Question
Kala azar
Answer
Kala-azar (visceral leishmaniasis) is a severe, potentially fatal systemic parasitic disease caused by Leishmania donovani (in the Indian subcontinent/East Africa; L. infantum/L. chagasi in other regions), transmitted by the bite of infected female sandflies (Phlebotomus species in the Old World).
Pathogenesis: sandfly saliva introduces infective promastigotes into the skin, which are phagocytosed by macrophages and transform into the intracellular amastigote form, surviving and multiplying within macrophages (a facultative intracellular pathogen); the parasite then disseminates via the bloodstream to the reticuloendothelial system — bone marrow, spleen, and liver — causing progressive organ enlargement and marrow suppression.
Clinical features: prolonged, often intermittent/irregular fever (classically described as having a double-rise pattern in some texts), progressive and often massive hepatosplenomegaly (splenomegaly typically more prominent), weight loss/wasting, pancytopenia (anaemia, leukopenia, thrombocytopenia — from marrow suppression and hypersplenism), and hyperpigmentation of the skin (the literal meaning of “kala-azar” is “black fever” in Hindi/Urdu, referring to this darkening, particularly of the face/hands/feet/abdomen).
Laboratory diagnosis:
- Demonstration of amastigotes (LD bodies) in Giemsa-stained smears of splenic aspirate (highest sensitivity, but carries a risk of haemorrhage given splenic fragility, requiring caution) or bone marrow aspirate (safer, standard alternative).
- rK39 rapid diagnostic test (immunochromatographic strip test) — detects antibody against a recombinant Leishmania antigen; rapid, field-deployable, now widely used as the first-line diagnostic tool in endemic-area programmes.
- Serology — direct agglutination test (DAT), ELISA.
- Culture — on NNN (Novy-MacNeal-Nicolle) medium, demonstrating promastigote growth; slower, used mainly in reference settings.
- PCR — highly sensitive, increasingly used where available.
- Supportive laboratory findings: pancytopenia, hypergammaglobulinaemia (with albumin-globulin ratio reversal), raised ESR.
Treatment: liposomal amphotericin B (increasingly the preferred first-line agent, particularly in the Indian subcontinent given resistance to older agents), miltefosine (the first effective oral antileishmanial drug), and pentavalent antimonial compounds (e.g., sodium stibogluconate — older standard, now limited by resistance in some endemic regions).
Complications: Post-Kala-azar Dermal Leishmaniasis (PKDL) — a cutaneous complication that can follow apparently successful treatment (particularly in the Indian subcontinent), presenting with hypopigmented macules/nodules, and importantly serving as a potential human reservoir maintaining transmission in the community, complicating elimination efforts.