---

9. Anti-Androgens

• Steroidal: Cyproterone acetate (also a progestin; used in hirsutism, precocious puberty)
• Non-steroidal (pure): Flutamide, Bicalutamide, Enzalutamide (used in prostate cancer)
• Aldosterone antagonist with anti-androgen action: Spironolactone (used in PCOS, hirsutism)
• 5α-reductase inhibitors (indirect): Finasteride, Dutasteride

---

10. ⭐⭐⭐⭐⭐ Tamoxifen vs Raloxifene

STAR trial: Raloxifene = Tamoxifen in breast cancer prevention but with fewer uterine cancers and thromboembolic events.

---

11. ⭐⭐⭐⭐⭐ Ormeloxifene (Centchroman)

• Class: 3rd generation SERM (non-steroidal)
• MOA: Selective estrogen receptor modulator; causes asynchrony between ovulation and uterine endometrial maturation → prevents implantation
• Dose: 30 mg twice weekly for 3 months, then once weekly (oral)
• Uses:
  • Oral contraceptive (non-hormonal, no estrogen/progesterone)
  • Dysfunctional uterine bleeding (DUB)
• Advantages: No major hormonal side effects, not a hormone, taken weekly (good compliance)
• Side effects: Oligomenorrhea/amenorrhea, delayed periods, weight gain
• Contraindication: Pregnancy (teratogenic)

---

12. Synthetic Progestins

---

13. ⭐⭐⭐ Minipill (Progestogen-Only Pill)

• Contains only progestogen (norethisterone or levonorgestrel) in low dose
• Taken continuously, every day without a break
• MOA:
  1. Thickens cervical mucus → blocks sperm
  2. Renders endometrium atrophic → prevents implantation
  3. May inhibit ovulation (inconsistently)
• Advantages: Safe in breastfeeding mothers, women who cannot take estrogen (hypertension, DVT, smokers over 35)
• Disadvantages: Irregular bleeding, less effective than combined OCP, must be taken at same time daily
• Failure rate: ~1-3 per 100 women-years

---

14. ⭐⭐⭐ Parenteral Contraceptive Measures

---

15. ⭐⭐⭐ Rationale for Combining Estrogen + Progesterone in OCP

1. Better cycle control: Estrogen alone causes irregular bleeding; progesterone alone may cause breakthrough bleeding. Together they produce regular withdrawal bleeding.
2. Synergistic contraceptive effect: Estrogen suppresses FSH (prevents follicular development) + Progesterone suppresses LH (prevents ovulation) + thickens cervical mucus.
3. Lower dose possible: Combination allows lower individual doses of each hormone, reducing side effects.
4. Endometrial protection: Progesterone prevents estrogen-induced endometrial hyperplasia/cancer.
5. Reduced failure rate: Pearl index < 0.1 (nearly 100% effective).

---

16. ⭐⭐⭐ Oxytocin vs Ergometrine

---

17. ⭐⭐⭐⭐⭐ Tocolytics

---

18. Uterine Stimulants (Oxytocics)

---

19. Finasteride

• Class: 5α-reductase inhibitor (Type II isoenzyme)
• MOA: Inhibits conversion of testosterone → DHT (dihydrotestosterone); DHT is the active androgen in prostate and hair follicles
• Uses:
  • Benign prostatic hyperplasia (BPH) - reduces prostate size
  • Male pattern baldness (androgenic alopecia) - lower dose (1 mg)
• Effects: Reduces PSA by ~50%, reduces prostate volume by 20-30%
• Side effects: Decreased libido, erectile dysfunction, gynecomastia, decreased ejaculate volume
• Note: Dutasteride inhibits both Type I and II isoenzymes (more complete DHT suppression)

---

20. Teriparatide

• What it is: Recombinant human PTH (1-34 fragment); anabolic bone agent
• MOA: Intermittent PTH stimulates osteoblast activity > osteoclast activity → net bone formation (paradoxical - continuous PTH causes bone resorption, but pulsatile stimulates formation)
• Dose: 20 mcg SC once daily
• Use: Severe osteoporosis (postmenopausal, glucocorticoid-induced); patients with multiple fractures; when bisphosphonates fail
• Side effects: Nausea, leg cramps, dizziness, transient hypercalcemia; risk of osteosarcoma (seen in rat studies - black box warning; avoid in Paget's disease, prior radiation)
• Duration: Max 2 years

---

21. Pramlintide

• What it is: Synthetic amylin analog (amylin is co-secreted with insulin by pancreatic β-cells)
• MOA:
  1. Slows gastric emptying → reduces postprandial glucose spike
  2. Suppresses glucagon secretion (postprandial)
  3. Promotes satiety (acts on hindbrain amylin receptors) → weight loss
• Route: SC injection before each meal
• Use: Adjunct to mealtime insulin in Type 1 and Type 2 DM (not used alone)
• Side effects: Nausea (most common), vomiting, hypoglycemia (when combined with insulin - reduce insulin dose at initiation)
• Advantage: Weight loss (unlike insulin which causes weight gain)

---

1. ⭐⭐⭐ Oestrogen Preparations

Classification

• Estradiol (E2) - most potent natural estrogen
• Estrone (E1)
• Estriol (E3) - weakest; used in vaginal atrophy

• Steroidal: Ethinyl estradiol (EE) - highly potent; used in OCPs; highest VTE risk
• Non-steroidal: Diethylstilbestrol (DES) - synthetic; now obsolete due to teratogenicity

• Mixture of equine estrogens (equilin + estrone sulfate); used in HRT

Routes of Administration & Preparations

Uses

• Hormone replacement therapy (postmenopausal symptoms - hot flushes, vaginal atrophy)
• Oral contraceptives (combined with progestin)
• Dysfunctional uterine bleeding
• Primary amenorrhea, hypogonadism
• Prostate cancer (high-dose DES - anti-androgenic)
• Osteoporosis prevention

Important Pharmacokinetics

• Ethinyl estradiol is far more potent orally than estradiol because the 17α-ethinyl group prevents first-pass metabolism
• Transdermal route avoids first-pass metabolism → lower DVT risk than oral
• All estrogens bind to estrogen receptors (ERα, ERβ) in target tissues

---

2. ⭐⭐⭐⭐⭐ SERMs (Selective Estrogen Receptor Modulators)

Definition

Mechanism

• Bind to ERα and ERβ receptors
• Tissue-specific conformational change in ER determines agonist vs antagonist effect
• Differ from pure estrogen agonists and pure antagonists (like fulvestrant)

Classification & Tissue Effects

Key Clinical Points

• Tamoxifen → endometrial cancer risk (uterine agonism)
• Raloxifene → no endometrial cancer (uterine neutral)
• All SERMs → increased DVT/PE risk
• All SERMs → hot flushes as side effect
• STAR trial: Raloxifene = Tamoxifen for breast cancer prevention, but safer uterine profile

---

3. ⭐⭐⭐⭐⭐ Clomiphene Citrate

Drug Profile

• Class: SERM (non-steroidal); triphenylethylene derivative
• Available as: Mixture of two geometric isomers - enclomiphene (active, trans) + zuclomiphene (less active, cis)

Mechanism of Action

1. Binds to hypothalamic ER → blocks normal inhibitory feedback of estrogen on hypothalamus
2. Hypothalamus "perceives" low estrogen → increases GnRH pulse frequency and amplitude
3. ↑GnRH → ↑FSH and ↑LH secretion from pituitary
4. ↑FSH → follicular development and maturation → ovulation

Acts primarily at pituitary level - increases LH and FSH pulse amplitude without changing frequency

Pharmacokinetics

• Oral, well absorbed
• Long half-life (~5-7 days); stored in fat
• Zuclomiphene persists for weeks (accounts for anti-estrogenic side effects)

Dose & Regimen

• 50 mg/day × 5 days, starting on Day 2-5 of menstrual cycle
• If no response: increase to 100 mg/day × 5 days (max 150 mg)
• Ovulation expected 5-10 days after last dose

Uses

• Ovulation induction in anovulatory infertility (PCOS is commonest indication)
• Unexplained infertility
• WHO Group II anovulation

