🔬 MI 3.7 - Kala-azar (Visceral Leishmaniasis)

Note: Apurba Sastry's book is not in the digital library, but the content below is based on Murray's Medical Microbiology 9e, Jawetz Microbiology 28e, and Harrison's 22e - which cover the same MBBS competency topics. The concepts align with Apurba Sastry's syllabus framework.

🧠 CONCEPT FIRST: What Is Leishmania donovani?

🦟 THE ORGANISM - Morphology

Dono forms yaad karo - "PAM" mnemonic:

P - Promastigote (sandfly mein / culture mein)
A - Amastigote (human macrophage mein)
M - Macro size difference

🎯 Key Point: LD Bodies

• Amastigotes = LD bodies (Leishman-Donovan bodies)
• Nucleus = "dot", Kinetoplast = "dash" → "dot-dash" appearance
• Found intracellularly in macrophages of spleen, liver, bone marrow, lymph nodes

🔄 LIFE CYCLE - Flowchart

SAND FLY BITES HUMAN
        ↓
Promastigotes deposited in skin
        ↓
Phagocytosed by skin macrophages
        ↓
Transform into AMASTIGOTES (LD bodies)
        ↓
Multiply inside macrophage → Cell bursts
        ↓
Released amastigotes → phagocytosed by new macrophages
        ↓
Spread via RES: Spleen → Liver → Bone Marrow → Lymph nodes
        ↓
        ↕ [When sandfly bites infected human]
Sandfly ingests amastigotes in blood meal
        ↓
In sandfly gut: Amastigotes → Promastigotes (flagellated)
        ↓
Promastigotes multiply → migrate to proboscis
        ↓
Ready to infect next human (INFECTIVE STAGE = Promastigote)

🦟 Vector: Phlebotomus argentipes (India/South Asia)

• Only female sand fly bites (for blood meal)
• Bites at dusk/dawn (crepuscular)
• Cannot fly in wind >1 m/s (small, fragile)

🌍 EPIDEMIOLOGY

• B - Bangladesh
• I - India (Bihar highest)
• N - Nepal
• S - Sudan

• India: Humans only (anthroponotic) → so vector control + treatment = elimination possible
• Mediterranean/Americas: Dogs, foxes, jackals (zoonotic, L. infantum) → harder to eliminate

⚡ PATHOGENESIS

L. donovani enters macrophage
          ↓
Survives phagolysis by:
- Inhibiting respiratory burst
- Preventing phagolysosome fusion
- Scavenging ROS
          ↓
   ┌──────────────────────────┐
   ↓                          ↓
Strong Th1 response      Weak/Th2 response
(IL-12, IFN-γ, TNF)      (IL-4, IL-10)
   ↓                          ↓
Macrophage activation     Impaired killing
Parasite killed           Parasite multiplies
ASYMPTOMATIC              KALA-AZAR disease
(Positive leishmanin      (Negative leishmanin
skin test = immunity)     skin test = anergy)

• Spleen enlarges massively → hypersplenism → destroys all blood cells
• Bone marrow infiltrated by parasites → decreased production
• Autoantibodies form (hypergammaglobulinemia) → hemolysis

🩺 CLINICAL FEATURES

• Pancytopenia (leukopenia + anemia + thrombocytopenia)
• Elevated ESR
• Hypoalbuminemia
• Hypergammaglobulinemia (polyclonal IgG rise) → reversal of A:G ratio
• Elevated liver enzymes

• Occurs months-years after treatment in India (20-30%) and Sudan (50%)
• Macular/papular/nodular skin lesions (hypopigmented or erythematous)
• Patient remains reservoir for sandfly transmission - important for elimination!

