Difference between 1) amoebic and bacillary dysentery 2)amoebic liver abscess and pyogenic liver abscess 3) polio vaccine injectable or oral 2nd yr mbbs microbiology refer harsh mohan
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Refer apurba sastri
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Differences for 2nd Year MBBS Microbiology
Note: Apurba Sastri's Essentials of Medical Microbiology is not in the library database, but the content below is sourced from equivalent standard textbooks (Murray's Medical Microbiology 9e, Jawetz Medical Microbiology 28e, Sleisenger & Fordtran, Robbins Pathology) which cover the same topics at the same depth.
1. Amoebic Dysentery vs Bacillary Dysentery
| Feature | Amoebic Dysentery | Bacillary Dysentery |
|---|---|---|
| Causative agent | Entamoeba histolytica (protozoan) | Shigella spp. (gram-negative bacteria) |
| Infective form | Cyst (ingested) → trophozoite in colon | Bacteria (very low infective dose: ~10 organisms) |
| Transmission | Fecal-oral; contaminated food/water; cysts resistant to gastric acid | Fecal-oral; person-to-person; food/water; sexually transmitted (MSM) |
| Incubation period | 1–4 weeks (may be months) | 1–3 days (short) |
| Site of attack | Cecum and ascending colon predominantly; also sigmoid, rectum, appendix | Colon (sigmoid/rectum predominantly); scattered ileal ulcers |
| Ulcer type | Flask-shaped ulcers (narrow neck, broad base in submucosa) | Superficial mucosal ulcers; microabscesses/crypt abscesses |
| Pathogenesis | Trophozoites attach → induce apoptosis → invade crypts → burrow laterally into lamina propria | Enters via M cells → escapes macrophages → invades enterocytes basolaterally via T3SS; actin polymerization for cell-to-cell spread |
| Stool character | Blood and mucus, fewer PMNs; "raspberry jelly" stools; offensive odor | Bloody mucoid stool with abundant PMNs (pus cells); classic dysentery |
| Fever | Low-grade or absent | High fever common; may have toxemia |
| Systemic toxicity | Usually mild | Marked (especially S. dysenteriae 1) |
| Tenesmus | Present | Marked |
| Extraintestinal spread | Liver abscess in ~40% (via portal vein); rarely lung, brain | Rare bacteremia (only in malnourished/immunocompromised children) |
| Complications | Liver abscess, ameboma, toxic megacolon | HUS (S. dysenteriae), reactive arthritis/Reiter syndrome (HLA-B27+), neurological signs, leukemoid reaction, intestinal perforation |
| Microscopy of stool | Trophozoites with ingested RBCs (hematophagous trophozoites) | No organisms visible; abundant PMNs and RBCs |
| Chronicity | Can become chronic; carrier state common | Self-limiting (~7 days in adults); rare chronic carriers |
| Treatment | Metronidazole 800 mg TID × 5–10 days + luminal agent (diloxanide furoate/paromomycin) | Ciprofloxacin or azithromycin; ORS; antimotility agents contraindicated |
| Serology | Anti-amebic antibodies (ELISA/IHA) positive | Not useful |
2. Amoebic Liver Abscess (ALA) vs Pyogenic Liver Abscess (PLA)
(Sleisenger & Fordtran Table 84.3)
| Feature | Amoebic Liver Abscess | Pyogenic Liver Abscess |
|---|---|---|
| Causative agent | Entamoeba histolytica | Mixed bacteria: E. coli, Klebsiella, streptococci, anaerobes |
| Source | Portal spread from colonic trophozoites | Biliary tract disease (commonest), portal pyemia from abdominal sepsis, direct extension |
| Number | Usually single | Often multiple |
| Location | Right lobe, near the diaphragm | Either lobe |
| Presentation | Acute (days to 2 weeks) | Subacute (weeks to months) |
| Age/Sex | Young adult males (10× more common in men than women); rare in children | Older men with biliary disease; no sex predominance |
| Onset | Acute RUQ pain + high fever; <10% give history of prior dysentery | Insidious; "swinging" hectic fever |
| Jaundice | Uncommon (moderate if present; poor prognosis) | Mild jaundice (more common due to biliary origin) |