Side Effects

• Ovarian hyperstimulation syndrome (OHSS) - most serious
• Multiple pregnancy (twins ~8%, higher-order rare)
• Vasomotor symptoms (hot flushes)
• Visual disturbances (blurring, scotoma) → stop drug immediately
• Cervical mucus hostility (anti-estrogenic on endometrium/cervix)
• Ovarian cyst formation
• Abdominal bloating

Contraindications

• Liver disease
• Abnormal uterine bleeding (undiagnosed)
• Ovarian cysts (other than PCOS)
• Pregnancy
• Hormone-dependent tumors

Success Rate

• Ovulation in ~70-80%; pregnancy in ~30-40% (discordance due to anti-estrogenic effect on endometrium/cervical mucus)
• If no ovulation after 3 cycles at 150 mg → clomiphene resistant → use letrozole or gonadotropins

---

4. Aromatase Inhibitors (AIs)

Mechanism

• Aromatase (CYP19A1) is the enzyme that converts androgens (androstenedione, testosterone) → estrogens (estrone, estradiol) in peripheral tissues (fat, liver, muscle)
• AIs block aromatase → ↓estrogen synthesis (mainly in postmenopausal women where ovarian estrogen is absent and peripheral aromatization is the main source)

Classification

Uses

1. Breast cancer - adjuvant therapy in postmenopausal ER+ breast cancer (now first-line over tamoxifen in postmenopausal women)
2. Ovulation induction - Letrozole (off-label but now preferred over clomiphene in PCOS; better endometrial receptivity, no anti-estrogenic effect on uterus, less OHSS)
3. Endometriosis (letrozole)
4. Gynecomastia (anastrozole)

Side Effects

• Musculoskeletal pain/arthralgia (most common)
• Osteoporosis (significant - estrogen deprivation → bone loss; bisphosphonates often co-prescribed)
• Hot flushes
• Vaginal dryness
• Hypercholesterolemia
• Not for premenopausal women (ovarian aromatase not fully suppressed; can cause ovarian stimulation)

---

5. ⭐⭐⭐⭐⭐ Mifepristone (RU-486)

Drug Profile

• Class: Synthetic 19-norsteroid; analog of norethindrone
• Primary action: Competitive antagonist at progesterone receptors (high affinity - 5× greater than progesterone itself)
• Additional action: Anti-glucocorticoid (also antagonizes glucocorticoid receptors) and weak anti-androgenic

Mechanism of Action

1. Blocks progesterone receptors in decidua → decidual breakdown → detachment of conceptus
2. Increases uterine sensitivity to prostaglandins
3. Softens and dilates cervix
4. Combined with misoprostol (PGE1): prostaglandin causes uterine contractions → expulsion of products of conception

• Ripens cervix and sensitizes uterus to oxytocin

Dose Regimens

Efficacy

• Mifepristone alone: ~60-80% complete abortion
• Mifepristone + Misoprostol: >95% effective in first trimester

Uses

1. Medical termination of pregnancy (MTP) - up to 9 weeks
2. Emergency contraception
3. Cervical priming before surgical MTP or induction
4. Cushing's syndrome (hyperglycemia due to hypercortisolism)
5. Uterine leiomyomas (investigational)
6. Endometriosis (investigational)
7. Postcoital contraception

Side Effects

• Nausea, vomiting, diarrhea
• Abdominal cramping
• Heavy bleeding (expected; may need surgical intervention if incomplete)
• Prolonged bleeding
• Serious (rare): Fatal sepsis reported with Clostridium sordellii (rare, associated with vaginal misoprostol route)

Contraindications

• IUD in situ (remove first)
• Adrenal insufficiency (blocks glucocorticoid receptors)
• Long-term corticosteroid therapy
• Coagulopathy / anticoagulant use
• Ectopic pregnancy
• Unreliable for follow-up

Key Points to Remember

• Half-life: ~18 hours
• Progesterone maintains pregnancy - mifepristone blocks this → withdrawal of progesterone support
• The combination with misoprostol (a PGE1 analog that contracts uterus) is the gold standard for medical abortion
• Progesterone is the "hormone of pregnancy maintenance" - blocking it is the rationale

---

3. ⭐⭐⭐⭐⭐ Management of Heparin Overdose

Step 1: Stop Heparin Immediately

• UFH half-life is only 30-150 min (IV) → effect dissipates quickly
• Mild bleeding: simply discontinue heparin; observe with serial aPTT

Step 2: Antidote - Protamine Sulfate

• What it is: Mixture of basic (positively charged) polypeptides isolated from salmon sperm
• MOA: Protamine (basic) binds heparin (acidic, negatively charged) → forms stable inactive complex → cleared by RES
• Dose: 1 mg protamine neutralizes 100 units of heparin (given IV)
• Max single dose: 50 mg
• Rate: Slow IV infusion (not bolus) - over 10 minutes
• Limitation: Protamine only partially neutralizes LMWH (~60-75% of anti-Xa activity) and does NOT neutralize fondaparinux

Dose Calculation (UFH)

• Based on amount of residual heparin (accounting for its half-life of ~45 min IV)
• If heparin stopped 30 min ago → give ~50% of calculated dose
• SC heparin: may need repeated small infusions of protamine

Side Effects of Protamine

• Hypotension, bradycardia
• Anaphylactoid reaction (especially in patients with fish allergy or prior protamine exposure - e.g., protamine zinc insulin users)
• Pulmonary vasoconstriction

Additional Measures

• Fresh Frozen Plasma (FFP) if severe bleeding
• Monitor aPTT

---

4. ⭐⭐⭐⭐⭐ Management of Warfarin Overdose

Based on INR level and bleeding status:

Antidotes Explained

• Reverses warfarin by replenishing carboxylated clotting factors (II, VII, IX, X)
• Oral: onset 6-12 h; IV: onset 4-6 h
• IV preferred in serious bleeding (faster)
• Drawback: Slow onset - takes hours; makes patient "warfarin resistant" for days

• Contains all 4 Vitamin K-dependent factors (II, VII, IX, X) + Protein C & S
• Preferred over FFP - normalizes INR faster, smaller volume, no ABO matching needed
• Ideal for life-threatening bleeding, especially ICH

• Contains all clotting factors
• Used when PCC unavailable
• Drawback: large volume, risk of TRALI, volume overload, requires ABO matching

Key Points

• Always give Vitamin K alongside PCC/FFP (PCC is short-acting; Vitamin K prevents rebound coagulopathy)
• Monitor INR every 4-6 hours until normal
• Restart warfarin at lower dose once INR is therapeutic

---

5. ⭐⭐⭐ Advantages of LMWH over Unfractionated Heparin (UFH)

Mechanism Basis

• UFH has mixed molecular weights (3,000-30,000 Da); chains long enough to bridge thrombin AND Xa to antithrombin
• LMWH (mean ~5,000 Da) - chains too short to bridge thrombin → mainly inhibits Factor Xa only
• Less binding to non-specific plasma proteins → predictable response

Disadvantages of LMWH (important to know)

• Renally cleared → accumulates in renal failure (reduce dose if CrCl <30 mL/min; or switch to UFH)
• Protamine only partially reverses it (~60-75%)
• Monitoring (anti-Xa assay) needed in: renal failure, obesity, pregnancy, extremes of weight

---

6. ⭐⭐⭐ Anti-Fibrinolytic Drugs & Their Therapeutic Uses

3 Main Anti-Fibrinolytic Drugs

1. Tranexamic Acid (TXA)

• Class: Synthetic lysine analogue
• MOA: Competitively blocks lysine-binding sites on plasminogen → prevents plasminogen from binding to fibrin → plasmin cannot be formed → clot is protected from lysis
• Uses:
  • Trauma/surgical bleeding (CRASH-2 trial: reduces mortality in trauma)
  • Post-partum hemorrhage (PPH)
  • Heavy menstrual bleeding (oral)
  • Dental extractions in anticoagulated patients
  • Hereditary angioedema
  • Hemophilia (adjunct)
• Route: IV or oral

2. Epsilon-Aminocaproic Acid (EACA)

• Class: Synthetic lysine analogue (similar to TXA but less potent)
• MOA: Same as TXA - blocks lysine-binding sites on plasminogen, inhibits fibrinolysis
• Uses:
  • Cardiac surgery (CPB) - reduces perioperative bleeding
  • Subarachnoid hemorrhage (prevent rebleeding)
  • Urinary tract bleeding (fibrinolysin in urine)
  • Hemophilia (adjunct)
• Route: IV or oral

