyst (round, mature cyst has 4 nuclei, contains rod-shaped chromatoid bodies with rounded ends in immature cysts).
Laboratory diagnosis of E. histolytica
- Stool microscopy — trophozoites (with ingested RBCs) in loose/dysenteric stool; cysts (quadrinucleate) in formed stool.
- Stool antigen ELISA — more sensitive, and can distinguish pathogenic E. histolytica from non-pathogenic E. dispar (morphologically identical).
- Serology — highly sensitive for extraintestinal (liver abscess) disease, since stool exam is often negative there.
- Imaging (ultrasound/CT) — for amoebic liver abscess.