Visceral Leishmaniasis (Kala-Azar)

Visceral leishmaniasis (VL), classically called kala-azar ("black fever"), is a chronic systemic protozoal infection caused by the Leishmania donovani complex and transmitted by the female Phlebotomus sandfly. It is the second-deadliest parasitic disease after malaria and a recurring NEET PG favourite for its vector–parasite pairings, the LD-body diagnostics, and the shift to liposomal amphotericin B as first-line therapy in India.

Definition & Core Concept

Leishmaniasis is a spectrum of diseases produced by the obligate intracellular protozoan Leishmania. The clinical form depends on the species and host immunity:

• Visceral (kala-azar) — reticulo-endothelial system (spleen, liver, marrow, lymph nodes); caused by L. donovani complex.
• Cutaneous (oriental sore) — skin ulcers; L. tropica, L. major, L. mexicana.
• Mucocutaneous (espundia) — destructive naso-oropharyngeal lesions; L. braziliensis.

Visceral disease results when amastigotes parasitise macrophages of the reticulo-endothelial system, producing the hallmark triad of massive splenomegaly, pancytopenia and chronic fever. Untreated symptomatic VL is >90% fatal.

High-yield: Kala-azar = "black fever/black sickness" — refers to the greyish-black darkening of skin (face, hands, feet, abdomen) from melanocyte-stimulating effects. Kala = black, azar = fever/disease (Hindi/Assamese).

Aetiology — The L. donovani Complex

Species	Geography	Reservoir	Notes
L. donovani	India, Bangladesh, Nepal, East Africa	Anthroponotic (man-to-man)	Causes Indian kala-azar; PKDL common
L. infantum	Mediterranean, Middle East, Central Asia	Zoonotic (dogs)	Infantile VL
L. chagasi	South America	Zoonotic (dogs, foxes)	= L. infantum genetically

High-yield: In the Indian subcontinent VL is anthroponotic — humans are the only reservoir, so there is no animal reservoir to control. This makes VL theoretically eradicable, and underpins the WHO/India Kala-Azar Elimination Programme (target <1 case per 10,000 at block level).

The Vector

• Vector: female sandfly — Phlebotomus argentipes (Indian subcontinent); Lutzomyia in the New World.
• Sandflies are small, hairy, "hopping" fliers; breed in cracked mud walls, cattle sheds; bite at dusk/night.
• Transmission is by bite of the infected female sandfly; rarely by blood transfusion, congenital, sharing needles (IVDU + HIV).

Life cycle (flow): Sandfly bites human → injects promastigotes (flagellated, infective) → engulfed by macrophages → transform into amastigotes (aflagellate, LD bodies) → multiply by binary fission, rupture macrophage → spread through RES → another sandfly takes a blood meal, ingests amastigotes → reconvert to promastigotes in the gut/midgut → migrate to proboscis → bite next host.

Mnemonic — "Promastigote in Phlebotomus, Amastigote in Animal/man" (both Ps together; the amastigote is the human tissue form = LD body).

Pathophysiology

Amastigotes survive inside macrophage phagolysosomes by inhibiting the respiratory burst. Disease expression is determined by the Th1 vs Th2 balance:

• Th1 response (IFN-γ, IL-2) → macrophage activation, NO-mediated killing → subclinical/self-limiting infection.
• Th2 response (IL-4, IL-10, IL-13) → deactivated macrophages → uncontrolled parasite multiplication → progressive visceral disease.

Marked polyclonal B-cell activation produces hypergammaglobulinaemia (chiefly IgG) with relatively little protective value — this is the basis of the older non-specific serum tests (aldehyde test). Splenic and marrow infiltration → hypersplenism + marrow crowding → pancytopenia.

High-yield: Pancytopenia in VL is dual — hypersplenism (sequestration) plus marrow infiltration by parasitised macrophages. Reversal of albumin:globulin ratio (↑↑ globulin) is characteristic.

Clinical Features

The incubation period is typically 2–6 months (range weeks to years). Classic symptomatic disease:

1. Fever — insidious, prolonged; classically double quotidian (two spikes/day), though often irregular; patient looks remarkably well despite high fever ("fever with preserved well-being" early).
2. Splenomegaly — the dominant sign; massive, firm, non-tender, grows progressively. VL is a leading cause of massive splenomegaly in the tropics.
3. Hepatomegaly — softer, less marked than spleen.
4. Lymphadenopathy — common in African/Sudanese VL, less so in India.
5. Pancytopenia — anaemia (pallor), thrombocytopenia (bleeding/epistaxis), leucopenia (intercurrent infections).
6. Skin darkening — greyish hyperpigmentation → "kala-azar".
7. Wasting & cachexia, abdominal distension, growth retardation in children.

High-yield: A patient from Bihar/Jharkhand/West Bengal/eastern UP with prolonged fever, massive splenomegaly, pancytopenia, hyperpigmentation and hypergammaglobulinaemia = kala-azar until proven otherwise. India contributes the bulk of the disease burden (Gangetic plain).