3. Aprotinin

• Class: Serine protease inhibitor (natural, from bovine lung)
• MOA: Directly inhibits plasmin (and also trypsin, kallikrein) → prevents fibrinolysis
• Uses:
  • Cardiac surgery (CPB) - most effective antifibrinolytic; reduces transfusion requirements
  • High-risk re-operative cardiac surgery
• Status: Withdrawn in 2008 (BART trial: increased mortality/renal failure) → re-approved in some countries for specific high-risk cardiac surgery with restrictions

Summary Table

---

Contraindications of Thrombolytic Therapy

---

ABSOLUTE CONTRAINDICATIONS

---

RELATIVE CONTRAINDICATIONS

---

Memory Aid for Absolute CIs - "H-S-C-S-G-B"

Haemorrhagic stroke (ever) | Stroke <6 months | CNS tumour/damage | Surgery/trauma <3 weeks | GI bleed <1 month | Bleeding diathesis

---

Additional Notes

• For STEMI thrombolysis, additional absolute CIs include: aortic dissection (suspected), previous allergic reaction to streptokinase (for streptokinase specifically - do not repeat within 6-12 months due to antibody formation)
• Bleeding risk is doubled compared to anticoagulation alone: major bleeding ~9% vs 3%; intracranial haemorrhage ~1.5% vs 0.2%
• In life-threatening PE with haemodynamic collapse, absolute CIs may be overridden as a last resort (benefit > risk)

---

Classification of Ovarian Tumors

---

I. SURFACE EPITHELIAL-STROMAL TUMORS (~65-70% of all ovarian tumors; most common)

Serous cystadenocarcinoma = most common malignant ovarian tumor

---

II. SEX CORD-STROMAL TUMORS (~8%)

• Granulosa cell tumor - secretes estrogen → feminizing; associated with endometrial hyperplasia/carcinoma
• Thecoma / Fibrothecoma - usually benign; estrogen secreting
• Fibroma - benign; associated with Meigs syndrome (ascites + pleural effusion + ovarian fibroma)
• Sertoli-Leydig cell tumor (Androblastoma) - secretes androgens → virilizing
• Steroid (lipid) cell tumors

---

III. GERM CELL TUMORS (~15-20%; most common in young women/children)

---

IV. METASTATIC TUMORS (~5%)

• Krukenberg tumor - bilateral metastasis from gastric carcinoma (mucin-secreting signet ring cells)
• Also from: colorectal, appendiceal, breast, endometrial primaries

---

Quick Summary Table

---

1. ⭐⭐⭐ Cimetidine vs Ranitidine

---

2. ⭐⭐⭐⭐⭐ Sucralfate

Drug Profile

• Class: Basic aluminium salt of sucrose octasulfate (not an antacid)
• Requires acid to work (pH <4) → not combined with antacids/PPIs

Mechanism of Action

1. In acidic environment → polymerizes → forms a viscous, sticky gel
2. Gel binds selectively to ulcer crater (binds to positively charged proteins in necrotic tissue) → physical barrier over ulcer
3. Protects from acid, pepsin, and bile salts
4. Adsorbs pepsin and bile acids → inactivates them
5. Stimulates prostaglandin synthesis → mucosal protection
6. Stimulates mucus and bicarbonate secretion
7. May inhibit H. pylori growth
8. Enhances epithelial growth factor (EGF) binding

Uses

• Peptic ulcer disease (duodenal > gastric)
• Stress ulcer prophylaxis (ICU patients on ventilators)
• GERD (mild)
• Radiation-induced mucositis/esophagitis
• Aphthous ulcers (topical)
• Nasogastric tube ulcers

Side Effects

• Constipation (most common - due to aluminium)
• Aluminium toxicity (accumulation in renal failure)
• Nausea, dry mouth
• Drug interactions: Reduces absorption of fluoroquinolones, tetracyclines, phenytoin, digoxin, warfarin → give sucralfate 2 hours after other drugs

Advantages

• Minimal systemic absorption
• Safe in pregnancy
• Does not alter gastric pH → no rebound acid hypersecretion

---

3. ⭐⭐⭐ 6 Drugs Used in GERD

---

4. ⭐⭐⭐ Drugs for Dissolution of Gallstones

1. Ursodeoxycholic Acid (UDCA / Ursodiol)

• MOA:
  • Reduces biliary cholesterol secretion
  • Desaturates bile (makes bile less lithogenic)
  • Dissolves cholesterol crystals directly
• Dose: 8-10 mg/kg/day (or 15 mg/kg/day) orally in divided doses at night
• Efficacy: Complete dissolution in ~30% over 6-24 months; recurrence rate high (~50% in 5 years)
• Also used for: Primary biliary cirrhosis, intrahepatic cholestasis of pregnancy

2. Chenodeoxycholic Acid (CDCA)

• MOA: Similar to UDCA - reduces cholesterol synthesis in liver
• More side effects (diarrhoea, hepatotoxicity) → largely replaced by UDCA

3. Methyl tert-butyl ether (MTBE)

• Instilled directly into gallbladder via percutaneous catheter
• Rapidly dissolves cholesterol stones
• Used rarely (highly flammable, toxic)

---

5. ⭐⭐⭐⭐⭐ Reasons for Combining Antacids

---

6. ⭐⭐⭐⭐⭐ 6 Prokinetics

---

7. ⭐⭐⭐ 3 Digestants & Their Therapeutic Uses

---

8. ⭐⭐⭐⭐⭐ 6 Antiemetics

---

11. ⭐⭐⭐ Role of Probiotics in Diarrhoea

Mechanisms

1. Compete with pathogens for colonization sites and nutrients (competitive exclusion)
2. Produce lactic acid and bacteriocins → lower pH → inhibit pathogen growth
3. Strengthen gut mucosal barrier → reduce intestinal permeability
4. Modulate immune response → stimulate secretory IgA, regulate cytokines
5. Restore normal flora after antibiotic-associated dysbiosis

Clinical Uses in Diarrhoea

• Dose: Lactobacillus GG 10¹⁰ CFU/day; S. boulardii 250-500 mg/day
• Safe in healthy individuals; caution in immunocompromised (risk of bacteraemia)

---

12. ⭐⭐⭐⭐⭐ Role of Zinc in Paediatric Diarrhoea

Rationale

• Diarrhoea causes significant zinc losses in stool
• Zinc deficiency impairs immune function and intestinal repair

Mechanisms of Action

1. Enhances intestinal epithelial repair and mucosal integrity
2. Improves immune response (T-cell function, antibody production)
3. Reduces intestinal fluid and electrolyte secretion (anti-secretory effect)
4. Reduces intestinal permeability
5. Improves brush border enzyme activity (Na-glucose transporter function)

WHO/UNICEF Recommendation

• Given along with ORS, not as a replacement
• Reduces duration of diarrhoeal episode by ~25%
• Reduces severity and stool frequency
• Reduces risk of recurrence over next 2-3 months (residual protection)
• Meta-analyses confirm: reduces all-cause mortality in children in low/middle-income countries

---

13. ⭐⭐⭐⭐⭐ ORS - Composition, Preparation & Uses

WHO Reduced-Osmolarity ORS (2002 formulation)

Preparation

• Dissolve all salts in 1 litre of clean (boiled and cooled) water
• Use within 24 hours of preparation; discard remainder
• Home-made ORS: 1 litre water + 6 level teaspoons sugar + ½ teaspoon salt (approximate)

Mechanism

• Glucose-sodium co-transport (SGLT1): Glucose actively transports Na⁺ across the gut epithelium even during secretory diarrhoea → water follows osmotically → net absorption
• This mechanism is unaffected by cholera toxin (which causes secretion of Cl⁻/water but leaves SGLT1 intact)

Therapeutic Uses

1. Acute diarrhoea (dehydration prevention and treatment) - cornerstone of management
2. Cholera - oral rehydration (IV fluids if severe)
3. Rotavirus and other infectious diarrhoeas
4. Vomiting with mild-moderate dehydration (give small, frequent sips)
5. Post-gastroenteritis rehydration in children