| Pus character | "Anchovy paste" / "chocolate sauce" — reddish-brown, odourless | Foul-smelling yellow/green pus |
| Organisms in pus | Trophozoites rarely seen; sterile on culture | Bacteria isolated on culture |
| Serology | Positive (ELISA/IHA ~95% sensitivity) | Negative |
| Diagnosis | US/CT + serology | US/CT ± aspiration/culture |
| Diagnosis notes | Imaging cannot distinguish the two — serology is key differentiator | Blood cultures often positive; check for biliary cause |
| Response to metronidazole | Dramatic improvement within 96 hours | No response (antibiotics selected by culture) |
| Treatment | Metronidazole 750 mg TID × 7–10 days IV/oral, then luminal amebicide | Drainage (percutaneous or surgical) + IV antibiotics (piperacillin-tazobactam ± metronidazole) |
| Aspiration | Only if diagnosis uncertain, no response to Rx in 5–7 days, or left lobe abscess near pericardium | Routinely performed for diagnosis + therapy |
| Complications | Pleuropulmonary rupture, pericardial rupture (left lobe), peritoneal rupture | Septicemia, pleural effusion, subphrenic abscess |
| Prognosis | Good with early treatment | Higher mortality; depends on underlying disease |
3. Oral Polio Vaccine (OPV/Sabin) vs Injectable Polio Vaccine (IPV/Salk)
(Jawetz Medical Microbiology 28e; Murray's Medical Microbiology 9e)
| Feature | OPV (Oral Polio Vaccine) — Sabin | IPV (Inactivated Polio Vaccine) — Salk |
|---|---|---|
| Type | Live attenuated (trivalent) | Killed/Inactivated (trivalent) |
| Route | Oral (2 drops) | Intramuscular injection |
| Cell substrate | Monkey kidney cells | Monkey kidney cells (Vero cells) |
| Strains | Types 1, 2, 3 (attenuated by passage in non-human cells) | Types 1, 2, 3 (formalin-inactivated) |
| Immunity produced | Both serum IgG and secretory IgA (mucosal immunity) | Serum IgG only (no mucosal/intestinal immunity) |
| Gut immunity | Yes — prevents intestinal replication and fecal shedding → herd immunity | No — virus can still replicate in gut and be shed |
| Herd immunity | Excellent — vaccine virus spreads to contacts | Limited — does not spread to contacts |
| Seroconversion | High after 3 doses | High |
| Ease of administration | Easy — no needle, suitable for mass campaigns | Requires trained personnel and injection |
| Cost | Cheaper | More expensive |
| Stability | Requires cold chain; heat-labile | More stable than OPV |
| Main advantage | Induces gut immunity + herd immunity; ideal for eradication programs | No risk of VAPP; preferred in immunocompromised |
| Main disadvantage | VAPP (Vaccine-Associated Paralytic Poliomyelitis) — reversion to virulence (~1 per 2.5 million first doses); type 2 reverts most easily | No gut immunity; does not prevent fecal-oral spread |
| Vaccine-derived poliovirus (VDPV) | Can occur in under-immunized populations | Not possible |
| Use in immunocompromised | Contraindicated (risk of VAPP in recipient/contacts) | Safe — preferred |
| Current global use | Still used in endemic countries (Pakistan, Afghanistan) for eradication | Exclusively used in USA, UK, most developed countries since 2000 |
| India (UIP) | Both OPV + IPV (fractional IPV introduced 2016 in combination schedule) | Given at 6, 10, 14 weeks alongside OPV |
| Boosters | Multiple doses required due to interference among types | 4 doses (2, 4, 6–18 months, 4–6 years in US schedule) |
Key Memory Points:
- OPV → Oral, Outstanding gut immunity, Oh no VAPP risk
- IPV → Injectable, Immune but no gut immunity, Ideal for immunocompromised
- The switch from OPV to IPV in the US (2000) eliminated all domestic paralytic polio cases attributable to the vaccine itself
- For polio eradication globally, OPV remains indispensable because it interrupts fecal-oral transmission by inducing gut immunity — Medical Microbiology 9e; Jawetz Medical Microbiology 28e
Lab diagnosis 1) giardiasis 2)bacterial UTI, 3) syphillis
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