MCQ of the Day: 27 October 2026

Answer: B. rK39 immunochromatographic test. Prolonged fever, massive splenomegaly, pancytopenia, weight loss and skin darkening in a resident of an endemic district of Bihar suggest visceral leishmaniasis (kala-azar) caused by Leishmania donovani. The rK39 rapid test detects antibodies to a recombinant kinesin antigen; it is cheap, needs only a finger-prick sample and has high sensitivity and specificity in the Indian subcontinent, so it is the field test used by India's kala-azar elimination programme alongside a compatible clinical picture. Because antibodies persist after cure, it cannot diagnose relapse.
A. The aldehyde test only shows raised polyclonal immunoglobulin; it is non-specific and has been replaced.
C. The leishmanin skin test reflects cell-mediated immunity, which is suppressed in active kala-azar, so it is negative during disease and turns positive after cure.
D. Splenic aspirate microscopy is the most sensitive parasitological method and culture can grow promastigotes, but it is invasive, carries a bleeding risk, needs a laboratory and takes days to weeks.