---

14. ⭐⭐⭐ Pharmacotherapy for IBD

Crohn's Disease & Ulcerative Colitis

• Sulfasalazine = 5-ASA + sulfapyridine (carrier); sulfapyridine causes side effects
• Mesalazine = 5-ASA alone; better tolerated; used topically (enema/suppository) in distal UC
• Budesonide = topical steroid for ileal/right-colon CD (less systemic side effects)

---

15. ⭐⭐⭐ Choice of Laxatives in Elderly

Preferred Laxatives in Elderly

Avoid in Elderly

• Stimulant laxatives (senna, bisacodyl) - long-term use → atonic colon ("cathartic colon"), electrolyte disturbances, dependence
• Saline laxatives (Mg sulphate) - electrolyte disturbances, renal impairment risk
• Liquid paraffin - aspiration pneumonia risk, fat-soluble vitamin malabsorption, anal seepage

---

16. ⭐⭐⭐⭐⭐ Non-Diarrhoeal Uses of ORS

---

1. ⭐⭐⭐⭐⭐ HACEK Endocarditis

• Normal flora of upper respiratory tract/oral cavity
• Cause indolent (slow-growing), culture-negative endocarditis
• Require 5-10% CO₂ for growth; fail to grow on MacConkey agar
• Account for 0.8-6% of all infective endocarditis
• Typically on native/prosthetic valves with prior dental procedures
• Form large vegetations → high risk of embolization
• Treatment: Ceftriaxone 2g/day IV × 4 weeks (native valve); 6 weeks (prosthetic)

---

2. ⭐⭐⭐⭐⭐ Post Kala-Azar Dermal Leishmaniasis (PKDL)

• Caused by: Leishmania donovani
• Follows treated/untreated visceral leishmaniasis (kala-azar)
• Onset: 6 months - 3 years after apparent cure (India); during or immediately after treatment (Africa/Sudan)
• Lesions: Begin as hypopigmented macules → progress to erythematous patches → nodules and plaques on face, trunk, limbs (spares palms/soles)
• Significance: Patient acts as reservoir for sandfly transmission → sustains transmission even after kala-azar elimination
• Diagnosis: Clinical + slit-skin smear or biopsy showing amastigotes (LD bodies); rK39 test
• Treatment (India): Miltefosine (oral) × 12 weeks; Amphotericin B (refractory)
• No systemic symptoms - distinguish from kala-azar

---

3. ⭐⭐⭐ Kyasanur Forest Disease (KFD)

• Caused by: Kyasanur Forest Disease virus (KFDV) - Flavivirus (RNA virus)
• Vector: Hard tick Haemaphysalis spinigera
• Reservoir: Small mammals (rodents, monkeys); monkey deaths = warning sign of outbreak
• Geography: Karnataka (Kyasanur forest), India; endemic
• Features:
  • Abrupt fever, headache, myalgia, hemorrhagic manifestations (bleeding from nose/gums)
  • Biphasic illness: febrile phase → brief remission → neurological phase (2nd phase; meningoencephalitis)
  • Leukopenia, thrombocytopenia
• Diagnosis: Virus isolation; ELISA (IgM/IgG); RT-PCR
• Treatment: Supportive; no specific antiviral
• Prevention: Formalin-inactivated vaccine available (India); tick control

---

4. ⭐⭐⭐ Cat Scratch Disease (CSD)

• Caused by: Bartonella henselae (facultative intracellular Gram-negative bacillus)
• Vector/Reservoir: Cat flea (Ctenocephalides felis); cats (especially kittens) are reservoir
• Transmission: Scratch or bite of infected cat → inoculation of flea faeces
• Features:
  • Primary papule/pustule at site of scratch (3-10 days)
  • Regional lymphadenopathy (axillary, cervical) - tender, may suppurate → most characteristic feature
  • Low-grade fever, malaise
• Atypical/Severe forms: Parinaud oculoglandular syndrome (conjunctivitis + preauricular LN), encephalopathy, hepatosplenitis, bacillary angiomatosis (in HIV patients)
• Diagnosis: Clinical + Warthin-Starry silver stain (histology); Bartonella serology; PCR
• Treatment: Self-limiting in immunocompetent; Azithromycin shortens duration; Doxycycline/Rifampicin for severe cases

---

5. ⭐⭐⭐⭐⭐ 6 Microorganisms Causing Anaemia

---

6. ⭐⭐⭐ Epidemic Typhus

• Caused by: Rickettsia prowazekii
• Vector: Human body louse Pediculus humanus corporis (louse-borne)
• Transmission: Infected louse faeces rubbed into bite wound or mucosae (not direct louse bite)
• Features:
  • Sudden high fever (39-41°C), severe headache, myalgia
  • Rash: Maculopapular, day 5-6, starts on trunk → spreads centrifugally (spares face, palms, soles)
  • Altered sensorium, delirium
  • Can progress to vascular collapse, gangrene
• Diagnosis: Weil-Felix reaction (OX-19 positive, OX-2 positive, OX-K negative); ELISA; IFA
• Treatment: Doxycycline 100 mg BD × 7 days (drug of choice); Chloramphenicol
• Brill-Zinsser disease = Recrudescence of epidemic typhus years later (see Q31)
• Prevention: Delousing (DDT powder), tetracycline prophylaxis

---

7. ⭐⭐⭐⭐⭐ Procedure for Blood Culture Specimen Collection

When to Collect

• Before starting antibiotics; during fever spikes/chills (bacteraemia highest)
• At least 2-3 sets from different sites × different times

Procedure (Aseptic technique is critical)

• Explain procedure, take consent
• Gather: blood culture bottles (aerobic + anaerobic), syringes, needles, gloves, antiseptic

• Select antecubital vein
• Clean skin with 70% isopropyl alcohol → allow to dry
• Apply 1-2% povidone-iodine in concentric circles → allow to dry 60 seconds
• Do NOT re-palpate vein after cleaning (use sterile gloves)

• Disinfect rubber stopper of culture bottle with 70% alcohol → allow to dry

• Collect 8-10 mL blood in adults (1-3 mL in children) per set
• In adults: 5 mL into aerobic bottle + 5 mL into anaerobic bottle

• Inoculate bottles at bedside (reduces contamination)
• Gently mix by inversion

• Label: patient name, date, time, site, clinical details
• Transport to lab immediately at room temperature (do NOT refrigerate)
• Incubate at 37°C (BACTEC/BacT/Alert systems detect CO₂ production)

• Collect 2-3 sets, 30-60 min apart (or simultaneously for critically ill)
• Sensitivity with 3 sets = ~97-99%

Castañeda's Method (for brucellosis - see Q30)

---

8. ⭐⭐⭐ Fever of Unknown Origin (FUO)

Definition (Petersdorf & Beeson, 1961; revised)

• Fever >38.3°C (101°F) on several occasions
• Duration >3 weeks
• No diagnosis after 1 week of intensive inpatient investigation (or 3 outpatient visits / 3 days of hospitalization)

Classification of Causes (Durack & Street, 1991)

Organisms Causing FUO

• Bacteria: Salmonella typhi, Brucella, TB (M. tuberculosis), Listeria, endocarditis organisms, Bartonella
• Viruses: EBV, CMV, HIV
• Fungi: Histoplasma, Cryptococcus
• Parasites: Toxoplasma, Leishmania, malaria

---

9. ⭐⭐⭐⭐⭐ Relapsing Fever

Types

Clinical Features

• Sudden onset: High fever (39-40°C), severe headache, rigors, myalgia, arthralgia
• Hepatosplenomegaly, jaundice, petechial rash
• After 3-7 days: crisis (temperature spike + profuse sweating) → afebrile for 7-9 days → relapse
• Louse-borne: 1-2 relapses; Tick-borne: 3-10 relapses
• Mechanism of relapse: Antigenic variation of outer membrane proteins (Vmps) → evades antibodies → new bacteraemia

Diagnosis

• Peripheral blood smear (Giemsa/Wright stain) during febrile phase → motile spirochetes visible
• Thick and thin smear; dark-field microscopy

