Leishmania Species
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Direct answer
Kala-azar, the black fever of the Gangetic plains, is visceral leishmaniasis from Leishmania donovani, transmitted in the Indian subcontinent by the sandfly Phlebotomus argentipes in an anthroponotic cycle where humans alone carry the parasite. The diagnostic unit is the amastigote — the Leishman-Donovan body, 2-5 micrometres, a nucleus beside a rod-shaped kinetoplast visible as a dot-and-dash pair inside macrophages of spleen, bone marrow and liver. Illness is prolonged fever with massive splenomegaly, pancytopenia, hypergammaglobulinaemia and skin darkening; post-kala-azar dermal leishmaniasis follows treatment. India's programme response pairs the rK39 rapid test with single-infusion liposomal amphotericin B under the kala-azar elimination initiative targeting less than one case per 10,000 population annually at block level across Bihar, Jharkhand, West Bengal and Uttar Pradesh.
What you must remember
- Species map: L. donovani complex (visceral; anthroponotic in India, L. infantum/chagasi zoonotic elsewhere), L. tropica and L. major (Old World cutaneous), L. braziliensis (New World mucocutaneous espundia) and L. mexicana; vectors are Phlebotomus (Old World) and Lutzomya (New World) sandflies.
- Morphology: promastigote — flagellated, extracellular, the form in the sandfly and on NNN (Novy-MacNeal-Nicolle) culture; amastigote — round-to-oval LD body with nucleus and kinetoplast, the form in macrophages of the reticuloendothelial system.
- Clinical visceral disease: weeks-to-months fever with classically double-quotidian spikes, spleen enlarging faster than liver, pancytopenia with bleeding and infections, hypergammaglobulinaemia (positive formol gel and aldehyde tests), hypoalbuminaemia, and hyperpigmentation of temples and hands giving kala-azar its name.
- PKDL: macular, papular or nodular hypopigmented rash appearing months to years after cure — non-febrile but parasitologically alive, and the reservoir that sustains anthroponotic transmission.
- Diagnosis: rK39 immunochromatographic strip — the field cornerstone of the Indian programme; direct agglutination test in reference centres; demonstration of LD bodies in splenic aspirate (most sensitive), bone marrow or lymph node; NNN culture and PCR or CBNAAT amplification where available.
- Treatment: national first-line is single-infusion liposomal amphotericin B 10 mg/kg; alternatives — miltefosine (oral, teratogenic, resistance-tempered), paromomycin, and combination short courses.
- Elimination framework: NVBDCP's programme defines elimination as annual incidence below 1 case per 10,000 population at block primary health centre level, pursued through rK39-based early detection, treatment, indoor residual spraying and active PKDL hunt.
- Differential discipline: fever with splenomegaly and pancytopenia in an endemic district must outrank chronic malaria, enteric fever, lymphoma and hypersplenism before being labelled anything else.
A fever with a huge spleen, worked through
A 22-year-old from Bihar's Vaishali district has six weeks of evening fever, weight loss and a spleen ten centimetres below the costal margin; haemoglobin 6 g/dL, white cells 2,400, platelets 60,000. Malaria and dengue are negative; the rK39 strip turns positive within twenty minutes. A splenic aspirate under platelet-cover discipline remains the reference standard — its parasite burden (LD bodies per field) exceeding even rK39 sensitivity — though the programme pathway treats most cases on rK39 alone, with bone marrow where splenic aspiration is judged too risky.
Treatment is the single-day liposomal amphotericin B infusion — modern advantage over month-long stibogluconate courses that Indian parasites resist. Defervescence within the week, a shrinking spleen over months and a haematological climb confirm cure. Counselling closes the loop: any skin patch over the next two years matters, because post-kala-azar dermal leishmaniasis — hypopigmented macules on face and trunk — is both relapse risk and the village's reservoir, which is why programme workers photograph skin at follow-up. The elimination arithmetic belongs in every answer: sustained incidence below 1 per 10,000 at block level, pursued through indoor residual spraying, case hunts and PKDL detection across the four endemic states.
High-yield viva angles
The kinetoplast question arrives early: differentiate the intracellular LD body from Histoplasma (nucleus plus kinetoplast dot-and-dash versus a single nucleus), and name the stained slide accordingly. The diagnostic hierarchy earns marks — splenic aspirate most sensitive, bone marrow safer, rK39 the programme's rapid test, the aldehyde (formol gel) test the historic globulin-based relic still asked for its name. The vector's second job earns a viva nod: Phlebotomus also transmits Bartonella bacilliformis (Oroya fever). The miltefosine story is quotable national history — the first oral antileishmanial, born of Indian research, tempered by teratogenicity and resistance. Finally, PKDL's role as inter-epidemic reservoir turns a dermatology footnote into the key to elimination strategy.
Frequently asked questions
What is an LD body?
The Leishman-Donovan body — the 2-5 micrometre amastigote inside macrophages, showing a nucleus and rod-shaped kinetoplast (the dot-and-dash pair) on Giemsa.
Which sandfly transmits kala-azar in India?
Phlebotomus argentipes, transmitting Leishmania donovani in a human-to-human (anthroponotic) cycle without an animal reservoir.
What is the rK39 test?
A rapid immunochromatographic strip detecting antibodies to a recombinant 39-kilodalton antigen, the field diagnostic backbone of India's kala-azar elimination programme.
What is the elimination target of the national programme?
Annual incidence below one case per 10,000 population at block primary health centre level, pursued through early detection, treatment, indoor residual spraying and PKDL surveillance.
What is post-kala-azar dermal leishmaniasis?
A post-treatment syndrome of hypopigmented macules, papules or nodules months to years after visceral disease — afebrile, parasitologically positive, the human reservoir sustaining transmission.