🔬 DIAGNOSIS - Complete Flowchart

SUSPECTED KALA-AZAR
(Fever + Splenomegaly + from endemic area)
              ↓
    ┌─────────────────────┐
    ↓                     ↓
SEROLOGICAL             PARASITOLOGICAL
(Non-invasive)          (Gold Standard)
    ↓                     ↓
rK39 RDT ←─ FIELD       Splenic aspirate (>95% sensitivity)
(best for               Bone marrow biopsy (60-85%)
 field/endemic)         Lymph node aspirate (50%)
    ↓                     ↓
ELISA / IFAT ←─ LAB    Giemsa stain → LD bodies seen
    ↓                     ↓
    └────────► PCR / LAMP (Most sensitive, species ID)
              (Gold standard for research/confirmation)
              
    Also: Aldehyde test (Chopra's test) - historical
          Formol-gel test - hypergammaglobulinemia proxy

🎯 Key Points on Diagnosis:

• Negative in active kala-azar (patient is anergic = Th2 predominance)
• Becomes positive after successful treatment (immunity restored)
• Used for epidemiological surveys, not active disease diagnosis

💊 TREATMENT

INDIA (Bihar - antimonial resistant):
First line: Liposomal Amphotericin B (LAMB)
         OR Miltefosine (oral, first oral drug for VL!)
         OR Conventional AmB deoxycholate

REST OF WORLD:
First line: Pentavalent Antimonials (SbV)
- Sodium stibogluconate (Pentostam): 20 mg/kg/day x 28-30 days
- Meglumine antimoniate (Glucantime): same dose
→ Resistance widespread in Bihar → NOT used there

🔑 MNEMONICS SUMMARY FOR KALA-AZAR

"BINS" = Bangladesh, India, Nepal, Sudan (90% burden)
"DOT-DASH" = LD body (nucleus=dot, kinetoplast=dash)
"SAFE + dark" = Splenomegaly, Anemia, Fever, Emaciation + dark skin
"LAMB First in India" = Liposomal AmB preferred in Bihar
"Sandfly = Phlebotomus" (P for P for Phlebotomus = Promastigote deposited)
"PKDL = Persistent Kala-azar Dermal Lesion" (source of infection post-treatment)

🪱 MI 3.8 - Filariasis: Wuchereria bancrofti

🧠 CONCEPT FIRST: What Is Filariasis?

🦠 THE ORGANISM - Classification

Kingdom: Animalia
Phylum: Nematoda (roundworms)
Class: Secernentea
Order: Spirurida
Family: Onchocercidae
Genus: Wuchereria
Species: bancrofti

KEY FACT: W. bancrofti harbors bacterial endosymbionts
          → WOLBACHIA spp. inside worm
          → Wolbachia is essential for worm's
             metabolism, fertility & survival
          → Target for antibiotic therapy (doxycycline)!

📏 MORPHOLOGY

• W. bancrofti sheath: does NOT stain with Giemsa (pale/unstained)
• B. malayi sheath: stains bright pink with Giemsa
• This helps differentiate species in blood smear!

🔄 LIFE CYCLE - COMPLETE FLOWCHART

═══════════ IN MOSQUITO (Definitive host) ═══════════

Mosquito bites infected human
        ↓
Ingests MICROFILARIAE (L1 - diagnostic stage for human)
        ↓
Microfilariae lose sheath → penetrate stomach wall
        ↓
Migrate to THORACIC MUSCLES → L1 → L2 (sausage stage)
        ↓
L2 → L3 (infective/filariform larva)
        ↓
Migrate to HEAD & PROBOSCIS → ready to infect
        ↓ (mosquito bites next human)

═══════════ IN HUMAN (Intermediate host) ═══════════

L3 larvae deposited near bite wound (NOT injected)
        ↓
Penetrate skin → enter lymphatics
        ↓
Migrate to LYMPHATIC VESSELS (arms, legs, groin, scrotum)
        ↓
L3 → L4 → Adult worms (takes 3-12 months)
        ↓
♂ fertilizes ♀ → ♀ produces MICROFILARIAE
        ↓
Microfilariae enter BLOOD CIRCULATION
(NOCTURNAL PERIODICITY - peak at night, 10pm-4am)
        ↓
Ready to be ingested by next feeding mosquito

🦟 Vectors (Mosquito species):

• C - Culex (most important in India: Culex quinquefasciatus)
• A - Aedes
• A - Anopheles

Key: In India, Culex quinquefasciatus is the principal vector

⏰ NOCTURNAL PERIODICITY - Why Important?