Treatment

• Doxycycline (single dose 100 mg for louse-borne; 7 days for tick-borne)
• Penicillin G (alternative)
• Jarisch-Herxheimer reaction - fever spike + rigors after first dose (spirochete lysis) → manage with antipyretics

---

10. ⭐⭐⭐⭐⭐ LD Bodies (Leishman-Donovan Bodies)

• What they are: Amastigote form of Leishmania donovani seen intracellularly within macrophages (mononuclear phagocytes)
• Named after: Sir William Leishman and Charles Donovan (independently discovered, 1903)
• Morphology:
  • Oval, 2-4 µm
  • Two distinct structures: large nucleus + rod-shaped kinetoplast (contains mitochondrial DNA)
  • Seen inside macrophages in clusters
• Where found:
  • Bone marrow aspirate (most common diagnostic site in India)
  • Spleen aspirate (most sensitive - 93-99% but risky)
  • Liver biopsy
  • Lymph node aspirate
  • Peripheral blood buffy coat (in immunocompromised)
  • Slit-skin smear (in PKDL)
• Stain: Leishman stain or Giemsa stain
• Significance: Demonstration of LD bodies = definitive diagnosis of visceral leishmaniasis

---

11. ⭐⭐⭐ Kauffmann-White Classification

• Purpose: Antigenic classification of the genus Salmonella based on surface antigens
• Based on 3 antigens:

• Formula notation: O antigen : H antigen phase 1 : H antigen phase 2
• Example: S. Typhi = O:9,12 : d : - (Group D, Vi+)
• S. Paratyphi A = O:1,2,12 : a : -
• S. Typhimurium = O:1,4,[5],12 : i : 1,2

---

12. ⭐⭐⭐ Carriers of Typhoid

• Gallbladder (most common) → bile → faecal carriage; associated with gallstones
• Urinary tract (rare; especially in S. haematobium co-infection)

---

13. ⭐⭐⭐ Lyme Disease

• Caused by: Borrelia burgdorferi (spirochete)
• Vector: Hard tick Ixodes scapularis (deer tick, USA); I. ricinus (Europe)
• Reservoir: White-footed mouse; white-tailed deer
• Stage 1 (Early localised, days-weeks):
  • Erythema migrans - pathognomonic; expanding bull's-eye rash at bite site (>5 cm); warm, not painful
  • Flu-like symptoms: fever, headache, myalgia, fatigue
• Stage 2 (Early disseminated, weeks-months):
  • Neurological (Lyme neuroborreliosis): Facial palsy (bilateral), meningitis, radiculopathy
  • Cardiac: Heart block (AV block), myocarditis
  • Multiple erythema migrans lesions
• Stage 3 (Late, months-years):
  • Lyme arthritis - large joint (knee), migratory, oligoarticular
  • Chronic neurological manifestations
• Diagnosis: ELISA (screening) → Western blot (confirmatory); 2-tier testing
• Treatment: Doxycycline 100 mg BD × 14-21 days (early); IV Ceftriaxone (neuro/cardiac)

---

14. ⭐⭐⭐ Sepsis Definition & SOFA Score

Definition (Sepsis-3, 2016)

• Sepsis: Life-threatening organ dysfunction caused by a dysregulated host response to infection
• Operationally: suspected infection + acute rise in SOFA score ≥2
• Septic shock: Sepsis + vasopressor requirement to maintain MAP ≥65 mmHg + serum lactate >2 mmol/L despite adequate fluid resuscitation (mortality >40%)

SOFA Score (Sequential Organ Failure Assessment)

• Max score = 24; baseline SOFA 0 (normal)
• Acute rise ≥2 = organ dysfunction = sepsis
• qSOFA (quick SOFA): Bedside screening - RR≥22, altered mentation, SBP≤100 → ≥2 = high risk

---

15. ⭐⭐⭐ Trench Fever

• Caused by: Bartonella quintana
• Vector: Human body louse Pediculus humanus corporis (same as epidemic typhus)
• Transmission: Louse faeces inoculated into abraded skin (not direct louse bite)
• History: Major problem in WWI (500,000+ soldiers affected)
• Clinical Features:
  • Quintana fever - recurring fever every 5 days (quintana = fifth)
  • Sudden onset: high fever, severe headache, pain behind eyes, shin bone pain (tibial pain = distinctive feature)
  • Rash (maculopapular, transient)
  • Relapsing course: 5-6 relapses possible
• Diagnosis: Blood culture (fastidious; needs special media); serology (ELISA, IFA); PCR
• Modern relevance: Seen in homeless/marginalized populations and HIV patients (bacillary angiomatosis, endocarditis caused by B. quintana)
• Treatment: Doxycycline + Gentamicin (endocarditis); Doxycycline alone (uncomplicated)

---

16. Chikungunya

• Caused by: Chikungunya virus (Togaviridae, alphavirus; RNA)
• Vector: Aedes aegypti and Aedes albopictus
• Name: Makonde word = "that which bends up" (due to stooped posture from joint pain)
• Features:
  • Sudden high fever, severe arthralgia (bilateral, symmetrical, small joints of hands/feet) - most characteristic
  • Maculopapular rash
  • No haemorrhagic manifestations (unlike dengue)
  • Arthralgia may persist months to years
• Diagnosis: RT-PCR (acute phase, <5 days); IgM ELISA (>5 days); plaque reduction neutralization
• Treatment: Supportive; NSAIDs/chloroquine for arthralgia; no vaccine
• Differentiate from dengue: Chikungunya = prominent arthralgia, no thrombocytopenia; Dengue = haemorrhage, thrombocytopenia

---

17. ⭐⭐⭐ Chagas' Disease (American Trypanosomiasis)

• Caused by: Trypanosoma cruzi
• Vector: Reduviid (triatomine) bug - Triatoma infestans ("kissing bug" / barber bug)
• Transmission: Bug defecates while feeding → trypomastigotes in faeces → rubbed into bite wound or mucosa
• Reservoir: Domestic and wild animals (dogs, cats, rodents, armadillos)
• Phases:
  • Acute phase: Chagoma (skin lesion at entry), Romaña's sign (unilateral painless periorbital oedema - conjunctival entry), fever, lymphadenopathy
  • Chronic phase (years later): Chagas cardiomyopathy (dilated cardiomyopathy, arrhythmias, heart block, sudden death), Megaoesophagus and Megacolon (autonomic ganglion destruction)
• Diagnosis: Peripheral blood smear (acute - trypomastigotes with C/U-shaped body); serology (chronic); xenodiagnosis
• Treatment: Benznidazole or Nifurtimox (effective only in acute phase)

---

18. ⭐⭐⭐ Bancroftian vs Brugian Filariasis

---

19. African Sleeping Sickness (Human African Trypanosomiasis)

• Caused by: Trypanosoma brucei gambiense (West Africa - chronic) and T. b. rhodesiense (East Africa - acute)
• Vector: Tsetse fly (Glossina spp.) - both sexes bite
• Stages:
  • Stage 1 (haemolymphatic): Chancre at bite site, fever, lymphadenopathy, Winterbottom's sign (posterior cervical lymphadenopathy - gambiense), hepatosplenomegaly
  • Stage 2 (meningoencephalitic): Crosses BBB → personality changes, reversal of sleep-wake cycle, progressive drowsiness → coma → death
• Diagnosis: Smear (blood/lymph node aspirate/CSF); CATT test; CSF pleocytosis
• Treatment:
  • Stage 1: Pentamidine (gambiense); Suramin (rhodesiense)
  • Stage 2: Melarsoprol (arsenic derivative - both; CNS penetration); Eflornithine (gambiense only)

---

20. Carriers of Salmonella (same as Q12 - see above)

• Urban carrier: Flies can carry Salmonella mechanically
• Animal reservoir carriers: Poultry, cattle, pigs (zoonotic Salmonella serovars)
• Epidemiologically, chronic human faecal carrier = most important for typhoid control

---

21. ⭐⭐⭐⭐⭐ Quantitative Buffy Coat (QBC)

