A patient from northeast India presents with fever, splenomegaly, anaemia, and hypergammaglobulinaemia. Peripheral smear shows large mononuclear cells. Direct agglutination test (DAT) is positive. Bone marrow aspiration reveals amastigotes within macrophages. What is the mechanism by which the causative organism evades macrophage killing?
- A Secretes IgA protease to destroy antibodies
- B Inhibits phagosome–lysosome fusion and acidification ✓
- C Produces catalase to neutralise hydrogen peroxide only
- D Resides exclusively in the cytosol avoiding the phagosome
Explanation
Leishmania donovani (visceral leishmaniasis) amastigotes survive within macrophage phagolysosomes by inhibiting phagosome–lysosome fusion and acidification, and by suppressing the oxidative burst through modulation of the PKC signalling pathway and inhibition of IFN-γ–mediated macrophage activation. They live within the phagolysosome (not the cytosol), which distinguishes them from Listeria/Shigella. Effective treatment requires miltefosine or liposomal amphotericin B, which activate macrophage killing. IgA protease is produced by Neisseria and Haemophilus, not Leishmania.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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