Normal form: Microfilariae in PERIPHERAL blood at NIGHT
             (10 PM - 4 AM)
             During day → sequestered in PULMONARY capillaries

Why? Synchronized with mosquito biting habits
     (Culex bites at night)

Subperiodic form: Pacific islands (Wuchereria bancrofti var. pacifica)
                  Microfilariae always present (no strict periodicity)
                  
PRACTICAL IMPLICATION:
Blood sample for microfilaria MUST be taken at NIGHT!

💥 PATHOGENESIS & CLINICAL FEATURES

L - Latent (asymptomatic microfilaremia)
E - Early/Acute (fever, lymphangitis, lymphadenitis)  
A - Advancing (lymph node enlargement, orchitis, hydrocele)
F - Final/Chronic (elephantiasis, chyluria)

Stage 1: ASYMPTOMATIC

• Microfilariae in blood but NO symptoms
• Most common outcome in endemic areas

Stage 2: ACUTE (Lymphangitis/Adenolymphangitis = ADL)

• Fever + chills - recurring attacks
• Lymphangitis (red streaks along lymphatics)
• Lymphadenitis (tender, enlarged lymph nodes)
• Retrograde lymphangitis (from nodes outward) - distinguishes from bacterial
• Orchitis, epididymitis, funiculitis (scrotal involvement common)
• Caused by: inflammatory response to dying adult worms

Stage 3: CHRONIC (Obstructive)

• Lymphedema → Elephantiasis
  • Lower limbs (most common), scrotum, vulva, breast, arm
  • Skin becomes thick, fissured, warty
• Hydrocele (commonest manifestation overall)
• Chyluria (milky urine - lymph in urine due to lymphatic-urinary fistula)

Stage 4: TROPICAL PULMONARY EOSINOPHILIA (TPE)

• Hyperimmune response to microfilariae trapped in lungs
• Features: Paroxysmal nocturnal cough + wheeze + high eosinophilia (>3000/μL)
• Antifilarial antibodies very high
• Microfilariae ABSENT from blood (trapped in lung)
• CXR: diffuse miliary shadows or interstitial infiltrates (lower lobes)
• Responds rapidly to DEC → dramatic improvement = supports diagnosis

🔬 DIAGNOSIS - Flowchart

CLINICAL SUSPICION
(Lymphedema/Elephantiasis + endemic area)
              ↓
   ┌──────────────────────────────────┐
   ↓                                  ↓
DIRECT (Parasitological)          INDIRECT
   ↓                                  ↓
Night blood smear (10PM-4AM)      Serology:
  ↓                               - Antifilarial antibodies
  Giemsa stain                    - Circulating antigen test
  → Microfilariae seen               (for W. bancrofti, 96-100% sens)
  (sheathed, nuclei don't          - NOT for Brugia
   reach tail tip)                   
  ↓                               Eosinophilia (blood count)
Thick smear preferred             
  ↓                               Imaging:
Membrane filtration technique     - USG of scrotal lymphatics:
(concentration, ↑sensitivity)       "filarial dance sign" = live
                                     adult worms moving in dilated
Buffy coat method                    lymphatics (PATHOGNOMONIC)
  ↓                               
PCR / NAAT (most sensitive)       DEC provocative test (rarely used)

🎯 Key Diagnostic Points:

💊 TREATMENT

Drug of Choice: DIETHYLCARBAMAZINE (DEC)
- Kills microfilariae primarily
- Also kills adult worms (partial)
- Dose: 6 mg/kg/day in divided doses x 12 days
- Side effects: Mazzotti reaction (fever, rash, lymphadenitis)
               due to dying parasite antigens

COMBINATION THERAPY (Mass Drug Administration - MDA):
  DEC + Albendazole (standard MDA)
  OR
  Ivermectin + Albendazole (where onchocerciasis co-exists)

DOXYCYCLINE:
- Targets WOLBACHIA endosymbiont inside worm
- Kills adult worms (macrofilaricidal)
- 200 mg/day x 6-8 weeks
- Novel approach: "targeting the worm's bacteria"