• Principle: Blood is centrifuged in a capillary tube coated with acridine orange (fluorescent dye) + potassium oxalate → parasites in buffy coat concentrate and fluoresce
• Method:
  1. Collect capillary blood in heparinized QBC tube
  2. Centrifuge at high speed → layers form: RBCs (bottom) → buffy coat (WBCs + platelets) → plasma (top)
  3. Malaria parasites concentrate just above the RBC layer (expanded buffy coat zone)
  4. Acridine orange stains nucleic acid (DNA/RNA) of parasites → fluoresce bright green/yellow under UV fluorescence microscope
  5. Plastic float maintains tube expansion for examination
• Advantages:
  • More sensitive than thick blood smear (10× concentration)
  • Faster (15-20 min)
  • Can detect all Plasmodium species
  • Also detects Trypanosoma, Borrelia, microfilaria
• Disadvantages:
  • Cannot reliably differentiate Plasmodium species (speciation difficult)
  • Requires fluorescence microscope (expensive)
  • Cannot assess parasite density quantitatively
  • Cannot detect gametocytes reliably

---

22. ⭐⭐⭐⭐⭐ 6 Dimorphic Fungi

---

23. ⭐⭐⭐⭐⭐ 6 Fungi Causing Opportunistic Mycoses

---

24. ⭐⭐⭐ TRI-DOT Test

• Full name: Tri-Dot Immunoassay (also called ICT - Immunochromatographic test)
• Used for: Rapid diagnosis of malaria
• Principle: Lateral flow immunochromatographic assay detecting malaria-specific antigens in blood
• Antigens detected:
  • HRP-2 (Histidine-rich protein-2) → specific for P. falciparum
  • pLDH (Plasmodium lactate dehydrogenase) → detects all Plasmodium spp.
• Procedure:
  1. One drop of blood + buffer on nitrocellulose strip
  2. Antigens migrate → bind labelled antibodies → appear as coloured band
  3. Read in 15-20 minutes
• Interpretation:
  • Control band only = negative
  • Control + Test band (HRP-2) = P. falciparum
  • Control + pLDH band = non-falciparum
  • All 3 bands = mixed infection
• Advantages: Rapid (15-20 min), no microscopy needed, point-of-care use
• Limitations: Cannot assess parasite density; persists positive for weeks after treatment (HRP-2)

---

25. ⭐⭐⭐⭐⭐ Weil-Felix Test

• Principle: Heterophile agglutination - rickettsial patients develop antibodies that cross-react with antigens of Proteus species (OX-19, OX-2, OX-K strains) due to shared polysaccharide antigens
• Antigens used: Proteus vulgaris OX-19, Proteus vulgaris OX-2, Proteus mirabilis OX-K

• Titre ≥1:80 or 4-fold rise = significant
• Limitations: Not specific (Proteus UTI can give false positive), not sensitive; largely replaced by IFA and ELISA

---

26. ⭐⭐⭐ Microscopic Differences in Plasmodium Species

---

27. ⭐⭐⭐ Vi Antigen

• Nature: Polysaccharide capsular antigen (Vi = virulence antigen); heat-labile; located on surface of Salmonella Typhi
• Present in: S. Typhi, S. Paratyphi C, S. Dublin
• Functions:
  1. Antiphagocytic - prevents phagocytosis by macrophages
  2. Masks O antigen → blocks O antibody-mediated complement activation
  3. Contributes to intracellular survival
• Clinical significance:
  • Vi-negative strains are less virulent
  • Vi-typing (phage typing of Vi-positive strains) used for epidemiological tracking (94 phage types)
  • Fresh isolates of S. Typhi are Vi-positive → may give false negative Widal test (O agglutination blocked)
• Vaccine: Vi polysaccharide vaccine (ViPS) - 25 µg SC/IM; protects for 2-3 years; used in India
• Diagnosis of chronic carriers: Elevated anti-Vi antibody titre (>1:40) suggests chronic faecal carriage

---

28. ⭐⭐⭐ Lab Diagnosis of Neonatal HIV

Tests Used

Algorithm

1. Virological test at birth (if high-risk/exposed) → at 4-6 weeks → at 6 months
2. Two positive virological tests = definitive diagnosis of HIV infection
3. If all virological tests negative and child remains asymptomatic → antibody test at 18 months

---

29. ⭐⭐⭐⭐⭐ Germ Tube Test

• Purpose: Rapid, presumptive identification of Candida albicans
• Principle: C. albicans produces germ tubes (true hyphae without constriction) when incubated in serum at 37°C for 2-3 hours
• Procedure:
  1. Suspend a small colony of yeast in 0.5 mL human/sheep serum
  2. Incubate at 37°C for 2-3 hours (not longer → may give false positives)
  3. Place a drop on a glass slide, coverslip
  4. Examine under light microscope (10× or 40×)
• Positive result: Filamentous outgrowth (germ tube) from yeast cell without constriction at point of origin
• Interpretation: Germ tube positive = Candida albicans (or C. dubliniensis - also positive)
• Negative result: No germ tube = other Candida spp. (C. tropicalis, C. parapsilosis, C. glabrata, C. krusei)
• Significance: Simple, rapid, inexpensive; done directly from blood culture bottle or colony
• Limitations: Cannot distinguish C. albicans from C. dubliniensis; requires microscope; false positives if incubated >4 hours

---

30. Castañeda's Medium for Blood Culture

• Used for: Blood culture for Brucella species (and other fastidious organisms)
• Design (biphasic medium):
  • Solid phase: Castañeda agar slant (on side of bottle)
  • Liquid phase: Brucella broth (at bottom of bottle)
• Principle:
  • Blood inoculated into broth
  • Bottle periodically tilted → broth washes over agar surface
  • Organisms growing in broth subculture themselves automatically onto solid agar → colonies visible without opening bottle
• Advantages:
  • Reduces risk of contamination (no need to subculture manually)
  • Reduces lab-acquired brucellosis (aerosol risk)
  • Allows continuous monitoring
• Incubation: 37°C; examined weekly; held for 6 weeks before declaring negative (Brucella grows slowly)

---

31. Brill-Zinsser Disease

• Definition: Recrudescence (relapse) of epidemic typhus (Rickettsia prowazekii) occurring years to decades after the primary attack
• Mechanism: R. prowazekii remains latent in lymph nodes/macrophages after primary infection → reactivates when immunity wanes (stress, age, illness) → mild recrudescent disease
• Named after: Nathan Brill (1910, New York) and Hans Zinsser (1934, explained the mechanism)
• Features:
  • Milder than primary epidemic typhus
  • Fever, headache, rash (less prominent)
  • No louse required for transmission (endogenous reactivation)
  • Occurs in elderly immigrants from typhus-endemic areas
• Significance:
  • Patient can infect body lice → new outbreak possible → important source of epidemic typhus in louse-infested populations
  • Demonstrates long-term persistence of rickettsia in human body
• Diagnosis: Weil-Felix (OX-19 positive, lower titre); IFA (IgG predominant, distinguishes from primary - which shows IgM)
• Treatment: Single dose doxycycline (responds rapidly)

---

1. ⭐⭐⭐⭐⭐ Classification of Vibrios

Medically Important Vibrios

V. cholerae Serogroup Classification

• O1 Group → Pandemic cholera
  • Classical biotype
  • El Tor biotype
  • Each has 3 serotypes: Ogawa, Inaba, Hikojima
• O139 (Bengal) → Epidemic cholera (1992 onwards)
• Non-O1 / Non-O139 → Non-cholera vibrios (NAG - Non-Agglutinating Vibrios)

---

2. ⭐⭐⭐⭐⭐ Classical vs El Tor Biotype of V. cholerae

---

3. ⭐⭐⭐⭐⭐ String Test (Oxidase Test / Vibrio String Test)

A. String Test for Vibrio (More commonly asked in micro)

• Principle: Vibrios are susceptible to sodium deoxycholate (bile salt) → lyse in 0.5% sodium deoxycholate
• Actually, the string test for Vibrio:
  • A loopful of bacterial colony is mixed with 0.5% sodium deoxycholate on a glass slide
  • Gently rotate → if colony becomes mucoid/stringy (viscous) → "string formation" → positive = Vibrio
  • Positive result: Bacteria lyse and release DNA → forms a viscous string when loop lifted
  • Non-Vibrio organisms: no stringing
• Significance: Differentiates V. cholerae (string +ve) from other Gram-negative rods

B. String Test / Entero-Test (for intestinal parasites - see Q13)

• Different test entirely (see below)