Differentials for Massive (huge) Splenomegaly in the Tropics

• Chronic myeloid leukaemia (CML)
• Myelofibrosis
• Visceral leishmaniasis (kala-azar)
• Tropical splenomegaly syndrome / hyperreactive malarial splenomegaly (HMS)
• Thalassaemia major, Gaucher disease

High-yield: Tropical Splenomegaly Syndrome (TSS) = Hyperreactive Malarial Splenomegaly (HMS) — a separate entity from kala-azar but a common confounder. It is an aberrant immunological response to chronic/recurrent malaria (not active parasitaemia). Features: massive splenomegaly, very high serum IgM, high anti-malarial antibody titres, hepatic sinusoidal lymphocytosis, no parasites usually demonstrable, responds to prolonged antimalarial prophylaxis (not splenectomy). Distinguish from VL by demonstrating LD bodies (absent in TSS) and the IgM (vs IgG-predominant in VL).

Diagnosis & Investigation of Choice

Step-wise diagnostic approach

Clinical suspicion (endemic area + fever + massive spleen + pancytopenia) → rk39 rapid serology (screening) → tissue demonstration of LD bodies (confirmatory) → splenic aspirate has highest yield; bone marrow safest.

A. Demonstration of the parasite (gold standard)

LD bodies (Leishman–Donovan amastigotes) are sought in Giemsa-stained aspirates — small (2–4 µm) oval bodies with a nucleus and a rod-shaped kinetoplast, lying inside macrophages.

Specimen	Sensitivity	Comment
Splenic aspirate	~95% (highest)	Most sensitive but risk of bleeding/rupture; needs platelets >40,000 & normal PT
Bone marrow aspirate	60–85%	Safest commonly used confirmatory test
Lymph node aspirate	50–65%	Useful in African VL
Liver biopsy	variable	Rarely needed

• NNN medium (Novy–MacNeal–Nicolle) — culture medium; aspirate grows promastigotes.
• PCR — most sensitive molecular tool; used for diagnosis, HIV co-infection, treatment monitoring and species ID.

High-yield: Splenic aspirate = highest sensitivity for LD bodies; bone marrow aspirate = safest routinely chosen test. NNN medium grows the promastigote form.

B. Serology / antigen tests

• rk39 immunochromatographic strip test — recombinant kinesin antigen; rapid, point-of-care, first-line screening in India (high sensitivity & specificity for Indian L. donovani). Limitation: stays positive for years after cure, so cannot assess relapse/response.
• Direct agglutination test (DAT) — sensitive, used in field surveys.
• Aldehyde test of Napier (formol-gel test) — historical/non-specific: a drop of formalin added to the patient's serum turns it opaque white "like the white of a boiled egg" and jelly-like within minutes, owing to massive hypergammaglobulinaemia (IgG). Becomes positive only after ~3 months; not diagnostic (positive in any hypergammaglobulinaemic state). Classic eponymous NEET fact.

High-yield: Napier's aldehyde test detects raised serum globulin (IgG), NOT the parasite → it is non-specific and merely supportive. rk39 is the practical first-line; antimony-specific antibody / leishmanin (Montenegro) skin test is NEGATIVE during active VL and becomes positive only after cure (delayed-type hypersensitivity returns once cell-mediated immunity recovers).

C. Supportive labs

• CBC: pancytopenia; ESR very high.
• Reversed albumin:globulin ratio with polyclonal hypergammaglobulinaemia.
• Liver enzymes mildly deranged.

Management — Drug of Choice

First-line in India

High-yield: Liposomal amphotericin B (L-AmB) is the drug of choice / first-line for VL in the Indian subcontinent (WHO & national programme). A single dose of 10 mg/kg is the recommended regimen for primary VL in India — high cure rates, short course, ideal for elimination. India largely abandoned pentavalent antimonials because of widespread antimony resistance in Bihar.

Drug	Route	Key points
Liposomal amphotericin B	IV	First-line in India; single high dose; minimal nephrotoxicity vs deoxycholate; costly
Miltefosine	Oral	First oral anti-VL drug; teratogenic (contraindicated in pregnancy, contraception needed); GI upset; resistance emerging
Paromomycin (aminosidine)	IM	Aminoglycoside; cheap; ototoxicity
Pentavalent antimonials (sodium stibogluconate, meglumine antimoniate)	IV/IM	Historical first-line; high resistance in Bihar; cardiotoxic (QT), pancreatitis
Amphotericin B deoxycholate	IV	Effective but nephrotoxic, infusion reactions

• Combination therapy (e.g., single-dose L-AmB plus short oral miltefosine, or L-AmB plus paromomycin) is increasingly used to shorten total treatment duration, improve adherence and limit emergence of drug resistance, all of which serve the elimination agenda.
• General measures: treat anaemia (transfusion), correct hypoalbuminaemia and nutrition, manage intercurrent infections aggressively, and screen for HIV co-infection. Vector control (indoor residual spraying for sandflies, bed nets) and early case detection/treatment of VL and PKDL are the public-health pillars; there is currently no licensed human vaccine.
• HIV–VL co-infection: poorer response, frequent relapse; L-AmB preferred + secondary prophylaxis + antiretroviral therapy.