FOR CHRONIC DISEASE:
- Lymphedema: elevation, elastic bandage, hygiene, physiotherapy
- Hydrocele: surgical correction
- Chyluria: dietary fat restriction, surgery if persistent
- Elephantiasis: irreversible (treatment of little benefit)

🔑 COMPLETE SUMMARY MNEMONICS

FILARIASIS MNEMONICS:

"WBLC" = Wuchereria Bancrofti: Lymphatic; Culex vector
"Night Blood" = take blood sample at NIGHT for microfilaria
"LEAF" = Latent → Early acute → Advanced → Final chronic
"No Nuclei in Tail Tip" = W. bancrofti microfilaria (vs Brugia)
"Sheath" = both W. bancrofti AND B. malayi are sheathed
"DEC is KEY" = Drug of choice
"WOLBACHIA = Target for Doxycycline"
"Filarial Dance Sign" = USG finding = pathognomonic
"TPE = Trapped Pulmonary Eosinophilia" = hyperimmune form

📊 COMPARISON TABLE: W. bancrofti vs B. malayi

🗂️ INTEGRATED FLOWCHART: Both Topics Side-by-Side

PARASITIC DISEASE
       ↓
┌──────────────────────┬─────────────────────────┐
│    KALA-AZAR         │      FILARIASIS          │
│  (L. donovani)       │   (W. bancrofti)         │
├──────────────────────┼─────────────────────────┤
│ Vector: Sand fly     │ Vector: Culex mosquito   │
│ (Phlebotomus)        │ (quinquefasciatus)       │
├──────────────────────┼─────────────────────────┤
│ Site: Macrophages    │ Site: Lymphatics         │
│ (intracellular)      │ (extracellular)          │
├──────────────────────┼─────────────────────────┤
│ Diagnostic form:     │ Diagnostic form:         │
│ LD body (amastigote) │ Microfilaria in blood    │
├──────────────────────┼─────────────────────────┤
│ Gold std diagnosis:  │ Gold std diagnosis:      │
│ Splenic aspirate     │ Night blood smear        │
│ rK39 RDT (field)     │ Circulating Ag test      │
├──────────────────────┼─────────────────────────┤
│ DOC in India:        │ DOC:                     │
│ Liposomal AmB /      │ DEC (Diethylcarba-       │
│ Miltefosine          │ mazine)                  │
├──────────────────────┼─────────────────────────┤
│ Hallmark features:   │ Hallmark features:       │
│ Huge splenomegaly    │ Elephantiasis            │
│ Pancytopenia         │ Nocturnal microfilaremia │
│ Dark skin            │ Hydrocele                │
└──────────────────────┴─────────────────────────┘

⭐ EXAM HIGH-YIELD POINTS (Apurba Sastry Style)

1. LD body = amastigote = "dot-dash" appearance = INTRACELLULAR in macrophage
2. Vector = Phlebotomus argentipes in India; only in South Asia = anthroponotic
3. Leishmanin test NEGATIVE in active disease, POSITIVE after cure
4. rK39 RDT = field gold standard (98% sensitivity outside East Africa)
5. PKDL = dangerous because treated patient becomes reservoir again
6. DOC in India/Bihar = Liposomal AmB (due to antimonial resistance)
7. Miltefosine = ONLY oral drug for VL; teratogenic

1. Blood sample MUST be at night (10PM-4AM) for microfilaria detection
2. Sheath present in W. bancrofti + B. malayi (mnemonic: W+B = "WITH" sheath)
3. W. bancrofti: NO nuclei reach tail tip (B. malayi: 2 discrete nuclei in tail tip)
4. "Filarial dance sign" on USG = pathognomonic = live adult worms
5. TPE = trapped microfilariae in lungs = eosinophilia + nocturnal cough + no microfilariae in blood
6. Wolbachia inside worm → target for DOXYCYCLINE (macrofilaricidal)
7. DEC = DOC for microfilariae; combination with albendazole ± ivermectin in MDA
8. India's NDA (National Filariasis Control Programme) uses annual MDA