---

4. Diagrams

a. ⭐⭐⭐⭐⭐ Egg of Hymenolepis nana (Dwarf Tapeworm)

        ___________
       /           \
      |  ___________  |
      | /           \ |   ← Outer shell (thin, smooth)
      ||   6 HOOKS   ||   ← Inner embryophore (pyriform apparatus)
      ||  (oncosphere)||  ← 3 pairs of hooks = hexacanth embryo
      || ___/___/___  ||
      | \___________/ |   ← Polar filaments (4-8) between 
      |               |     shells = PATHOGNOMONIC
       \___________/
       
    Size: 40-50 µm
    Shape: Spherical/ovoid
    Key features:
    - Double shell
    - 4-8 polar filaments between inner & outer shell
    - Hexacanth embryo (6 hooks) inside
    - No operculum

• Outer thin shell
• Inner thick embryophore with 2 polar thickenings
• Polar filaments (4-8, coiled between shells) - pathognomonic
• Oncosphere with 3 pairs of hooklets inside

---

b. ⭐⭐⭐ Entamoeba histolytica Trophozoite & Cyst

        ___________
       /  Ectoplasm  \     ← Clear, glass-like outer zone
      |  ___________  |
      | /  Endoplasm  \|   ← Granular inner zone
      ||  [NUCLEUS]   ||   ← Peripheral chromatin (ring of beads)
      ||   ○ Karyosome ||  ← Central karyosome (small, dot-like)
      ||  [RBCs] ●●●  ||  ← Ingested RBCs (PATHOGNOMONIC)
       \___________/
       
    Size: 20-40 µm (up to 60 µm)
    Key features:
    - Unidirectional motility (pseudopodium = eruptive)
    - Ingested RBCs = diagnostic
    - Peripheral chromatin = evenly distributed
    - Central karyosome

        ___________
       /             \     ← Thick cyst wall (double-layered)
      |  N₁ N₂ N₃ N₄ |   ← 4 nuclei (mature cyst)
      |               |
      |  ~~CHROMATOID~~|  ← Chromatoid bars with blunt/rounded ends
      |    BARS       |     (cigar-shaped) - IMPORTANT
      |  [GLYCOGEN]   |   ← Glycogen mass (stains brown with iodine)
       \_____________/
       
    Size: 10-20 µm
    Immature cyst: 1-2 nuclei
    Mature cyst: 4 nuclei
    Key: Chromatoid bars = blunt ends (vs E. coli = splinter ends)

---

c. ⭐⭐⭐⭐⭐ Giardia lamblia Trophozoite & Cyst

         _______
        /   |   \       ← Pear/pyriform shaped
       |  [N] [N] |     ← 2 nuclei (bilateral symmetry)
       |   _____  |     ← Sucking disc (ventral) = adhesion organ
       |  /___/   |       occupies anterior ½
       |  | | | | |     ← 4 pairs of flagella (8 flagella total)
       |  | | | | |       (2 anterior, 2 caudal, 2 ventral, 2 lateral)
       |  \___/   |     ← 2 median bodies (comma/claw-hammer shaped)
       |    ||||  |     ← Axonemes (median rods)
        \___|___/
            |
    Size: 10-20 µm × 5-7 µm
    "Face-like" appearance (owl-face / monkey face)
    Key: Sucking disc, 2 nuclei, 4 pairs flagella, median bodies

        __________
       /           \     ← Thick smooth cyst wall
      | N₁ N₂ N₃ N₄|   ← 4 nuclei (pushed to one side/pole)
      |  __________ |
      | /  Axonemes \|  ← Longitudinal axonemes (intracytoplasmic)
      | \__flagella_/|  ← Remnant flagellar structures
      |  [Median bodies]
       \__________/
       
    Size: 8-12 µm × 7-10 µm
    Shape: Oval/ellipsoid
    Key: 4 nuclei (all at one end), axonemal remnants, fibrils

---

d. ⭐⭐⭐ Egg of Trichuris trichiura & Enterobius vermicularis

        ___________
       |           |     
       @ ~~~~~~~~~ @     ← BARREL/FOOTBALL shaped
       |           |     ← Thick brown shell
       @_________@_      ← BIPOLAR PLUGS (mucoid, colorless)
                           at both ends = PATHOGNOMONIC
    
    Size: 50-55 × 22-23 µm
    Brown/yellow-brown
    Unsegmented larva inside (not embryonated when passed)
    Key: Barrel shape + 2 polar plugs

       ____________
      /    FLAT    \     ← PLANO-CONVEX (D-shaped / asymmetric)
     |   _________  |    ← One side flat, one side convex
     |  |COILED   | |   ← Coiled larva visible inside
     |  |LARVA    | |     (embryonated when passed)
     |  |_________| |
      \____________/
    
    Size: 50-60 × 20-30 µm
    Thin shell, colorless/transparent
    Key: D-shaped/asymmetric, coiled larva inside, embryonated
    Detected by: Graham's SCOTCH TAPE/CELLOPHANE TAPE method
    NOT found in routine stool (eggs deposited perianally)

---

5. ⭐⭐⭐⭐⭐ 6 Viruses Causing Diarrhoea

---

6. ⭐⭐⭐⭐⭐ NIH Swab & Its Applications

What It Is

• NIH swab (National Institutes of Health swab) = Rectal swab used for collection of specimens in acute diarrhoea, especially for Vibrio cholerae

Description

• A swab made of cotton/alginate mounted on a thin flexible wire
• Designed to reach rectum (beyond the anal sphincter) to collect material from the intestinal lumen
• Can be inserted 3-4 cm beyond the anus

Procedure

1. Patient in left lateral position
2. Insert the NIH swab gently into the rectum (~3-4 cm)
3. Rotate gently to collect material
4. Withdraw and place in Cary-Blair transport medium or VR (Venkatraman-Ramakrishnan) medium
5. Transport to lab promptly

Applications

1. Primary: Collection of rectal specimens for cholera diagnosis (V. cholerae)
2. Diagnosis of other intestinal infections: Shigella, Salmonella, Campylobacter
3. Useful when patient cannot produce stool on demand
4. Better yield than surface swab as reaches actual intestinal contents
5. Used in surveillance/field studies for cholera detection

Transport Media Used with NIH Swab

• VR (Venkatraman-Ramakrishnan) medium - for cholera
• Cary-Blair medium - general purpose for enteric pathogens
• Alkaline peptone water (APW) - enrichment for Vibrio

---

7. ⭐⭐⭐⭐⭐ Mechanism of Action of Cholera Toxin

Structure of Cholera Toxin (CT / Choleragen)

• A subunit (27 kDa): Active enzymatic component
  • A1 (21 kDa) - toxic
  • A2 (6 kDa) - linker
• B subunit (5 identical subunits, 11.5 kDa each): Binding component (pentameric ring)

Step-by-Step Mechanism

1. CT B subunit binds to GM1 ganglioside receptor
   on brush border of small intestinal epithelial cells
        ↓
2. CT A subunit enters cell via endocytosis
        ↓
3. A1 fragment activated by host cell glutaredoxin (cleaves A1 from A2)
        ↓
4. A1 = ADP-ribosyl transferase
   → Transfers ADP-ribose from NAD+ onto Gsα protein
        ↓
5. ADP-ribosylation of Gsα → PERMANENTLY ACTIVATES Gsα
   (Gsα cannot hydrolyze GTP → locked in "on" position)
        ↓
6. Persistently activated Gsα → stimulates Adenylate Cyclase
        ↓
7. ↑↑ cAMP (cyclic AMP)
        ↓
8. Activated PKA (Protein Kinase A)
        ↓
9. Phosphorylates CFTR (cystic fibrosis transmembrane conductance regulator)
   → ↑Cl⁻ secretion into lumen
   → Inhibits Na⁺/Cl⁻ absorption (inhibits NHE3 = Na-H exchanger)
        ↓
10. ↑↑ Cl⁻ in lumen → water follows osmotically
    → MASSIVE WATERY DIARRHOEA ("rice-water stools")
    → Na⁺, K⁺, HCO₃⁻ loss → dehydration, acidosis, hypokalemia