Marker of cure: clinical (defervescence, spleen regression, weight gain) — parasitological cure cannot rely on rk39 (stays positive).

Post-Kala-Azar Dermal Leishmaniasis (PKDL)

A dermatosis appearing months to years after apparent cure of VL (or sometimes without prior overt VL), almost exclusively with L. donovani.

• India: appears 6 months – 3+ years after treatment; lesions are macules → papules → nodules, typically symmetrical, starting on the face (peri-oral, "butterfly" malar distribution) spreading to trunk and limbs.
• Sudan/Africa: appears earlier (within months), often with a maculopapular/measles-like rash, may self-heal.

High-yield: PKDL patients act as a human reservoir for L. donovani between epidemics — the lesions teem with parasites and sustain transmission in an anthroponotic cycle. Treating PKDL is essential to the kala-azar elimination programme. PKDL must be differentiated from leprosy (lesions of PKDL retain sensation and sweating — they are not anaesthetic, unlike leprosy).

Complications

• Secondary infections — pneumonia, tuberculosis, dysentery, measles, cancrum oris and bacterial sepsis (driven by leucopenia and impaired cell-mediated immunity) — these intercurrent infections are the usual cause of death in untreated kala-azar rather than the parasitaemia itself.
• Bleeding — thrombocytopenia → epistaxis, gum/GI bleeds.
• Severe anaemia, cachexia, hypoalbuminaemia, oedema.
• Noma / cancrum oris, amphotericin-related nephrotoxicity and hypokalaemia from therapy.
• PKDL (a sequel/complication of treated VL).
• Immune reconstitution and relapse in HIV co-infection.

Key Differentials

Feature	Kala-azar (VL)	Malaria / HMS (TSS)	CML	Enteric (typhoid)
Fever pattern	Insidious, ± double quotidian	Periodic (tertian/quartan) / chronic	Low-grade	Step-ladder, rising
Spleen	Massive, firm	Massive (HMS)	Massive	Mild/moderate
Blood film	LD bodies in marrow	Ring forms (acute malaria)	↑ Neutrophils + precursors, low LAP	Usually normal
Diagnostic clue	rk39+, LD bodies, ↑IgG	Smear/RDT; HMS ↑↑IgM	t(9;22) BCR-ABL	Blood/stool culture, Widal
WBC	Leucopenia	Variable	Marked leucocytosis	Leucopenia

Recently asked / exam angle

• Vector–parasite pairing: Phlebotomus (argentipes) sandfly transmits L. donovani — frequently asked one-liner.
• LD bodies = amastigote form, found intracellularly in macrophages; the kinetoplast is the identifying feature on Giemsa stain.
• Most sensitive vs safest test: splenic aspirate (most sensitive) vs bone marrow (safest) — classic two-option MCQ.
• NNN medium grows promastigotes — image/identification question.
• Aldehyde (Napier) test reflects hypergammaglobulinaemia, not the parasite — recurrent trap.
• Leishmanin (Montenegro) test is negative in active VL, positive after cure — tests cell-mediated immunity.
• Drug of choice in India = liposomal amphotericin B, single dose; miltefosine = first oral drug, teratogenic.
• PKDL as the human reservoir maintaining transmission; differentiate from leprosy by preserved sensation.
• VL in the Indian subcontinent is anthroponotic (no animal reservoir) — basis of elimination.
• HIV co-infection → atypical presentation, relapse, secondary prophylaxis.

Rapid revision

1. Kala-azar = visceral leishmaniasis = L. donovani complex; "black fever" from skin hyperpigmentation.
2. Vector = female sandfly Phlebotomus argentipes (India); bites at dusk.
3. Infective form injected = promastigote; human tissue form = amastigote (LD body) inside macrophages.
4. Indian VL is anthroponotic — man is the sole reservoir → eradicable.
5. Triad: prolonged fever (± double quotidian) + massive splenomegaly + pancytopenia, with hyperpigmentation and wasting.
6. Hypergammaglobulinaemia (IgG) with reversed A:G ratio is characteristic.
7. Splenic aspirate = most sensitive for LD bodies; bone marrow = safest test.
8. NNN medium cultures the promastigote; PCR most sensitive molecularly.
9. rk39 strip = first-line screening (stays positive after cure); aldehyde test of Napier = non-specific globulin test.
10. Leishmanin/Montenegro skin test negative in active disease, positive after cure.
11. Liposomal amphotericin B (single 10 mg/kg) = drug of choice in India; miltefosine = first oral drug, teratogenic; antimony resistance rampant in Bihar.
12. PKDL appears months–years post-cure, mimics leprosy (but sensation preserved) and sustains transmission as a human reservoir.