---

8. ⭐⭐⭐ Bacillus cereus Food Poisoning

---

9. ⭐⭐⭐⭐⭐ Organisms Causing Dysentery

Bacillary Dysentery (Shigellosis)

• Shigella dysenteriae (most severe, Shiga toxin)
• Shigella flexneri, S. sonnei, S. boydii
• Enteroinvasive E. coli (EIEC)
• Campylobacter jejuni (bloody diarrhoea)
• Salmonella (non-typhoidal)
• Yersinia enterocolitica

Amoebic Dysentery

• Entamoeba histolytica

Other

• Clostridium difficile (pseudomembranous colitis - bloody)
• Enterohemorrhagic E. coli (EHEC - O157:H7; bloody but no fever)
• Vibrio parahaemolyticus (inflammatory diarrhoea)
• Schistosoma mansoni/japonicum (chronic - eggs in stool)

---

10. ⭐⭐⭐ Hyperinfection Syndrome

• Organism: Strongyloides stercoralis
• Definition: Accelerated autoinfection leading to massive worm burden
• Occurs in: Immunocompromised patients (steroids, HTLV-1, haematological malignancy, transplant recipients, malnutrition)
• Mechanism: Normally filariform larvae (L3) are passed out → in hyperinfection, L3 larvae penetrate intestinal wall in large numbers and also skin → carry gut bacteria → disseminated infection
• Features:
  • Severe GI symptoms (abdominal pain, distension, paralytic ileus, GI haemorrhage)
  • Gram-negative bacteraemia/sepsis (larvae carry gut flora through intestinal wall)
  • Pulmonary: Larval migration → haemoptysis, consolidation
  • Meningitis (Gram-negative meningitis - rare)
  • Urticarial/petechial rash
• Diagnosis: Many larvae in stool, sputum, BAL, CSF
• Treatment: Ivermectin (drug of choice); Albendazole (alternative)
• Mortality: High if untreated; screen before immunosuppression in endemic areas

---

11. ⭐⭐⭐⭐⭐ Organisms Causing Traveller's Diarrhoea

• Definition: Diarrhoea occurring within 2 weeks of travel to developing countries
• Most common cause (~50-75%): Enterotoxigenic E. coli (ETEC) - produces heat-labile (LT) and heat-stable (ST) toxins

---

12. O139 Strain of Cholera

• Emerged: 1992, Madras (Chennai), India and Bangladesh → new serogroup
• Strain: Vibrio cholerae O139 Bengal
• Significance: First non-O1 strain to cause epidemic cholera (previously only O1 caused epidemics)
• Features:
  • Possesses capsule (unlike O1) → survives better in environment; more invasive
  • Produces same cholera toxin (CT) as O1 → identical clinical disease
  • El Tor-like biotype
  • Capsule provides resistance to serum bactericidal activity
  • Previously immune individuals to O1 were susceptible (no cross-immunity)
  • Initial concern it would cause 8th pandemic → did not spread globally
• Epidemiology: Remains mostly in South Asia; O1 El Tor regained dominance
• Detection: Does not agglutinate O1 antiserum; requires specific O139 antiserum

---

13. ⭐⭐⭐ Entero-Test (String Test / Enteric Capsule Test)

• Purpose: Collecting duodenal/jejunal contents for diagnosis of Giardia lamblia, Strongyloides larvae, Cryptosporidium, Cystoisospora, bile duct parasites (Clonorchis, Fasciola)
• Material: Gelatin capsule containing a coiled nylon string (weighted with a mercury sinker/tungsten)
• Procedure:
  1. Patient fasts overnight
  2. Capsule swallowed → capsule dissolves in stomach → string uncoils
  3. Patient lies on right side → peristalsis carries string into duodenum/upper jejunum
  4. Leave in place for 4 hours (or overnight)
  5. String withdrawn; bile-stained mucus adhering to distal end collected
  6. Examine microscopically for parasites/cysts/larvae
• Advantages: Non-invasive; avoids endoscopy; good sensitivity for small bowel parasites
• Disadvantages: Uncomfortable; unreliable if peristalsis poor; replaced by duodenal aspiration via endoscopy
• Applications: Giardiasis (when stool examination negative × 3); Strongyloides; Cryptosporidium; bile duct flukes

---

14. ⭐⭐⭐ Larva Currens

• Meaning: Latin = "racing/running larva"
• Organism: Strongyloides stercoralis
• Mechanism: Filariform (L3) larvae produced in intestine penetrate perianal skin during external autoinfection → migrate rapidly through dermis
• Clinical Features:
  • Rapidly migrating serpiginous (snake-like) urticarial tracks in skin
  • Located on: perianal region, buttocks, groin, lower abdomen, thighs
  • Speed of migration: 5-15 cm/hour (much faster than cutaneous larva migrans = CLM)
  • Intense pruritus
  • Lesions appear, migrate, disappear within hours → reappear
• Distinction from Cutaneous Larva Migrans (CLM):
  • CLM = hookworm (Ancylostoma) larvae from soil → slow (few cm/day); stays in feet/legs
  • Larva currens = Strongyloides larvae → fast; perianal/truncal; recurrent
• Significance: Marker of ongoing autoinfection; seen in chronic strongyloidiasis
• Treatment: Ivermectin 200 µg/kg/day × 2 days (drug of choice)

---

15. ⭐⭐⭐⭐⭐ Auto-Infection

Types in Parasitology

• Strongyloides stercoralis: rhabditiform larvae → filariform larvae in intestine → penetrate gut wall → enter circulation → complete life cycle without leaving host
• Basis of chronic strongyloidiasis (lasts decades)

• Larvae excreted in stool penetrate perianal skin → causes larva currens
• Strongyloides stercoralis: L3 larvae penetrate perianal skin → autoinfection

• Enterobius vermicularis (pinworm): eggs hatch at anal margin → larvae migrate back into rectum → develop to adults → retroinfection
• Taenia solium: eggs from own stool ingested accidentally → cysticercosis (internal autoinfection)

• Strongyloides stercoralis (main)
• Enterobius vermicularis
• Taenia solium (accidental ingestion of own eggs → cysticercosis)
• Hymenolepis nana (internal autoinfection without intermediate host)

---

16. ⭐⭐⭐ Mycotoxicoses vs Mycetism

---

17. ⭐⭐⭐⭐⭐ Taenia saginata vs Taenia solium

---

18. ⭐⭐⭐⭐⭐ Egg Groups

a. Bile-Stained Eggs (Yellow-Brown / Bile-Stained)

1. Ascaris lumbricoides (fertilized egg) - golden yellow-brown, mammillated
2. Trichuris trichiura (whipworm) - yellow-brown, barrel with polar plugs
3. Taenia spp. (T. solium, T. saginata) - brown, radially striated embryophore

b. Non-Bile-Stained Eggs (Colourless/Clear)

1. Enterobius vermicularis (pinworm) - colourless, transparent, D-shaped
2. Hookworm (Ancylostoma, Necator) - colourless, thin-shelled, unsegmented/segmented
3. Strongyloides stercoralis - colourless (larvae usually found, not eggs)
4. Hymenolepis nana - colourless outer shell
5. Fasciola hepatica - pale yellow/operculated (some classify as bile-stained)

c. Eggs that FLOAT in Saturated Salt Solution (Low specific gravity)

1. Ascaris lumbricoides (fertilized)
2. Trichuris trichiura
3. Hookworm (Ancylostoma, Necator)
4. Enterobius vermicularis
5. Hymenolepis nana
6. Taenia spp.

d. Eggs that SINK in Saturated Salt Solution (High specific gravity - do NOT float)

1. Fasciola hepatica (large operculated fluke eggs)
2. Schistosoma spp. (heavy eggs with spine)
3. Paragonimus westermani
4. Unfertilized Ascaris eggs (heavy)
5. Clonorchis/Opisthorchis (small but dense operculated eggs)
6. Diphyllobothrium latum (large operculated)

e. Soil-Transmitted Helminths (STH)

1. Ascaris lumbricoides (roundworm) - most common STH
2. Trichuris trichiura (whipworm)
3. Ancylostoma duodenale (hookworm)
4. Necator americanus (hookworm)
5. Strongyloides stercoralis (threadworm)
6. (Enterobius vermicularis - some include; technically does not require soil)